Digestion:

Your Digestive System And How It Works

The digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food.

Two solid organs, the liver and the pancreas, produce digestive juices that reach the intestine through small tubes. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system.

Why Digestion Is Important

When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nourishment. Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body. Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.

How Food Is Digested

Digestion involves the mixing of food, its movement through the digestive tract, and the chemical breakdown of the large molecules of food into smaller molecules. Digestion begins in the mouth, when we chew and swallow, and is completed in the small intestine. The chemical process varies somewhat for different kinds of food.

Movement Of Food Through The System

The large, hollow organs of the digestive system contain muscle that enables their walls to move. The movement of organ walls can propel food and liquid and also can mix the contents within each organ. Typical movement of the esophagus, stomach, and intestine is called peristalsis. The action of peristalsis looks like an ocean wave moving through the muscle. The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the food and fluid in front of them through each hollow organ.

The first major muscle movement occurs when food or liquid is swallowed. Although we are able to start swallowing by choice, once the swallow begins, it becomes involuntary and proceeds under the control of the nerves.

The esophagus is the organ into which the swallowed food is pushed. It connects the throat above with the stomach below. At the junction of the esophagus and stomach, there is a ringlike valve closing the passage between the two organs. However, as the food approaches the closed ring, the surrounding muscles relax and allow the food to pass.

The food then enters the stomach, which has three mechanical tasks to do. First, the stomach must store the swallowed food and liquid. This requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine.

Several factors affect emptying of the stomach, including the nature of the food (mainly its fat and protein content) and the degree of muscle action of the emptying stomach and the next organ to receive the contents (the small intestine). As the food is digested in the small intestine and dissolved into the juices from the pancreas, liver, and intestine, the contents of the intestine are mixed and pushed forward to allow further digestion.

Finally, all of the digested nutrients are absorbed through the intestinal walls. The waste products of this process include undigested parts of the food, known as fiber, and older cells that have been shed from the mucosa. These materials are propelled into the colon, where they remain, usually for a day or two, until the feces are expelled by a bowel movement.

Production Of Digestive Juices

The glands that act first are in the mouth the salivary glands. Saliva produced by these glands contains an enzyme that begins to digest the starch from food into smaller molecules.

The next set of digestive glands is in the stomach lining. They produce stomach acid and an enzyme that digests protein. One of the unsolved puzzles of the digestive system is why the acid juice of the stomach does not dissolve the tissue of the stomach itself. In most people, the stomach mucosa is able to resist the juice, although food and other tissues of the body cannot.

After the stomach empties the food and juice mixture into the small intestine, the juices of two other digestive organs mix with the food to continue the process of digestion. One of these organs is the pancreas. It produces a juice that contains a wide array of enzymes to break down the carbohydrate, fat, and protein in food. Other enzymes that are active in the process come from glands in the wall of the intestine or even a part of that wall.

The liver produces yet another digestive juice bile. The bile is stored between meals in the gallbladder. At mealtime, it is squeezed out of the gallbladder into the bile ducts to reach the intestine and mix with the fat in our food. The bile acids dissolve the fat into the watery contents of the intestine, much like detergents that dissolve grease from a frying pan. After the fat is dissolved, it is digested by enzymes from the pancreas and the lining of the intestine.

Absorption And Transport Of Nutrients

Digested molecules of food, as well as water and minerals from the diet, are absorbed from the cavity of the upper small intestine. Most absorbed materials cross the mucosa into the blood and are carried off in the bloodstream to other parts of the body for storage or further chemical change. As already noted, this part of the process varies with different types of nutrients.

Carbohydrates. It is recommended that about 55 to 60 percent of total daily calories be from carbohydrates. Some of our most common foods contain mostly carbohydrates. Examples are bread, potatoes, legumes, rice, spaghetti, fruits, and vegetables. Many of these foods contain both starch and fiber.

The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps: First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose; then an enzyme in the lining of the small intestine (maltase) splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body.

Table sugar is another carbohydrate that must be digested to be useful. An enzyme in the lining of the small intestine digests table sugar into glucose and fructose, each of which can be absorbed from the intestinal cavity into the blood. Milk contains yet another type of sugar, lactose, which is changed into absorbable molecules by an enzyme called lactase, also found in the intestinal lining.

Protein. Foods such as meat, eggs, and beans consist of giant molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. An enzyme in the juice of the stomach starts the digestion of swallowed protein. Further digestion of the protein is completed in the small intestine. Here, several enzymes from the pancreatic juice and the lining of the intestine carry out the breakdown of huge protein molecules into small molecules called amino acids. These small molecules can be absorbed from the hollow of the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.

Fats. Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is to dissolve it into the watery content of the intestinal cavity. The bile acids produced by the liver act as natural detergents to dissolve fat in water and allow the enzymes to break the large fat molecules into smaller molecules, some of which are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules to move into the cells of the mucosa. In these cells the small molecules are formed back into large molecules, most of which pass into vessels (called lymphatics) near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.

Vitamins. Another vital part of our food that is absorbed from the small intestine is the class of chemicals we call vitamins. The two different types of vitamins are classified by the fluid in which they can be dissolved: water-soluble vitamins (all the B vitamins and vitamin C) and fat-soluble vitamins (vitamins A, D, and K).

Water and salt. Most of the material absorbed from the cavity of the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid we swallow and the juices secreted by the many digestive glands.

How The Digestive Process Is Controlled

A fascinating feature of the digestive system is that it contains its own Hormone Regulators. The major hormones that control the functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine. These hormones are released into the blood of the digestive tract, travel back to the heart and through the arteries, and return to the digestive system, where they stimulate digestive juices and cause organ movement. The hormones that control digestion are gastrin, secretin, and cholecystokinin (CCK):

Additional Hormones In The Digestive System Regulate Appetite:

Both of these hormones work on the brain to help regulate the intake of food for energy.

Nerve Regulators

Two types of nerves help to control the action of the digestive system. Extrinsic (outside) nerves come to the digestive organs from the unconscious part of the brain or from the spinal cord. They release a chemical called acetylcholine and another called adrenaline. Acetylcholine causes the muscle of the digestive organs to squeeze with more force and increase the "push" of food and juice through the digestive tract. Acetylcholine also causes the stomach and pancreas to produce more digestive juice. Adrenaline relaxes the muscle of the stomach and intestine and decreases the flow of blood to these organs.

Even more important, though, are the intrinsic (inside) nerves, which make up a very dense network embedded in the walls of the esophagus, stomach, small intestine, and colon. The intrinsic nerves are triggered to act when the walls of the hollow organs are stretched by food. They release many different substances that speed up or delay the movement of food and the production of juices by the digestive organs.

Digestion Information: Natural News 6/30/2012 - Improve Your Digestion Naturally

Digestion Information: Dr. Kaslow - 5 Reasons To Eat Small Meals More Frequently

Digestion Information: Cancer Checklist - Digestion

Digestion Information: Dr. Ben Balzer,M.D. - Introduction To The Paleolithic Diet

Digestion Information: Dr. Mercola 1/6/2011 - Problems With Digestion?

Overview Of The Digestive System
Date: 9/28/2009
Posted By: Jon Barron
Edited To Fit This Format

Introduction And Getting Food Into The Digestive Tract

Effectively, this system is a continuous tube from the mouth to the anus -- something you probably don't want to think about the next time you kiss someone. Over the course of the next half dozen or so newsletters, I'm going to walk you through the digestive system -- from the tip of your tongue to the outer edge of your rectum. We're going to cover the anatomy and physiology of everything from your teeth to your bowel, plus the organs of digestion including the liver, gallbladder, and pancreas. All of this will help you understand the nature of diseases of the digestive tract (everything from hiatal hernia to acid reflux, from peptic ulcers to irritable bowel syndrome) and how to treat them naturally by working with your body, not against it.

Kissing

Along the way, I'm going to be challenging a number of medical assumptions. How can that be? Aren't anatomy and physiology pretty much cut and dried? And the answer is: "Not necessarily." As it turns out, the body responds differently according to what you eat, how you eat it, and how that food is prepared. Virtually, all physiological assumptions used by the medical community are based on observation of people eating the typical high speed modern diet. Change the diet, and you change the physiology.

And in fact, these differences are critical. It has been said that we dig our graves one forkful at a time. By understanding exactly how our body processes what we eat and how what we eat affects those processes, we can change our health outcomes. Effectively, we can delay the digging of our graves for years. And maybe even more importantly, we can enjoy those years with a much higher level of health and vitality. I'm sorry, but people who tell me they are perfectly healthy because they are successfully "managing" their acid reflux and Crohn's disease with medications are not actually healthy. They are merely suppressing the symptoms of unhealth temporarily.

Obviously, this is a huge topic and can't be covered in one newsletter. Effectively, I'm going to break the discussion into several pieces, including:

Digestive System Overview

Before we launch into the focus of today's newsletter, the mouth and esophagus, Let's take a quick overview of the entire system.

The digestive system is also known as the gastrointestinal (GI) tract and the alimentary canal and covers everything from the digestive tract itself to the organs that support it. It is a continuous tube like structure that develops outpouchings, which in turn evolve into those aforementioned attached digestive organs such as the pancreas, liver, and gallbladder. The entire system is about 40 feet in length from the mouth to the anus and is designed to transport food and water, modify it, and make it suitable for absorption and excretion. There are storage sites, excretion sites, and detoxifying sites along the way. And, according to the medical community, it has six primary functions.

  1. Ingesting food.
  2. Preparing food for digestion by physically grinding it and breaking it down into small pieces and unwinding proteins so they can be separated into their component amino acids.
  3. Actually breaking the food into molecular pieces that your body can use as nourishment.
  4. Transporting the food during its various stages of breakdown along the digestive tract in a measured, "manageable" flow.
  5. Absorbing the nutrients into the body. Absorption is the movement of broken down nutrients across the digestive tract wall and into the bloodstream for use by the cells of the body. Only water and alcohol are absorbed through the mucosa of the stomach and only in special circumstances such as severe dehydration. All the rest of absorption happens in the small intestine.
  6. Eliminating the unused waste products of digestion and absorption from the body.
    1. Digested waste products go to the kidneys
    2. Undigested waste products pass out through the colon and rectum.
    3. Ingested material that might otherwise be toxic is rendered harmless, primarily by the liver, and excreted from the body.

But that said, I now have my first disagreement with the medical community. I submit to you that the above list is incomplete, and that these omissions are not unimportant. For example, medicine has no understanding of the role your digestive system plays in maintaining an optimal environment for beneficial bacteria and why that's essential. Therefore, they both allow and, in fact, encourage by their treatments many diseases to manifest that should never appear -- and have no idea how to treat them when they do. And that's just one example that we'll explore in more detail later on. So, from a holistic point of view, the digestive system, in addition to the functions listed above, also performs the following functions:

Carnivore, Omnivore, Frugivore?

There is one other piece of overview information we need to cover. The medical community bases its assumptions concerning the human digestive system on the fact that it is essentially designed as an omnivore system. Only people at tailgate parties and gladiator games actually believe that we are pure carnivores. But, as I discussed in detail in "Lessons from the Miracle Doctors", this is simply not supported by the evidence at hand. And once again, this distinction is not subtle; and not insignificant. Yes, the human body has an amazing ability to adapt to any diet we throw at it -- but not without consequences. And, in fact, many of the diseases we face today are the direct result of not understanding what our systems are designed to handle and the consequences we face as a result.

How could the medical community be so wrong on this issue? Actually, it's very simple, and it's the same old problem. As usual, the medical community views the body as separate pieces, not as an integrated whole. It looks at things in isolation. In this particular case it looks at the diet of the 99% of population that passes through their doors in need of their care, and those people eat everything from cotton candy to slabs of grilled beef -- an omnivore diet. Given this context, for medical anatomists, the digestive system is undeniably designed for an omnivore diet. However, it takes only a slightly more holistic viewpoint to make a casual comparison of the structures of the human digestive system (teeth, stomach, and intestines) to other animals living in the wild to see how unsupportable that point of view is. And in fact, we will cover those differences in detail as we move through the digestive system and discuss each relevant organ.

And with all that said, let's now begin our trip through the digestive system.

Getting Food Into The Digestive Tract, The Mouth And Esophagus

Let's begin our exploration of the digestive system by examining the structures that play a key role in getting the food into the stomach. And since this is not an actual anatomy course, but a series of newsletters about how anatomy and physiology relate to alternative health, we will focus our discussion on the specific parts of the system relevant to our discussion and brush lightly over the rest.

Mouth

The mouth is the portal to the digestive system. Food enters the body through the mouth, where it is cut and ground by the teeth and moistened by saliva for ease in swallowing and to start the digestive process. The tongue assists in moving food around during chewing and swallowing and also contains the taste buds.

Teeth

Most medical texts suggest that our teeth are designed to eat all kinds of food from meat to fruit, thus proving that man is an omnivore. But as I mentioned earlier, the facts do not bear this out.

The first thing you notice about carnivores is that their teeth are nothing like those found in humans. They have huge canines for striking and seizing prey, pointed incisors for removing meat from bones, and molars and premolars with cusps for shredding muscle fiber. In carnivores, the teeth of the upper jaw slide past the outside of the lower jaw so that prey is caught in a vice-like grip. In general, carnivores don't chew much; mostly, they just tear chunks off and swallow them whole. All in all, nothing like human teeth.

But the claim in medical texts is that we are omnivores, not carnivores. How does that claim stand up? Well, first of all, no animal is really adapted to eat all things, but if any animal comes close, it would be the bear. Typical foods consumed by bears include ants, bees, seeds, roots, nuts, berries, insect larvae such as grubs, and even flowers. Some meat, of course, is eaten by bears, including rodents, fish, deer, pigs, and lambs. Grizzlies and Alaskan brown bears are well-known salmon eaters. Polar bears feed almost exclusively on seals, but then, what vegetation is there for them to eat in the frozen wastes of the Arctic? And, of course, anyone who has read Winnie the Pooh knows that many bears love honey. So, other than the ants, grubs, and rodents, the bear diet sounds a lot like the typical Western diet.

Among the great apes (the gorilla, the orangutan, the bonobo, and the chimpanzee) and ourselves, only humans and chimpanzees hunt and eat meat on a frequent basis. Gorillas have never been observed hunting or feeding on any animals other than invertebrates such as termites and ants. Nevertheless, chimpanzees are largely fruit eaters, and meat comprises only about 3 percent of their diet -- far less than is found in the typical Western diet.

Bottom line: at least as defined by our teeth, we do not qualify as carnivores or omnivores. So, at least as judged by our teeth, meat should comprise no more than 3% of our diet. But teeth do not comprise the end of the issues. Later on, we'll compare stomachs and intestinal tracts to see if we match up any better there.

Tongue

The tongue is the largest muscle in the mouth. It functions in chewing, swallowing, and forming words. The extrinsic muscles of the tongue (those muscles that originate outside the tongue itself) attach to the skull and neck, and they move from side to side and in and out. The intrinsic muscles attach to the tongue itself, and they alter the tongue's shape (for swallowing and speech). The most interesting parts of the tongue in terms of our discussion are the papillae, the bumps on the tongue that contain the taste buds.

Taste Buds

Taste buds are composed of groups of about 40 column shaped epithelial cells bundled together along their long axes. Taste cells within a bud are arranged such that their tips form a small taste pore. Minute, hair-like threads called microvilli extend through this pore from the actual taste cells. The microvilli of the taste cells bear the actual taste receptors, and it appears that most taste buds contain cells that bear receptors for two or three of the basic tastes.

There are four tastes we normally associate with taste buds: sweet, salty, sour, and bitter. However, research has identified a fifth taste our buds can identify. The fifth taste is umami, the taste of monosodium glutamate (no kidding), and has recently been recognized as a unique taste, as it cannot be elicited by any combination of the other four taste types. Glutamate is present in a variety of protein-rich foods, and particularly abundant in aged cheese.

Unless artificially disrupted, our sense of taste will guide us to the foods necessary for our survival. And, in fact, our taste preferences change according to our body's needs. Just ask the husband of any pregnant woman. Or more scientifically:

Now, there are three tastes I want to focus on.

Sweet

The sweet taste was designed to cause us to desire natural carbohydrates essential for our survival. As we discussed above, our teeth match those of the frugivores, largely fruit eaters. However, technology has allowed food manufacturers to exploit our desire for sweet things -- to our detriment. For the most part, concentrated sugars, other than honey, are not naturally available for us to consume. Table sugar is a manufactured creation, as is maple syrup, agave syrup, not to mention high fructose corn syrup, glucose, dextrose and all of the other concentrated sweeteners added to our food. If living in nature, our desire for sweets would lead us to low concentrations of sugar bound to fiber, not 32 oz Big Gulp sodas containing almost a cup of concentrated sugar. The bottom line is that these concentrated sweeteners feed an addiction because, based on evolution, our taste buds never expected to find concentrated sweeteners -- only natural foods, with a far less concentrated character. And to make matters even worse, the more concentrated sweeteners we eat, the more we crave.

Umami

A similar situation exists with umami, also known as "savory." In nature, this taste is never concentrated, and exists only in very small amounts in selected foods. Concentrating it as a food additive, confuses the system and allows us to consume glutamate in far higher levels than our bodies were ever designed to handle -- with highly disruptive health effects for sensitive people.

Bitter

And then there's bitter! Bitterness is the most sensitive of the five tastes. It has been suggested that the evolutionary purpose of "bitter" is to warn us against ingesting toxic substances, many of which have a bitter character. Unfortunately, this association between bitter and unhealthy is not entirely true, and our current culinary desire to avoid bitter tastes causes us to miss the health benefits associated with many bitters. Common bitter foods and beverages include coffee, unsweetened chocolate, bitter melon, beer, bitters, olives, citrus peel. But how many people eat them in their unadulterated form any more. Bitters are almost always masked by added sugar. In any case, whereas at one time people regularly consumed bitters as part of their diet, we pretty much completely avoid them now. When's the last time you saw a fast food or soda pop based on bitter?

This has major health consequences for your liver. The body has a number of built-in feedback loops, a number of which we'll cover as we move through the digestive system, such as the triggers that both stimulate and shut off the production of stomach acid. But the simple fact is that the taste of bitter in the mouth is stimulating to the liver. There is a direct feedback loop from the tongue to the liver. Every time you taste something bitter, your liver gets a positive jolt that stimulates it to put out more essential bio-chemicals and expel accumulated toxic waste. If you never taste any bitter, your liver tends to become sluggish over time and retain toxic build-up. This is one of the key reasons that the Liver Tincture and Blood Support formulas I use during detoxing have such a pronounced bitter taste. In fact, all of the great liver herbs, milk thistle, dandelion root, and Picrorhiza Kurrooa are decidedly bitter.

Nose/Smell

Although not usually considered, anatomically, as part of the digestive system, the nose really does qualify. After all, up to 75% of what we perceive as taste is due to smell. And the mere smell of certain foods can stimulate hunger and the production of digestive juices. Thus, simple nasal maintenance, such as daily nasal cleansing, is an important part of good intestinal health -- not to mention the fact that it washes out vast quantities of bacteria and viruses, thus preventing them from entering the digestive tract. Incidentally, the primary role of the uvula, the fleshy piece that hangs from the back of the throat, is to detect food that passes over it, and rise up during swallowing to close off the nose from the food so it can't back up into the nose.

Salivary Glands

There are three pairs of salivary glands that secrete saliva, the first of the digestive juices to contact the food in the mouth. They are:

Saliva performs several key functions. It moistens the mucous membrane, moistens food for easy swallowing, lubricates the esophagus for swallowing, washes the mouth, kills bacteria, dilutes poisonous substances, and contains enzymes that begin the digestion process. Your body produces from 1-1.5 liters of saliva per day (about a quart). More than 99% of that saliva is water, and almost all of it is reabsorbed in the digestive tract. The tiny bit of saliva that is not water contains about 0.05% enzymes:

Salivary Amylase Begins The Breakdown Of Carbohydrates

Your digestive system is remarkably adaptable; after all, it can handle pepperoni pizza, beer, and Ding Dongs. But there are consequences if you abuse it. There are two forms of abuse. First, there's eating a diet high in cooked and processed food that has destroyed all of the enzymes naturally present in the food. In this particular case, we're talking about amylase. All natural carbohydrates contain the amylase needed to digest them. In fact, the amylase found in wheat and other grains will actually work in the stomach at high acid pH levels of 3 to 4. If natural amylase is present, it will handle a great deal of the digestive process required to break down the carbohydrates you eat. Second, you need to chew your food thoroughly. If you chew your food well enough, it slows down the entire eating process, which spreads out the glycemic response. It also allows the amylase in the saliva to effectively start breaking down the carbohydrates, which takes a huge burden off your pancreas. And it allows time for your stomach to signal your brain that you're full (it normally takes twenty minutes for your brain to catch up with your stomach), so you end up eating less.

So, how much do you need to chew your food? There's an old saying: "You should drink your solids and chew your liquids." What that means is that you should chew the dry food you eat until it turns to liquid in your mouth (about forty chews per mouthful), and that you should swish liquids back and forth in your mouth (chew them as it were) an equal number of times. This helps mix enzymes into the food or liquid and begins the digestive process.

The more you chew, the more effective these enzymes are.

And if you don't do these things, how much does the body have to compensate? Amylase levels in the saliva of people eating the typical western cooked/processed diet are as much as 40 times higher than that found in people eating a more natural diet!

Note: During dehydration, the brain signals the mouth to stop the flow of saliva to impel us to drink more water and to conserve fluids.

Swallowing (Deglutition)

Once you start chewing your food and mixing it with saliva, it picks up a technical name; the wad of chewed food is called a bolus. During the voluntary stage of swallowing, the tongue moves the bolus of food upward and backward. Once the bolus reaches the back of the throat, all actions become involuntary -- they happen outside of your conscious control. During the first of these involuntary phases, the muscles move the food down and back into the esophagus. And finally, the food is actively moved through the esophagus to the stomach. By actively, I'm referring to the fact that movement through the esophagus is the result of series of active, coordinated movements by constrictor muscles lining the esophagus -- not the result of gravity. Specifically, longitudinal muscles pull the esophagus up and relax lower portions so that the circular bands of muscle lining the esophagus can constrict and move the bolus down into the stomach. In fact, although it is not advisable, you can easily swallow when hanging upside down.

As we discussed in our series on breathing, aspiration (entry of food or water) into the lungs and nasopharynx is prevented in a series of involuntary actions.

Esophagus ("Carries Food")

Although there are a number of things that can go wrong with the esophagus, they are mostly medical and fall outside the scope of our discussion. For our purposes, the only function of the esophagus is to carry food from the mouth to the stomach. No digestion or absorption of nutrients takes place in the esophagus. Liquids pass through quickly -- in about a second. A food bolus, on the other hand will take about five to nine seconds to make its way through the esophagus.

In fact, there is little to interest us from an alternative health point of view until we reach the lower esophageal sphincter, which is located at the end of the esophagus just above the diaphragm. The sphincter is not actually an anatomical structure. It's just an area at the end of the esophagus that is capable of constricting to effectively separate the stomach from the esophagus. When functioning properly, it allows food to enter the stomach while at the same time preventing stomach acids and bile from refluxing back into the esophagus.

From a medical point of view, there are a number of things that can go wrong with the lower esophageal sphincter, such as achalasia (inability to relax), which prevents food from entering the stomach. But for the purposes of our discussion, two conditions stand out: GERD and hiatal hernia. These conditions used to be handled surgically, but with rather poor results. Antacids provided temporary relief, but as we will learn when we discuss the stomach, actually aggravated the problems. Now, new drugs called proton pump inhibitors are the treatment of choice. They work by cutting the ability of the body to produce stomach acid and are more effective, from a medical point of view, than either surgery or antacids.

GERD

GERD (Gastro Esophageal Reflux Disease) is also known as acid reflux disease. It is a condition in which the sphincter fails to prevent acid from backing up into the esophagus. This causes inflammation, scarring, and can lead to esophageal cancer. We will talk more about GERD when we talk about acid production in the stomach, which is the primary contributing factor in this disease. We will also discuss why Prilosec, Prevacid, and Nexium may not be the best answers to this problem. One other note on acid reflux at this time is that hiatal hernia is often a contributing factor.

Hiatal Hernia

Hiatal hernia is a condition in which part of the stomach moves above the diaphragm, into the chest. They are much more common than generally recognized and can produce a wide variety of symptoms that make diagnosis difficult. Hiatal hernias can manifest as severe chest pains that mimic a heart attack, pressure in the chest, or severe stomach pain. And most notably, as mentioned above, a hital hernia can significantly aggravate acid reflux as it pushes the esophageal sphincter out of position, thereby seriously compromising its ability to prevent stomach acid from moving into the esophagus.

There are very few medical options for treating a hiatal hernia. As I mentioned earlier, surgical intervention is only marginally effective. The common medical approach today is to reduce the amount of acid the stomach produces with proton pump inhibitor drugs. But the use of these drugs is even more questionable for a hiatal hernia than for standard GERD as it does nothing at all to alleviate the underlying condition -- the fact that part of your stomach is now up in your chest cavity. It merely helps control one symptom.
Fortunately, there are alternatives.

Conclusion

That concludes our introduction to the digestive system -- getting food into the stomach. In our next issue, we will cover the stomach in detail. Areas of interest will include:

Date: 02/08/2010
Posted By: Jon Barron
Edited To Fit This Format

Anatomy Of The Small Intestine

We return to our exploration of the intestinal tract from a natural health perspective, but this time we shift gears a bit. So far, we've covered everything from the mouth through the duodenum (taking time to discuss the ancillary outpouchings along the way: the pancreas, liver, and gallbladder). And throughout, the emphasis has been on digestion. But now as we reach the small intestine, things change. Absorption becomes the dominant issue. Yes, a great deal of digestion still occurs in the small intestine, and we will cover that, but the overall emphasis is on absorption. In fact, if you ignore exceptions like the direct absorption of alcohol from an empty stomach, close to 100% of all nutrient absorption in the human body takes place in the small intestine. Obviously then, its proper functioning is crucial to our health.

In this issue, we will explore the anatomy of the small intestine to give us a functional understanding of how it is constructed to do its job and also provide us with a shared vocabulary that we can subsequently use as we explore exactly how the small intestine completes digestion of food and selectively absorbs the nutrients your body needs.

Macro Anatomy Of The Small Intestine

The small intestine, also called the small bowel, serves two primary functions in the body.

Technically, the small intestine begins at the pylorus valve that separates the stomach from the duodenum and ends at the ileocecal valve that separates the ileum from the large intestine. The bulk of the small intestine is suspended from the body wall by an extension of the peritoneum called the mesentery. The small intestine is approximately 20 to 23 feet long, depending on how and when it's measured, and it is divided into three sections:

Although precise boundaries between these three segments of bowel are not readily observed, there are microscopic structural differences among them.

Duodenum

The name duodenum actually derives from its length and literally means twelve inches. It runs from the pylorus valve to the ligament of Treitz (a band of smooth muscle that extends to the diaphragm and works to hold the small intestine in place). Although technically part of the small intestine, the duodenum is almost 100% involved in digestion, not absorption. As such, we have discussed it in great detail already and will not focus on it in this newsletter.

Jejunum

The jejunum runs from the ligament of Treitz to the mid small bowel and encompasses roughly 40% of the length of the small intestine. It has numerous muscular folds called plicae circulares, and we will explore it in some detail in the next newsletter. The term "jejunum" derives from the Latin and means "empty of food." The name, however, actually came from the ancient Greeks who noticed that at death this part of the intestine was always "empty of food." Hence, the name jejunum.

Ileum

The third division of the small intestine is the ileum, which runs from the mid small bowel to the ileocecal valve at the entrance to the large bowel (colon) and encompasses roughly 60% of the length of the small intestine. The word "ileum" comes from the ancient Greek and means "twisted," which actually has a dual meaning. First, when viewed during surgery (or after a Trojan sword has slit open your midsection), the ileum actually looks twisted. The second reference is that the ileum is most often the site of twists that can cause obstructions in the small intestine.

Pilcae Circulares

As mentioned above, when referencing the jejunum, the small intestine is not flat internally, but is thrown into circular folds. These folds are known as "plicae circulares" and are prominent inside the small intestine from the duodenum to the mid ileum. They serve a dual purpose:

Blood Supply Of The Small Intestine

Identifying the blood supply of the small intestine is more important for surgeons than for our discussion of the small intestine as it relates to natural health. Nevertheless, very quickly:

The Microstructure Of The Small Intestine

If examined closely, the surface of the small intestine has the appearance of soft velvet. This is because it's covered by millions of small projections called villi which extend about 1 mm into the lumen (the empty space inside the small intestine). But villi are only the most obvious feature of the intestinal wall. As we've already discussed, the mucosa (the innermost layer of the intestinal wall) contains a number of different cells including: a self-renewing population of epithelial cells, secretory cells, and endocrine cells. Let's look at the intestinal wall in a little more detail.

The small intestine has the same four layers as the rest of the GI tract, but they are modified for maximal absorptive power.

Villi

Villi are projections into the lumen covered predominantly with mature, absorptive enterocytes, along with a spattering of mucus secreting goblet cells. These cells live only for a few days, die and are shed into the lumen to become part of the chyme where they are digested and absorbed. And yes, if you wish to think of it that way, we are all cannibals eating our own intestinal walls. The word villi literally means "tuft of hair," which is exactly what the villi look like. In fact, they are fingerlike projections of the mucosa, with approximately 40 villi per sq mm inside the wall of the small intestine. As discussed earlier, each single villus contains an arterial and venus capillary (arteriole and venule) and a lacteal (the lymphatic equivalent of a capillary). Note" the lymphatic system is a circulatory system that exchanges fluid between cells, drains into veins in the neck, and can absorb fat. In the small intestine, the lacteals transport fat from the digestive tract into the circulatory system.

Microstructure Of A Single Villus

Each villus contains multiple absorptive cells on its surface. And protruding from the surface of these absorptive cells on each villus are a vast multitude of microvilli. Microvilli are minutely small hair like projections that serve to increase the surface area of each villus.

Microvilli lined up along the edge of a villus.

How many microvilli are we talking about?

Hold your breath. Each villus has approximately 200 million microvilli/sq mm. This creates a velvety surface on the walls of the small intestine known as the brush border.

And how much does the brush border of microvilli increase the surface area of the wall of the small intestine involved in nutrient absorption?

Again, hold your breath.

All in all, if the small intestine is viewed as a simple pipe, its surface area totals about half a square meter. But it is not a simple pipe. Factor in the mucosal folds, the villi, and the microvilli, and the absorptive surface area of the small intestine is in fact approximately 250 square meters - the size of a tennis court! This increases the absorptive power of the small intestine exponentially.

Intestinal glands are located in the crypts of Lieberkuhn at the base of the villus (see illustration above). The cells/glands here secrete intestinal juices. Toward the base of the crypts are stem cells, which continually divide and provide the source of all the epithelial cells in the crypts and on the villi. The way they divide is actually quite interesting. One daughter cell from each stem cell division is retained as a stem cell, thus perpetuating the untainted original source. The other daughter cell differentiates along one of four pathways to become either an enterocyte, an enteroendocrine cell, a goblet cell, or a Paneth cell. Enterocyte cells migrate up the crypts, and onto the villi, where they become the mature epithelial absorptive cells essential for extracting nutrients from the chyme. Virtually all nutrients, including all amino acids and sugars, enter the body across these absorptive cells that form the epithelium covering the villi.

Note: After crossing the epithelium of the villi, most nutritional molecules diffuse into the capillary network inside the villus diagrammed above, and then into the bloodstream. Some molecules, fats in particular, are transported not into capillaries, but rather into the lymphatic vessels (lacteals), which drain from the intestine and rapidly flow into blood via the thoracic duct.

Specifically, cells/glands found in the crypts of Lieberkuhn, at the base of villi, include:

Ileocecal Valve

The ileocecal valve is a small muscle located on the right side of the body (left side on most illustrations) between the small and large intestine, thus marking the end of the small intestine. It is essentially a one way check valve that allows the final stage of chyme to pass into the large intestine for final water extraction and stool making. (Note: once chyme enters the large intestine, it is called fecal matter.) If functioning properly, the valve will open and close as required. Unfortunately, it does not always function properly. Sometimes it sticks in the open position, which allows fecal matter to back up into the small intestine, where it can then contaminate the nutrient extraction process. And sometimes the valve sticks in the closed position, which can lead to constipation. Both of these conditions are very toxic and are easily triggered by bad diet (heavy alcohol consumption in particular), dehydration, and stress.

It should be noted that problems with the ileocecal valve are, for the most part, not acknowledged by the medical community, almost never diagnosed, and no effective treatments are offered. Fortunately, there are highly effective natural health options.

Conclusion

In our next issue of the newsletter, we will begin an exploration of exactly how the small intestine (based on its anatomy) does its job -- both mechanically and chemically. We will also discuss its physiology, what can go wrong, and how we can fix it without the need for surgery or debilitating pharmaceutical drugs.

Date: 03/08/2010
Posted By: Jon Barron
Edited To Fit This Format

Physiology Of The Small Intestine, Part 1

And now we reach the heart of the intestinal tract. Everything so far has been preparation for this discussion. Digestion, or breaking food down into smaller bits, is certainly important -- crucial even -- but to what purpose? The purpose, quite simply, is to get the nutrition inherent in the food you ate ready so that it can be absorbed into your body where it can be used by each and every single cell to survive and carry on its individual function. When it comes to the intestinal tract, the key is absorption. It's not what you eat or digest that matters; It's what you absorb. And when it comes to absorption, the small intestine is the portal for virtually all nutrients that enter into the bloodstream.

Note: much of this discussion is easy to understand, but the core of it, the actual act of absorption is quite technical and involves some chemistry. As always, I will only deal with as much chemistry as is absolutely necessary -- and will present it in such a way as to make it comprehensible.

Digestion -- Setting Up Absorption

Before we can get to absorption, we have to cover the final stages of digestion that take place in the small intestine. In fact, you get a combination of mechanical and chemical digestion and some absorption in the small intestine. Early in the intestine it is mostly digestion, very little absorption. However, the further on you move down the digestive tract, the more the ratio swings in favor of absorption. Effectively, the entire small bowel (duodenum, jejunum, and ileum) is devoted to these two processes: digestion and absorption. Digestion itself is divided into mechanical and chemical phases.

Mechanical Digestion

Mechanical digestion, as we alluded to in our exploration of the anatomy of the small intestine, is the result of two very different, but complementary actions:

Segmentation represents localized activity in the small intestine, whereas peristalsis represents the more global movement that takes place throughout the entire intestinal tract.

In segmentation, circular muscles constrict and divide the small bowel into segments -- each about 3-4 inches long. A muscle then contracts between the two other muscles and subdivides the segment. This is repeated many times per minute so that the chyme is moved back and forth in the same area of the segment. Localized contractions crush and mix food within that segment alone. This action mixes the chyme with intestinal juices and prolongs its contact with the absorptive surface of the small intestine. Relaxation allows the segments to coalesce, thus allowing chyme to move on down the intestinal tract -- pushed by peristalsis.

Peristaltic contractions represent a global movement that is designed to move chyme through the entire length of the small intestine and ultimately complement the mechanical process of segmentation that holds chyme in individual segments of the intestinal tract. Peristalsis is completely under the control of the autonomic nervous system and is coordinated by the myenteric plexi (plexuses). The myenteric plexus, also known as Auerbach"s plexus, is a network of nerves between the circular and longitudinal layers of the muscles surrounding the intestinal tract.


Segmentation in a sheep's small intestine

It should be noted that peristaltic activity is weak (as opposed to segmentation), which means that food stays in the small bowel for a relatively long time (4-6 hours). And it should also be noted that peristalsis can be fairly easily slowed or even stopped by outside factors. Culprits include appendicitis, surgery, medication, and even very large meals. On the other hand, there are certain things that can increase peristalsis such as laxatives and certain kinds of illness or toxicity. As anyone who has experienced food poisoning or stomach flu would know, peristalsis is quite capable of shooting food through the intestinal tract when required. In simple terms, the body responds to toxins in the intestinal tract by adhering to the old bromide, "The solution to pollution is dilution." In effect, the body pours fluid into the intestines and increases peristalsis to eject and weaken toxins in cases such as bacterial contamination. In extreme situations such as presented by cholera, victims may actually die of dehydration from massive diarrhea. Note: in cases of massive diarrhea, you cannot drink enough water to compensate for the loss of fluids. Without the use of massive IV's, you will die of dehydration.

It should also be noted that in the period between meals, when the small intestine is for the most part empty, peristaltic contractions continue throughout the entire small intestine. Think of it as housekeeping activity, designed to sweep the small bowel clear of debris. This movement is the cause of "growling" that can be heard when people have not eaten for awhile.

Chemical Digestion

By the time chyme reaches the small bowel, it is a mix of partially digested carbohydrates, lipids, and proteins -- not yet ready for absorption. Digestion must be completed in the small intestine, because the colon will not absorb nutrients to any significant degree. As I mentioned earlier, the ratio of digestion to absorption changes dramatically as the chyme moves through the small intestine and is exposed to ever more chemical digestion. Specifically, digestion for each type of nutrient proceeds as follows.

Proteins

Proteins are denatured (unwound) by acid and broken down by pepsin in the stomach. For the most part, they arrive as polypeptides (short-chain amino acids) in the small intestine. The extent of breakdown into polypeptides is dependent on several factors such as:

Any breakdown not accomplished in the stomach must now be compensated for in the small intestine -- in addition to the small intestine's role in breaking down short-chain amino acids into even smaller molecules capable of being absorbed into the bloodstream. In either case, after proteins leave the stomach, breakdown continues in the small bowel by activated pancreatic enzymes, including trypsin, chymotrypsin, and elastase (which breaks down elastin fibers). All three are necessary because they each act at different places in the amino acid sequences.

In addition, brush border cells of the small bowel excrete more peptidases -- enzymes such as aminopeptidase and dipeptidase -- that complete the splitting of the amino acids into ever smaller components. Ultimately, this creates molecules small enough to transport across the brush border cells and into the bloodstream.

Lipids (fats)

Some lingual and gastric lipases (fat digesting enzymes) have already been at work, but the major job of fat digestion takes place in the small bowel. Again, if fats are consumed uncooked or unprocessed or if supplemental digestive enzymes are consumed with the meal, the equation changes. But in lieu of that, at this point in the process, fats are composed mainly of triglycerides (three fatty acids bound to glycerine). It is the action of pancreatic lipase in the small bowel that breaks them down into smaller, potentially absorbable components. Specifically, pancreatic lipase splits off a monoglyceride, leaving two of the lipids still attached to the glycerine.

To a significant degree, the ability of pancreatic lipase to break down lipids is regulated by how soluble those fats have become. It should be noted that lipids in their natural state are not water-soluble (that is, they do not dissolve in water). This is where bile, regulated by the gallbladder, comes into play. Bile salts (from the liver and gallbladder) emulsify (break into small droplets) the fat for easier entry into water solutions or more technically, into water suspensions. If you have gallstones, or have had your gallbladder removed, you will tend to have incomplete breakdown of lipids in your small intestine, resulting in fatty stools and a tendency to intestinal discomfort. In addition, and even more important, malabsorption of lipids prevents the body from receiving any of the nutrients dissolved in the fat. We are talking about vitamins A, E, and D, tocotrienols, and Omega 3 fatty acids to name some of the more familiar ones.

Carbohydrates

Unless you chewed your food properly (to pick up amylase from your saliva), or took supplemental enzymes with your meal, carbohydrates, for the most part, enter the small intestine intact. Once there, however, they are cleaved into sugars by pancreatic amylase. Further down the small bowel, maltase, sucrase, lactase, isomaltase and alpha dextrinas, secreted by the brush border cells, act on the remaining carbohydrates, cleaving off the component simple sugars one sugar at a time. For example:

Note: pancreatic lipase and amylase in the blood are used to measure abnormal function of damaged pancreatic cells.

Absorption

Again, everything we've talked about so far is about preparing the chyme for absorption into the bloodstream. Ninety to ninety-five percent of nutrition is absorbed in the small bowel. By the time chyme has reached the small intestine, it has been mechanically broken down and reduced to a liquid by chewing and by mechanical grinding in the stomach. In addition, partial chemical digestion may already have taken place as the result of enzymes in the food itself and enzymes found in saliva. As discussed previously, the effect of those enzymes can be extensive (up to 70% of total digestion) or virtually non-existent depending on how cooked and processed the food is and how much it is chewed. The use of supplemental digestive enzymes, of course, can change that equation dramatically. And finally, the action of stomach acids and pepsin serve to denature proteins and begin the process of breaking them down, making them readily amenable to final breakdown in the small intestine.

Thus, once inside the small intestine, the "partially" digested chyme is exposed to pancreatic enzymes and bile, which ultimately break down the chyme into "component" forms of protein, carbohydrates, and fats capable of being absorbed.

By the end of its passage through the small intestine, virtually everything of value to the body has been extracted from the chyme. We're talking about:

Let's now look at this process in detail.

The Absorption Of Water In The Intestinal Tract

Virtually all of the water that enters your intestinal tract, in whatever form, is absorbed into the body across the walls of the small intestine -- primarily through the action of osmosis. Incidentally, osmosis is defined as the movement of water across a semi-permeable membrane from an area of high water potential (closer to distilled water) to an area of low water potential (water that contains a lot of dissolved osmotically active molecules such as electrolytes and some nutrients). Incidentally, since its molecules are so large, the chyme that enters the intestinal tract from the stomach has only a minimal impact on osmotic pressure. However, as it is progressively broken down, its ability to increase osmotic pressure rises dramatically. For example, undigested starch has little effect on osmotic pressure, but as it is digested, each starch molecule breaks down into thousands of molecules of maltose, each of which is as osmotically active as the single original starch molecule. The net effect is to increase the osmotic pressure by a factor of several thousand times over the original starch molecule. Thus, as digestion proceeds, the osmotic pressure increases dramatically, thereby pulling water into the small intestine. In addition, crypt cells at the base of each villus (in the duodenum and jejunum) secrete electrolytes (chloride, sodium, and potassium) into the small intestine which further increases the osmotic pressure to pull water into the lumen (the empty space in the small intestine). On the other hand, as the osmotically active molecules (maltose, glucose, amino acids, and electrolytes) are absorbed out of the lumen and into the bloodstream, osmotic pressure decreases relative to the electrolyte rich water of the bloodstream, and water is thus reabsorbed back into the body.

The bottom line is that if the secretion and absorption of water doesn't balance, we become either bloated or dehydrated. With that in mind, we can take a look at a water balance sheet.

PRODUCTIONINTAKE
Saliva1.0 Liter
Swallowed Liquids2.3 Liters (most contained in the food we eat)
Gastric Juice2.0 Liters
Bile1.0 Liter
Pancreatic Juice2.0 liters
Intestinal Juice1.0 Liter (primarily from brush border cells)
Total9.3 Liters (average 154 lb man)
RECYCLEDEXCRETED
Small Intestine Reabsorption8.3 liters
Colon Reabsorption1.0 liter
Excreted In Feces0.1 liter
Total9.3 Liters (average 154 lb man)

Thus we can see that the water that enters the digestive tract and that is used in the digestive process is matched to a remarkable degree by the water that is recycled and excreted. In a healthy body, they are perfectly balanced, give or take a tenth of a liter. Keep in mind that the water lost through other means needs to be accounted for in balancing intake and outflow for the entire body. Sweat, for example, can account for anywhere from 100 to 8,000 ml (about 8.5 quarts) lost per day. You lose another quart as water vapor that passes out of your body as you breathe each day -- as anyone knows who watches their breath on a cold day. The amount lost in your urine will pretty much balance out the difference between the amount above and beyond the bare 2.3 liters you consume in your drink and food and the tenth of a liter lost in your feces and what you lose in your perspiration and breath. The bottom line is that your body will seek to balance the intake and outflow of the water it deals with every day -- to prevent bloating or dehydration. At any point it fails to do so, you will end up visiting your doctor.

Keep in mind that even small imbalances between fluid intake and output can cause major problems. Diarrhea is a common symptom of disease and can kill patients through dehydration. On the other hand, rapid over-consumption of water or other liquids, though rare, can cause a rapid drop in sodium and electrolyte levels in the bloodstream and can cause death. Or if your body loses the ability to effectively pass water through your kidneys, you suffer from edema (swelling in your legs), which puts an added burden on your heart.

So, how much water should you drink in addition to what you get in your food? Despite some medical claims to the contrary, I'm still a big fan of 64 ounces a day -- give or take, as circumstances dictate (body weight, temperature, how much you perspire, etc.).

Date: 03/08/2010
Posted By: Jon Barron
Edited To Fit This Format

Physiology Of The Small Intestine, Part 2

In our last issue, we explored the physiology of digestion in the small intestine and started our discussion of nutrient absorption. In this issue, we conclude that discussion. Effectively, this is the heart and soul of our entire series on the digestive tract. Ultimately, everything that happens in the digestive tract is designed to get nutrients into the bloodstream. The final step in the process, absorption, is in many ways the most fascinating part of the discussion. Stomach acid unwinding proteins and pepsin breaking them down, that is simple stuff. How the body actually recognizes amino acids and peptides and then transports them across the wall of the small intestine, that"s remarkably complex and fascinating and important to understand in terms of optimizing your nutritional uptake and, ultimately, your health.

Note: this is a fairly technical discussion. However, my goal is to make sure you understand enough of it so that:

Absorption

As we discussed in our newsletter on the anatomy of the small intestine, virtually all nutrients, including all amino acids and sugars, enter the body by crossing the enterocytes (the absorptive cells found in the small intestine), that make up the epithelium layer that covers each and every villi (the hair like extensions that project from the wall of the small intestine). There are two routes by which molecules make their way from the small intestine into the bloodstream:

For the most part, the tight junctions of the paracellular route are impermeable to large organic molecules such as dietary amino acids and glucose. Those types of molecules are transported exclusively by the transcellular route. Transcellular absorption of nutrients can take place by active transport or by diffusion. Active transport involves the expenditure of body energy, whereas diffusion occurs simply through random molecular movement and, therefore, without the use of body energy. Water for example, is transported through the intestinal mucosa by diffusion (isosmotic absorption); on the other hand, the absorption of amino acids and sugars involves active transport. This is one of the main reasons that eating a large meal can put you to sleep. You literally exhaust your body digesting and absorbing nutrients -- until down the road, those same nutrients ultimately make their way into your body's individual cells, thus, once again energizing you. Depending on the food you eat, you gain on the exchange -- deriving more energy as the cells absorb the nutrients than was lost in digesting those nutrients and getting them into the bloodstream.

In any case, after passing through the epithelium into the villi, most of these molecules then cross over into the capillary network found inside each villus, thus making their way into the bloodstream. Fats, as we discussed when exploring the anatomy of the small intestine, behave differently. Instead of diffusing into the capillaries, they make their way into the lacteals, the lymphatic vessels present in each villus. From there, they drain from the intestine and rapidly flow through the lymphatic system and ultimately into the bloodstream by way of the thoracic duct.

The process of crossing the epithelium into the villus, however, is not simple. In fact, the process varies for each nutrient. Or to put it another way, the epithelial tissue covering the villi is not uniform throughout the small intestine -- or for that matter, from top to bottom in a single villus. Individual epithelial cells vary in both their makeup and functionality. In fact, each villus has a multitude of different receptor sites, specific for each nutrient. Each type of protein fragment and each type of carbohydrate fraction has its own particular receptor site it uses for absorption. In addition, as mentioned earlier, some nutrients diffuse through the spaces between the epithelial cells (the paracellular route) -- spaces that vary throughout the intestinal tract, which has a significant impact on permeability. This becomes particularly important when we talk about the absorption of supplemental proteolytic enzymes (which are protein molecules). Unlike food proteins, proteolytic enzymes can actually use the larger spaces between cells to transport themselves out of the small intestine.

The bottom line is that as chyme (the mixture of broken down food and digestive juices) travels through the small intestine, it is exposed to a wide variety of absorption sites, each with very different characteristics. These absorption/receptor sites differ in the number and type of transporter molecules found in the plasma membranes of each individual cell. And once again, keep in mind, each individual villus is comprised of multiple enterocytes,each with a multitude of receptor sites. In other words, there are a vast number of receptor sites in the small intestine.

The Chemistry Of Absorption

The key to the absorption of most nutrients in the small intestine is the electrochemical pump powered by electrolytes (primarily sodium) which works across the epithelial cell boundary of the villi. In fact, this is not unique to cells in the small intestine. Every single cell in the body is required to maintain a low concentration of sodium inside the cell (with a correspondingly high concentration of sodium outside the cell), which is required for the movement of nutrients into the cell and waste out of the cell. Correspondingly, potassium levels tend to be high inside cells and low in the areas just outside them. In addition, the sodium pump requires the presence of a large number of Na+/K+ ATPases (ATP enzymes) to regulate and power the reaction. This means that the cells of the body require the expenditure of energy (in the form of ATP) to power the sodium pump. The purpose of the sodium pump is to pull nutrients into the cell as sodium flows in and move waste out of the cell as potassium moves out. With that said, It's now time to bite the bullet and get specific as to how nutrients move in and out of cells.

Every cell in the small intestine has three types of gateways that combine to move nutrients in and waste out.

By the way, there are approximately 150,000 sodium pumps per small intestinal enterocyte (cell). Each single cell is thus able to transport about 4.5 billion sodium ions into each cell per minute -- along with accompanying nutrients. So with that in mind, Let's explore these specialized means of absorption in some detail:

Carbohydrates

Most dietary carbohydrates (even most simple sugars such as sucrose and lactose) cannot be absorbed in the intestinal tract. The monosaccharides (glucose and galactose), on the other hand, are actively transported with sodium. Monosaccharides, however, are only rarely found in normal diets. Rather, as described in Part 1 of our discussion of the Physiology of the Small Intestine, they are derived by enzymatic digestion of more complex carbohydrates in the small intestine. In summary, glucose and galactose are taken into receptor sites found on the villi by co-transport with sodium using the same transporter.

Now, for the briefest of moments, let's get technical. (Hang in there; it's actually understandable.)

The specific transporter molecule that carries glucose and galactose into the absorbing cell on the intestinal wall is SGLUT-1, also known as the sodium-dependent hexose transporter. This molecule will only transport the combination of a glucose and sodium ion into the cell together; it will not transport either molecule alone.
It works as follows:

Once inside the enterocyte, glucose, galactose and fructose are transported out of the cell through another hexose transporter called GLUT-2 and on into capillaries that are found within each villus.

As we've already discussed, this is called active transport because it requires the use of ATP and requires the expenditure of some energy both for pulling the sugar molecules into the enterocyte, and then on out of the cell into the bloodstream. However, some time later, after using the sugars to power the body's cells, the end result is a net gain of energy.

Fructose, of course, is the other simple sugar readily absorbed in the small intestine. The transport of fructose, though, involves an entirely different process. It is absorbed through something called facilitated diffusion (facilitated by Glut5) and requires no added energy (ATP) to cross into the bloodstream. The ability of fructose to be absorbed so easily into the system is indicative of its high reactivity in the body -- and therefore also indicative of some of the problems it can present when consumed in a "pure" form such as high fructose corn syrup. When bound with fruit fiber, it behaves differently. It breaks down more slowly and is absorbed more slowly -- thus presenting fewer problems.

As we mentioned earlier, the receptor sites for sugars are specific for sugars. This allows for an interesting option. Certain forms of fiber (which are also carbohydrates) can actually fill these receptor sites making them unavailable for use by the sugars for about an hour. Now, although these fibers can fill the sites, they are not transported into the cell. Instead, they occupy the site for up to an hour (again making those sites unavailable to any sugars for that period of time) until they are eventually rejected by the gateway and move out of the receptor site, then on down the digestive tract and out through the large bowel. Why is this important? Because the use of a sugar metabolic enhancement formula based on these fibers can modulate sugar uptake -- slowing down and evening out the absorption of sugar -- thus helping to avoid insulin spikes. The health benefits can be profound.

Proteins

After digestion, the proteins consumed in our food have been broken down into single amino acids, dipeptides, and tripeptides. These protein "pieces" are actively transported across the duodenum and jejunum. In fact, the mechanism by which amino acids are absorbed is virtually identical to that of monosaccharides, but takes place in different receptor sites. Amino acids are transported by sodium through nutrient gateways built into the cell walls of enterocytes. Dipeptides and tripeptides, on the other hand, are transported in a similar manner, but with hydrogen, not sodium, as the transporter. Again, since we're talking about active transport involving the use of ATP, varying amounts of energy are required in the absorption of proteins.

It should be noted that as with carbohydrates, the transporter receptor sites are specific to amino acids and specific to different types of amino acids. In fact, there are several sodium-dependent amino acid transporters -- including one each for acidic, basic, and neutral amino acids. Once again, these transporters bind their specific amino acids only after binding sodium. The fully loaded transporter then dumps sodium and the amino acid into the cell's cytoplasm, followed by its reorientation back to its outward facing position.

Lipids

After digestion, the fats in our meal have been broken down into fatty acids, monoglycerides, and glycerol. They are absorbed primarily by simple diffusion of small particles across the brush border (the name for the microvilli-covered surface of the epithelial cells that line the small intestine) and by a small amount of active transport. The key here is the size of the fatty particles; they must be small in order to be absorbed. That's where bile salts come in. The presence of a controlled flow of bile salts which break up the fats into tiny particles is essential for proper absorption of fats. If your gallbladder is not functioning properly or has been removed, you will have a problem absorbing fats. If you have a problem digesting fats for any reason, an option is to use ox bile tablets available at most health food stores. Supplemental digestive enzymes with lipase will also assist.

Another lipid of importance that is absorbed in the small intestine is cholesterol. As it turns out, cholesterol is readily absorbed in the small intestine. Specifically, a transport protein (NPC1L1) has been identified that transports cholesterol from the lumen (the interior space) of the small intestine into the enterocytes.

Note: unlike proteins and sugars, fats do not go directly into the bloodstream. They transport into the lacteals (tiny lymphatic ducts) found in the villi, and then travel through the lymphatic system and ultimately into the bloodstream. And in fact, fats do not enter the bloodstream in the form in which they were absorbed into the enterocyte. Once inside the enterocyte, fatty acids and monoglycerides are synthesized into triglycerides. These triglycerides are then packaged with cholesterol, lipoproteins, and other lipids into particles called chylomicrons. It is the chylomicrons that actually are transported into the lacteals and on into the bloodstream. Many doctors believe that a high triglyceride count in your bloodstream is actually more indicative of potential heart problems than a high cholesterol number.

Omentum

Okay, we need to revert to a little anatomy for a moment and talk about the omentum. It's not really an organ, and it doesn't really relate to digestion or absorption so it hasn't made any sense to talk about it so far in our series on the intestinal tract. It does, however, relate to fat storage, and in that regard it makes sense to talk about it in terms of what happens to a large chunk of the fat we absorb.

The omentum actually has two parts -- the greater and the lesser. To keep things simple we'll focus on the greater omentum, which hangs from the bottom of the stomach and extends down the abdominal cavity, then back up to the posterior abdominal wall after connecting with the transverse colon. The greater omentum is mostly made up of fat. It stores fat and provides a rich blood supply to the stomach. Specifically, it plays the following roles:

For the most part, these are "medical" considerations, but one aspect of the omentum will ring a bell for many readers. Sometimes when people lose a lot of weight, they wonder why their stomachs are still large and fatty. It's often because of the fat stored in the omentum. The fat in the omentum is often the last fat to go when losing weight. If you want to lose the gut, you have to lose the fat from the omentum too.

Note: the lesser omentum is an attachment of the peritoneum that lies between the liver and the upper edge of the stomach. It carries the vessels that run to the stomach and liver.

Vitamins And Minerals

The thing to understand about vitamins and minerals is that for the most part, your body doesn't like isolates, can't absorb them, and considers them toxic if by chance they are absorbed. In general, your body prefers its vitamins and minerals bound to food -- in their natural form, primarily bound to carbohydrates and some proteins. In fact, as might be guessed from all that we've learned about absorption in the small intestine, It's actually the small lipids, sugars, and amino acids attached to the vitamins and minerals that the individual cells of your body recognize and absorb, not so much the vitamins and minerals themselves. Effectively, they just tag along for the ride into the cells. All that said, there are still important differences in how the different vitamins and minerals are absorbed.

Fat Soluble Vitamins

Assuming that your liver and gallbladder are working properly and that bile salts are breaking fats down into smaller, more absorbable particles, there is little problem absorbing the fat soluble vitamins -- even when in an isolated form -- such as d-alpha-tocopherol vitamin E. The bottom line is that the fat soluble vitamins (including vitamins A, beta- carotene, D, E and K) are diffused right along with their lipid carriers across the brush border of the cells found in the ileum. Likewise, they then travel with their associated fats on into the lymph system and then into the bloodstream.

The problem with using vitamin isolates when supplementing the fat soluble vitamins is not one of absorption or even one of toxicity (where the body thinks the isolate is a toxin). Rather, the problem is one of completeness. For example, consuming vitamin E as d-alpha-tocopherol leaves behind the seven other components of vitamin E (gamma, beta, and delta tocopherol -- plus the four tocotrienols: alpha, beta, gamma, and delta). Likewise, supplementing with beta carotene or vitamin A leaves behind the several hundred other carotenoids that usually accompany them in nature -- such as alpha carotene. Is that important?
Yes, very!

Studies have shown that alpha carotene is one of the most powerful carotenoids and has a strong inhibitory effect on the proliferation of various types of cancer cells such as those affecting the lungs, stomach, cervix, breast, bladder and mouth. It works by allowing normal cells to send growth-regulating signals to premalignant cells. Carrots, for that matter, contain approximately 400 different carotenoids in addition to beta carotene, and many of those carotenoids are far more powerful than beta carotene itself. If all you're getting is beta carotene, you're missing out. And if all you're getting is synthetic beta carotene, you may actually be hurting yourself.

Water Soluble Vitamins

The water soluble vitamins such as vitamin C and most of the B vitamins are mainly absorbed in the jejunum. They are taken into receptor sites found on the villi by co-transport with sodium using the same transporter system used to carry monosaccharides into the bloodstream. These vitamins do present a problem when allowed to enter the bloodstream as isolates, no longer bound to their appropriate carbohydrates. First, by not being bound to the carbohydrates, it severely limits the amount of absorption that can take place (much of the supplement is wasted and passed on out through the rectum). Second, if absorbed in an isolated form, they are toxic to the body and are carried to the liver as "poisons." The liver then neutralizes their toxicity through a process called conjugation that combines them with proteins. Although conjugation of water soluble vitamins stresses the liver (forcing it to do extra work), it does neutralize the toxic effect of the isolated water soluble vitamins and makes them usable by the cells of your body.

Minerals

Minerals are absorbed in a small area at the top of the duodenum next to the pyloric valve where chyme passes out of the stomach. This is the primary absorption site for the bivalent minerals, including iron, calcium, magnesium, and zinc. The problem with minerals is that they are not easily absorbed in their raw isolated state (think oyster shells and iron filings) because of their electrical charge, which is opposite that of the intestinal wall. At first glance, this might seem like a good thing since opposite charges attract. Unfortunately, they attract to the extent that the minerals "stick" to the intestinal wall and do not get absorbed into the bloodstream. Eventually, the chyme moving through the intestinal tract pushes these "sticky" minerals down through the small intestine and on out through the rectum. Absorption of isolated minerals is about 3-5%. In a non isolated state, when bound to food, the charge is hidden, and absorption will be some ten times greater.

Manufacturers selling vitamin isolates, use a compromise. They chelate their minerals by wrapping amino acids around them. The amino acids "cover" the electrical charge and allow the minerals to be absorbed in the duodenum. Unfortunately, although the charge is obscured, isolates are not user friendly when it actually comes to utilization by the individual cells. In this case, absorption and utilization by individual cells are not the same thing and the rate of cell utilization is significantly less with chelated minerals. Food bound minerals, on the other hand, are easily absorbed through the small intestine AND they are readily utilized by every cell in the body.

An exception to this rule is what some marketers call "ionic minerals." This is just a fancy way of saying that the mineral particles in the supplement (usually in a liquid form) are so small that the electric charge they generate is not strong enough to prevent its absorption. The bottom line is that good ionic mineral supplements (or their equivalent) are readily absorbed.

One other factor to consider is that the bivalent minerals are competitively absorbed because the area of absorption in the duodenum is relatively small. This means that an excessively high intake of one bivalent mineral in particular may occupy the entire absorption area and make the absorption of other bivalent minerals difficult. It also means that you need to supplement your minerals in an evenly balanced form rather than mega dosing on one mineral. To look at it another way, taking regular high doses of iron will impede the absorption of calcium, magnesium, and zinc leading to a series of other nutrition problems.

Proteolytic Enzymes

Many so called experts say that you cannot absorb proteolytic enzymes. First, they claim that as proteins, they are broken down by stomach acid and pepsin in the stomach unless they are enterically coated. Then other experts say that even if they did survive, their molecules are too big to pass through the walls of the small intestine. Whenever, I hear these arguments, I'm always reminded of the apocryphal story of the engineer who proved that bumblebees can't fly. Applying the principles of aerodynamics, he PROVED that based on their size, weight, the size of their wings, and the physiological limits of how fast they could flap them, that bumblebees could not fly. Of course, how valid is a proof when the evidence before your eyes demonstrates It's nonsense?

The absorption of proteolytic enzymes is a lot like the story of bumblebees. In the end, it doesn't matter how many ways you try and prove that they can't be absorbed; in the end, you can both measure them in the bloodstream and, more importantly, quantify the results of their presence in your own body.

In any case, Let's first deal with the digestive juice issue first. There are two rebuttals:

When I designed my own proteolytic formula, pHi-Zymes, I specifically selected enzymes that survive the stomach environment. It's actually not that hard to do. The key is to use non-animal derived enzymes. Oral supplementation with non-animal derived enzymes, such as microbial enzymes, those manufactured by a fermentation process of Aspergillus, for example, possess unusually high stability and activity throughout a wide range of pH conditions (from a pH of 2-10). This enables them to be more consistently active and functional for a longer distance as they are transported through the digestive tract. Bottom line: they are not destroyed by stomach acid or pepsin.

Now Let's address the issue of absorption. The standard medical assumption is that no dietary protein is absorbed in an undigested form -- pretty much without exception. Rather, since their molecules are too large, dietary proteins first must be digested into amino acids or di and tripeptides before they can be absorbed. At first blush, that seems to exclude undigested enzymes (which are indeed proteins) from absorption. The clinker, though, is that enzymes, although they are proteins, are not dietary proteins. They are very different in function and structure; they are biochemical catalysts. In fact, enzyme molecules are much smaller than dietary proteins. In fact, they are smaller than DNA molecules. They are indeed small enough to be absorbed. The bottom line is that supplemental proteolytic enzymes can cross the intestinal wall.

How exactly then are they transported across the mucosal membrane of the small intestine? The definitive answer appears to be unknown at this time. Nevertheless, studies indicate that proteolytic enzymes are able to increase the permeability of the mucosal epithelium and, hence, facilitate their own absorption by a mechanism of self-enhanced paracellular diffusion (i.e., across the tight junctions between the epithelial cells).

At this point, it is probably worth abandoning our attempt to argue against the critics and return to the bumblebee analogy and examine what's before our eyes. The bottom line is that if we can demonstrate that proteolytic enzymes consumed orally can later be found in the bloodstream, then we know they are absorbed no matter how many experts tell us they can't get there -- even if we don't know exactly how they got there. And in fact, there are a plethora of studies that prove they reach the bloodstream.

When summarizing the argument pro and con on the absorption of non enterically coated proteolytic enzymes in the intestinal tract, I"m reminded of the movie "Chicago". The husband of Kitty (Lucy Liu) says to his wife when caught in bed with two women, "Are you going to believe what you see or what I say?" In the end, it doesn't matter what some experts say, proteolytic enzyme supplements can be seen in the bloodstream,and their benefits can be seen by anyone who uses them.

Fatigue After Eating

And now let me touch on one final topic before concluding this newsletter on the absorption of nutrients in the small intestine: fatigue after eating. This appears to be one of those oxymorons that people have a hard time understanding. How can eating sometimes exhaust us?

We know that we can drink Gatorade or have a Snickers bar for quick energy in the middle of the day. But why is it that when we eat a larger, healthy, full spectrum meal (proteins, carbohydrates, and fats) that we actually feel enervated and sleepy for some time after eating, before the energy kicks in. And the answer is actually quite simple.

Digesting and absorbing food is energy intensive and exhausts the body. It takes energy for the body to produce stomach acid and pepsin. It takes energy for the body to produce the pancreatic enzymes that assist in digestion in the small intestine. And as we've seen in this newsletter, it takes energy to actually absorb proteins and carbohydrates across the enterocytes, into the villi, and on into the bloodstream. All in all, the body expends a great amount of energy getting nutrients into your bloodstream -- enough energy so that you feel exhausted after eating a large meal. And the larger the meal, the more exhausted you feel. It is not until the digested/absorbed nutrients actually make their way through the bloodstream and on into every single cell in your body that you get your energy back. In the end, you gain more energy than you expended, and it is that energy that is used to power your body. But it can take several hours after eating to go from a negative expenditure of energy to a positive intake of energy and balance the scales out.

As a side note, taking supplemental digestive enzymes with your meals significantly decreases the fatigue factor experienced after eating large meals since they relieve your body of so much of its digestive work.

Conclusion

Okay, that concludes our exploration of the small intestine, both digestion and absorption. In our next newsletter we will pick up with the ileocecal valve, the gateway between the small and large intestines. From there we will explore how chyme (actually called fecal matter at this point) moves on through the large intestine and on out through the rectum. We will also explore all of the problems that can occur, including colorectal cancer and some of the options you have in dealing with them -- both medical and alternative.

Date: 04/12/2010
Posted By: Jon Barron
Edited To Fit This Format

The Colon

And now we are ready to conclude our series on the intestinal tract. Several months ago, we began at the top of the tract, in the mouth. We followed our meal step-by-step as it moved on down the esophagus into the stomach where initial digestion began. We then moved into the duodenum and the small intestine where digestion was completed and absorption took place. Now, in this newsletter, we turn to the large intestine, or colon, which absorbs any remaining water in the feces and transfers them to the rectum for excretion. As part of our exploration, we will also explore the various reflexes that move feces into and through the colon. And finally, we will conclude by examining the complicated anal sphincter muscle that controls passage through the anus and then discussing the physiology of defecation. Along the way, we will also explore those things that can go wrong in the colon -- from colon cancer to diverticular disease -- and the options you have to correct them.

Let's begin by looking at the anatomy of the colon, rectum, and anus.

The Colon, Rectum, And Anus

The large intestine (aka the colon or large bowel) is the last part of the digestive system and has two primary functions:

Anatomically, the large intestine begins with an area called the cecum (caecum), which extends on up through the ascending colon, across the body through the transverse colon, then down towards the anus through the descending colon. It ends in an s-shaped "trap" area called the sigmoid colon, which leads to the rectum, and then on out through the anus. In total, it is about five feet (1.5 meters) in length. On average, it is about 2.5 inches wide, but generally starts much wider in the ascending colon and narrows by the time it reaches the sigmoid colon. The pH in the colon varies between 5.5 and 7 (slightly acidic to neutral).

Structurally, the walls of the colon are similar to the small intestine. All of the underlying layers are virtually identical. The serosa (outside covering), muscularis (layer of muscles that control peristalsis), and submucosa (connective tissue), are all the same. The mucosa, the actual surface on the inside of the large intestine, however, is different. Since nutrient absorption is not a factor, there are no villi. Instead, we find a smooth velvety surface with pits dropping deep into the mucosa. The pits are for absorbing water. Note: mucous is secreted by the mucosa to lubricate the colon, but enzymes are not secreted.

The Ileocecal Valve

The ileocecal valve is actually a fold of muscle controlled mucosa located in the cecum between the small and large intestine that serves as the inlet valve of the colon. It acts as a one way valve to allow food wastes to flow from the small intestines into the first part of the colon, the cecum, but prevents waste in the colon from leaking back into the small intestine. It is the distension of the cecum, caused by the chyme entering from the small intestine that actually triggers the closing of the ileocecal valve. The ileocecal valve also has a second related function -- to prevent the contents of the ileum from passing into the cecum prematurely. Note: once chyme (food mixed with digestive juices) passes through the ileocecal valve and enters the cecum, it picks up a new name. It is now designated as fecal matter, and it is still fecal matter if it backs up through a malfunctioning ileocecal valve and reenters the small intestine.

The proper function of the ileocecal valve is to open and close upon demand. When this muscle sticks in the open position, it allows fecal matter back into the small intestine. Not healthy! When the muscle is stuck in the closed position, it causes constipation. The main causes of these two conditions are improper diet and stress; and either condition can seriously affect the body. Alcohol in particular can cause the valve to stick in the open position, resulting in the toxic feeling associated with hangovers.

The Cecum

Shaped like a pouch, the cecum (also spelled caecum) is where the colon begins. It sits on the right side of your body (left when viewed from the front as seen from an anatomy POV) and, as already mentioned, is connected to the small intestines through the ileocecal valve. Its sole function is to receive waste from the small intestine as it pours through the ileocecal valve.

Appendix

Located below the ileocecal valve are the vermiform and retrocecal appendixes. The retrocecal appendix is located inside the cecum and rarely causes a problem. The vermiform ("wormlike add-on") is the familiar appendix that dangles from the cecum and can frequently become inflamed or infected and require surgery. Like the gallbladder, the medical community considers the appendix to be vestigial -- an evolutionary holdover primarily used by ruminants for hard to digest foods, particularly woody foods. The thinking is that in people, It's become less and less important over time -- shriveling to a wormlike vestigial organ that gets infected. However, thanks to surgeons who now save anyone with appendicitis, there's no evolutionary imperative for the appendix to disappear, so it continues. At least that's the medical thinking.

But as with the gallbladder, that thinking may be a misapprehension, and the vermiform appendix may not be as vestigial as is medically assumed. There is now evidence that the appendix may be of significant importance -- that it plays a powerful role in the functioning of the immune system and that it serves as a storage area for beneficial bacteria.

According to a paper published in the Journal of Evolutionary Biology, the appendix serves a dual function. First, it makes, trains, and directs white blood cells. Second, it serves as a type of warehouse or storage compartment for "good bacteria" that boost the immune system when help is required. According to the research, the appendix holds on to reserves of "good bacteria" so that when bad bacteria flourish or a nasty case of diarrhea reduces the colonies of good bacteria, the appendix can send in reinforcements. These bacteria may also influence white blood cells to clear up any infections in the gut. The studies cited in the paper clearly indicate that the appendix does indeed influence white cell function. So once again, it appears medical science may have "vestigialized" an important functioning organ.

The Traffic Junction

The three organs just discussed, the cecum, the ileocecal valve, and the appendix form what can be described as a traffic junction designed to control the flow of waste into the large intestine. Ideally, they should be cleared of waste on a continual basis -- daily at the very least.

This can most easily be achieved by using the squatting position when evacuating your bowels. (If you are not presently visiting a rural village in India where the toilet is a hole in the ground, you can always use a toilet footstool.)

In the squatting position, the left thigh supports the descending and sigmoid colons so as to minimize straining and help squeeze fecal matter on into the rectum for imminent evacuation. In addition, the squatting position helps relax the rectal muscles to facilitate evacuation. Meanwhile, the right thigh presses against the lower abdomen on the right side of the body, thereby "squeezing" the cecum to force waste upwards into the ascending colon and away from the appendix, ileocecal valve, and small intestines.

As a result of waste being pushed up out of the cecum, the appendix is kept free of waste and is unlikely to ever get infected. In addition, pressure from the right thigh also helps the ileocecal valve stay securely closed to guard against any leakage of waste into the small intestine. Finally, as the result of the reduced pressure required for evacuation, the squatting position is a highly effective treatment/preventative for hemorrhoids.

The Large Intestine

Once fecal matter arrives in the cecum, it begins its journey through the rest of the large intestine and on out of the body. The ascending colon, on the right side of the abdomen, is about 25cm (10 inches) long in humans. It extends from the cecum straight up the right side of your abdominal cavity to just under the liver, where it makes a sharp right angle bend to the left (in what is known as the hepatic flexure) and becomes the transverse colon. The ascending colon receives fecal material as a liquid. The muscles of the colon then move the watery waste material forward and slowly begin the absorption of all excess water.

The transverse colon runs straight across the body from right to left, from the hepatic flexure to what is called the splenic flexure (the right angle bend on the left side of the body just below the spleen). As you may remember from our last newsletter, the transverse colon hangs off the stomach, attached to it by the greater omentum. It is about 18 inches long.

The transverse colon is unique among the other parts of the large intestine in one important way: it is mobile. The ascending, descending, and sigmoid colons are pretty much locked into place and do not move noticeably. Not so for the transverse colon. This becomes particularly important later in the newsletter when we talk about prolapsed colons. It should also be noted that colon cancer starts to become more frequent as we enter the transverse colon, with its incidence steadily increasing as we move further along the bowel, peaking when we reach the sigmoid colon and the rectum. One other note on the transverse colon: in some people who are not evacuating their bowels properly, it can become a major storage area for fecal matter. Again, this will be a factor when we talk about prolapsed colons.

The descending colon runs from the end of the transverse colon on the left side of the body, from the splenic flexure to the beginning of the sigmoid colon and is about 12 inches in length. The function of the descending colon in the digestive system is to store food that will be emptied into the rectum. It is also in the descending colon that stools start to become semi solid as they move on to the sigmoid colon.

The sigmoid colon is about 18 inches long and is S-shaped. In fact, sigmoid means S-shaped. It begins just after the descending colon and ends just before the rectum. Stools more or less complete their solidification in the sigmoid colon. Additionally, the walls of the sigmoid colon are muscular and contract to forcefully "move" stools into the rectum.

The rectum begins at the end of the sigmoid colon and is about four to six inches in length. It is defined by its powerful muscles and by the fact that it sits outside the peritoneal lining (the lining of the abdominal cavity). Essentially, the rectum serves as a holding area for fecal matter. Internally, the rectum contains little transverse folds that serve to keep the stool in place until you're ready to go to the bathroom. When you're ready, the stool enters the lower rectum, moves into the anal canal, and then passes through the anus on its way out. Stimulus of the rectum (giving you the urge to go to the bathroom) occurs both internally (which is an involuntary stimulus) and externally (which occurs when you voluntarily squeeze the muscles. Note: by the time they reach the rectum, feces are composed of water salts, desquamated (peeled off or shed) epithelial cells, bacterial decay products, and undigested food (fiber, etc.). Also, the rectum is an excellent absorber. It can be used to instill (insufflate) water, salts, medication, and/or herbs rapidly -- almost as fast as if administered intravenously.

The anus is the end of the trail. Its function is to control the expulsion of feces. The flow of fecal matter through the anus is controlled by the anal sphincter muscle.

Physiology Of Defecation

The feces end up in the rectum via mass peristalsis. Receptors signal distension of the rectum to the brain. This is a conscious perception. The defecation reflex is initiated when parasympathetic (involuntary) stimulation from the spinal cord contracts the longitudinal rectal muscles. This causes pressure to increase in the rectum. Pressure is added to the rectum by voluntary contraction of the abdominal muscles. Parasympathetic stimulation (again involuntary) relaxes the internal sphincter of the anus. This increases the urge to defecate. Finally, the external sphincter is opened by voluntary relaxation, which allows the feces to pass out of the body. This can be postponed by voluntary contraction. This is useful since it allows us to wait for an appropriate time/place to go to the bathroom. However, continually postponing defecation begins to dull the evacuation response over time -- leading to chronic constipation. Then again, voluntary postponement can be overwhelmed by conditions such as diarrhea or long term weakening of the muscles. And finally, sphincter muscles weakened by age, disease, or trauma can cause incontinence (inability to hold feces in). Note: bulky, indigestible fiber acts like a "colonic broom" to move feces through the system more quickly, carrying fat, cholesterol, and carcinogens with it.

Things That Can Go Wrong

According to medical doctors, digestion time (from entering your mouth to passing through your anus) varies depending on the individual. For healthy adults, according to the Mayo Clinic, "It's usually between 24 and 72 hours. After you eat, it takes about six to eight hours for food to pass through your stomach and small intestine. Food then enters your large intestine (colon) for further digestion and absorption of water. Elimination of undigested food residue through the large intestine usually begins after 24 hours. Complete elimination from the body may take several days." That means that, medically speaking, constipation is defined as anything fewer than three bowel movements per week. Or conversely, that normal could be defined as slightly less than one bowel movement every other day.

Quite simply, that's nonsense. It's merely the average elimination time that most doctors see in their patients. But keep in mind, 99% of those patients are eating the standard, fast food, highly processed, low fiber, modern diet. That's neither healthy nor "normal." It's merely what most people do, and most people are unhealthy -- or rapidly moving in that direction. In fact, normal digestion/elimination time is about 24 hours. You literally should have one major bowel movement for every meal you had the day before. You should be passing the waste from yesterday's breakfast when you get up in the morning, or shortly after today's breakfast. Yesterday's lunch should pass around lunchtime and dinner around dinner time. Holding waste in the colon for longer periods of time is one of the single biggest factors in the onset on many major diseases -- not just the colon specific diseases we will discuss below.

Colon Cleansing

Other than eating a healthy, high fiber, largely raw food diet, the single best thing you can do for your overall health and the health of your colon is a semi-annual colon cleanse. Any program designed to improve our health or to eliminate disease from our bodies must begin with intestinal cleansing and detoxification. It is the "sine qua non" of health (literally, "without which, there is not").

Look for a program that addresses all of the following aspects of intestinal health:

Surgical Terminology

A minor digression before we continue! It probably would make sense to define a handful of surgical terms that you are likely to hear from your doctor if you ever have to visit her for any of the conditions below.

Colon Cancer

The most obvious place we see problems associated with not regularly evacuating the bowels is when it comes to colon cancer. Feces remain in the colon for a long time, and carcinogens in feces (which are concentrated to their maximum degree at that point) are currently assumed to explain the prevalence of colon cancer -- second only to lung cancer in the number of deaths it causes each year in the US.

Fecal matter maintains contact with the wall of the large intestine wall for many hours (sometimes for many days if not effectively clearing your bowels on a daily basis). The longer the contact, the greater the problem. The more severe the constipation, the greater the problem. If this fecal matter contains carcinogens ingested with the diet, those carcinogens (some of which are found in grilled meat) have an excellent chance of affecting the wall of the colon -- particularly at places of the longest contact. Not surprisingly, the longest contact and the highest incidence of colon cancer occur in the sigmoid colon, just above the rectum and in the rectum itself.

Societies that eat high fiber, unprocessed diets (that move through the colon more quickly) have far lower incidences of colon cancer, diverticulitis, appendicitis, and coronary artery disease. That said, high fiber diets and proper elimination are not the only factors involved in colon cancer. You can still get colorectal cancer even if you do everything right. Genetics may play a role in up to 10% of colon cancers, for example. Exposure to toxins may also play a factor. Rancid fats in the diet (vegetarian included), too many Omega 6 fatty acids as found in most vegetable oils, and of course, a weakened immune system can all contribute to a higher risk of colon cancer. As always with issues of health, it's a question of odds,not guarantees.

Polyps

A polyp is a projecting mass of overgrown tissue. It looks a lot like an inflated balloon, with the part you tie off attached to wherever It's growing from. Although it is not cancerous itself, virtually all colorectal cancer develops from polyps. When identified during a colonoscopy, polyps are snipped out on the spot thereby eliminating the risk of cancer,from that particular polyp. The same things that cause colon cancer are the things that cause polyps.

Prolapsed Colon (Ptosis)

Ptosis is defined as the abnormal descent (prolapse) of the transverse colon in the abdominal cavity. It is usually associated with the downward displacement of other viscera. It is actually quite common, although the degree to which the transverse colon may prolapse can vary wildly -- from very mild to a full V shape, with the middle of the colon actually dropping down all the way to the pelvis. It also should be noted that it is rare for the transverse colon to prolapse by itself without being accompanied by the prolapse of other abdominal organs. In fact, the term now most commonly used to refer to the condition is enteroptosis (entero referring to the entire intestinal area), which reflects this multi-organ reality. The condition will place pressure on all of the organs under it -- uterus, ovaries, prostate, gonads, and bladder. It will exacerbate any tendency towards constipation and will decrease circulation to all of the organs in the lower half of the abdominal cavity. Also, the more pronounced the condition is, the more likely it is to produce a lower "belly bulge" that won't go away no matter how much weight you lose or scrawny the rest of your body becomes.

The condition is more common in women than men and, in fact, frequent pregnancy is sometimes hypothesized as a contributing factor. But the truth is that although many causes (congenital anomalies, weakness of abdominal muscles from lack of exercise, heavy lifting, etc.) are all suspected, no definitive cause has been found. But there can be no doubt that storing undefecated fecal matter in the transverse colon while awaiting the slow evacuation of the bowels cannot help. In some people, pounds of old fecal matter can be found in the transverse colon waiting a chance to exit the body. And considering that constipation is far more common in women than in men, this would also account for the prevalence of ptosis in women.

How do you treat a prolapsed colon? Actually, medical science has little to offer in the way of help. Surgery is problematic and only rarely helpful. Instead, you need to rebuild your intestinal foundation so as to once again fully support the transverse colon. It is difficult to "fully" reverse a prolapsed colon once it has occurred, but it is possible to "mostly" reverse it -- at least to the point it is no longer visible and no longer noticeably impacts your overall health. Protocol includes:

Crohn's, IBS, Ulcerative Colitis

More Americans are hospitalized for digestive diseases than for any other type of illness. In fact, digestive diseases cost the United States alone an estimated $91 billion annually in health care costs, lost work days and premature deaths. And the bottom line is that virtually every single American will suffer from some form of chronic digestive disorder if they live long enough -- and the rest of the world is following close behind.

Four years ago, I wrote a newsletter on Crohn's disease, IBS, and ulcerative colitis. The information and recommendations still apply today.

Diverticular Disease

Diverticular disease represents one of the great conflicts between the alternative health community and the medical community. For several decades from the early 1900's to the 1940's, the alternative health community vehemently argued that the "modern" diet was creating outpouchings or herniations of the colon. The medical community's equally vehement response was that this was utter nonsense. After all, they argued, "We perform numerous autopsies and never see any evidence of it." And they called alternative health practitioners quacks. Nevertheless, starting in the 50's, they began to take possession of the problem and named it diverticulosis. And as is typical, they gave no acknowledgement to the members of the alternative health community such as John Harvey Kellogg, M.D., who identified the disease almost a half century before they did. Nor was there any acknowledgement that they had missed identifying the condition throughout almost a half century of autopsies -- something worth keeping in mind the next time you hear the medical community say that today's autopsies never provide any evidence of people retaining large amounts of old fecal matter in their colons.

Bragging rights aside, it is now understood by all concerned that many people have small pouches in the lining of their colon that bulge outward through weak spots. Each pouch is called a diverticulum. Multiple pouches are called diverticula. The condition of having diverticula is called diverticulosis. About 10 percent of Americans older than 40 have diverticulosis. About half of all people older than 60 have diverticulosis. The incidence of diverticulosis has increased dramatically from just 10 percent of the adult population over the age of 45 who had this disease in 1952 to an astounding "every person will have many" diverticula, if they live long enough, according to the 1992 edition of the Merck Manual. we've certainly come a long way since the medical community's denial of the first half century.

Comparison Of Digestive Tract Length

Back in September when we started this series on the digestive tract, I announced that as we proceeded, we would be comparing the digestive systems of humans to other animals to see what conclusions could be drawn as to what diet we should eat. And we have done that. we've compared teeth and seen that human teeth are nothing like the teeth of carnivores. we've compared stomachs and seen that once again, the human stomach is very different from that of carnivores and omnivores. In fact, when it comes to teeth and stomachs, humans most closely resemble animals that eat a diet that is mostly comprised of fresh fruit, vegetables, and nuts -- with, in some instances, a bit of raw meat thrown in for good measure.

Is this important?

Yes! The medical community bases its assumptions concerning the human digestive system on the "fact" that it is essentially designed as an omnivore system. But as I discussed in detail in Lessons from the Miracle Doctors (and so far in this series on the digestive tract), this is simply not supported by the evidence at hand. This distinction is not subtle,and not insignificant. Yes, the human body has an amazing ability to adapt to any diet we throw at it -- but not without consequences. And, in fact, many of the diseases we face today are the direct result of not understanding what our systems are designed to handle and the consequences we face as a result.

So, in this newsletter, we reach the last point of comparison: the length of the alimentary canal compared to the length of the body.

An examination of the carnivore intestinal tract reveals a short (relative to the length of their body) tract for fast transit of waste out of the body. The actual length of the carnivore bowel (small and large combined) is approximately 3--5 times the length of the body -- measured from mouth to anus -- a ratio less than half that found in humans. Fast transit of waste for carnivores is essential for two reasons. The faster the transit, the less opportunity for parasites to take hold. Also, meat tends to putrefy in the intestinal tract, so fast transit limits exposure to the byproducts of putrefaction.

As for the herbivore (cows, sheep, etc.) bowel, at 20 - 28 times the length of the body (from mouth to anus), it usually runs almost eight times longer than a carnivore's, since plant matter (unlike meat) is not prone to putrefaction, thus rendering quick elimination moot. Again, not much like us.

As for the bowel of the frugivore (gorilla, orangutan, chimpanzee, etc.), it runs about 10 - 12 times the length of the body from mouth to anus.

So which intestinal tract does the human alimentary canal most closely resemble? As we discussed in our Digestive System Overview, the entire system runs about 30 feet in length from mouth to the anus.

Let's total up the lengths we have identified so far:

That's 29 feet. Add in the mouth, stomach, and rectum and you have a total length of approximately 30 feet. Now compare that to the length of the body (mouth to anus). Why mouth to anus and not head to toe? Because when calculating the body length of four legged animals, we don't stretch out the legs and add them in. We measure from mouth to tail, and so, for a valid comparison, we need to do the same with humans. In any case, mouth to anus is about 2.5 to 3 feet. That gives you a ratio of 10-12 to one. Bingo! It's an absolute match to the frugivore intestinal tract.

What Should We Eat?

So, are we restricted to fruits and nuts? No. In fact, the frugivores we most closely resemble, the wild chimpanzees, periodically eat live insects and raw meat. Among the great apes (the gorilla, the orangutan, the bonobo, and the chimpanzee) and ourselves, only humans and chimpanzees hunt and eat meat on a frequent basis. Nevertheless, chimpanzees are largely fruit eaters, and meat comprises only about 3 percent of their diet -- far less than is found in the typical Western diet.

Is a vegetarian diet automatically healthier? Not necessarily. Some people actually do better when they include small amounts of meat in their diet -- although, to be sure, a balanced vegetarian diet appears to offer some protection against cancer and heart disease. Other factors in our diet, however, affect our health to a much greater degree than whether or not we eat meat. The bottom line is that, ethical questions aside, eating small amounts of meat, chicken, or fish probably comes down mostly to a personal choice. If you choose to, you can include meat in your diet without any significant health problems -- with the following provisos:

Conclusion

we've covered the intestinal tract from mouth to anus over the last five plus months. Specifically, we've explored how we get food into the digestive tract, which organs support digestion, how nutrients are absorbed, and how we process and eliminate waste.

So what useful things have we learned?

Digestive System Information: Natural News 8/15/2012 - Digestive System 101: Here's How It Really Works

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