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What is it?

The digestive tract, one of the largest of all body systems, extends approximately 30 feet long and extends as a long continuous tube, from mouth to anus! This system is unique in that it is strictly speaking "outside the body".  That is, it's long continuous tube communicates with the outside world. The diagram to the right shows this.

The digestive system is divided into regions that specialize in the process of digestion. The tract is primarily composed of a layer of cells, that secrete digestive juices and mucous as well as absorb nutrients, surrounded by muscle. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. We'll describe the digestive process in detail.

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.  Moving constantly and slowly, the digestive tract and it's accessory organs of digestion (the liver, gallbladder and pancreas) are faced with the task of converting all the foods we eat (from apples to zuchinni) into energy that supports and supplies the brain, the heart and the entire body. Impressively, the digestive tract can digest and absorb about 95 percent of nutrients, water, and electrolytes eaten (that is if we eat foods that don't harm it's environment).

In many senses, the digestive system resembles our car's gas tank. The food we eat is the fuel or gas that the digestive system (or fuel tank), converts into combustible power and energy needed to make our muscles move, carry out bodily functions, and repair and rebuild tissue. The digestive tract also functions as an immune organ, serving as a protective barrier to ingested toxins, allergens, and pathogens (bacteria, parasites, viruses, and fungi) that could otherwise cause disease.

The process of digestion begins with chewing. Chewing breaks up food into smaller pieces that can be swallowed without choking. The salivary glands secrete a mucous solution into the mouth that moistens and lubricates food particles. Saliva contains an enzyme that begins to digest carbohydrates. As food particles begin to dissolve, they react with the chemoreceptors in the mouth, giving rise to the sensation of taste.

The Diaphragm

The diaphragm is a dome-shaped sheet of skeletal muscle that separates the abdominal and thoracic (the area of the chest containing the heart and lungs) cavities. It is the principal muscle of respiration.

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 nervous system.
 

How Do We Digest Food?

Food contains many large molecules such as proteins and complex carbohydrates, which are essentially foreign materials to the body's tissues, and as such, constitute antigens. Proper digestion of food is extremely important, for without adequate breakdown, the body's immune system would be activated against your very nourishment, with far reaching consequences. Additionally, a damaged or leaky gut wall will also lead to increased penetration into the bloodstream of these "dietary antigens."

The human diet is made up of foods consisting of nutrients (vitamins, minerals, carbohydrates, proteins, and fats), residues (vegetable fiber), water, and unfortunately with processed foods, many foreign chemicals, some of which, do not even occur in nature. Also consumed are a plethora of various molecules found in natural foods and herbs, including flavonoids, polyphenolics, volatile oils, resins, tannins, saponins, etc.

Most vitamins and chelated minerals are absorbed into the bloodstream without change. Larger molecules must be broken down to effect healthy utilization of their value, and prevent potentially severe results if they are not. Apart from physical maceration which occurs in the mouth, the rest of the digestive job is left to the actions of enzymes, acids, and salts, all of which must occur in the right amounts and in the right environment for them to work.

Carbohydrates are provided from starchy and sugary foods, and are the main source of energy for the body. With adequate digestion, they are broken down to glucose, fructose, and galactose. Complex carbohydrates provide for a gradual timed release of these energy molecules. Consumption of refined sugars and white flower, on the other hand, impact the body by producing an abnormally high level in the bloodstream of these simple sugars (hyperglycemia hyperglycemia), such as produced in inadequately controlled diabetes mellitus, producing thirst, the passing of large amounts of urine, glycosuria (glucose in the urine), and ketosis (an accumulation of ketones in the body).

The pancreas in the non-diabetic, seeing the abnormally high level of glucose, then secretes more insulin, which promotes the absorption of glucose into the liver and into muscle cells, where it is converted to energy and into fat cells for storage. In the liver, glucose is stored as glycogen, which is reconverted back to glucose in response to stress or exercise. The problem begins with there now being too much insulin produced due to the abnormal dumping of glucose into the bloodstream. The insulin excess, then converts all the glucose, resulting in hypoglycemia (an abnormally low level of glucose in the blood) resulting in symptoms including sweating, weakness, hunger, dizziness, trembling, headache, palpitations, confusion, and sometimes double vision. Behavior is often irrational and aggressive and movements are uncoordinated. The symptom of hunger, often resulting from the consumption of 'empty calories', which can then prompt the individual to consume more sugar, starting another cycle. Additionally, this practice produces a lot of stored energy that needs to be dissipated, leaving the body tense.

Proteins, found abundantly in meat, fish, eggs, cheese, peas, beans, and lentils, are used primarily for the construction and repair of body tissues, and to form enzymes, hormones, and other chemical mediators used to control and regulate the body. Proteins are broken down progressively into polypeptides, peptides, and finally amino acids.

Fats (also known as lipids and includes oils) are found in meat, dairy products, and plant foods such as nuts, avocados, olives, etc., also provide energy and some of the materials for cell building and maintenance, especially nerve cells and skin tissue. Fats also carry the fat-soluble vitamins A, D, E and K. Fats are digested down to glycerol, glycerides, and fatty acids, by enzymes called lipases which are secreted by the pancreas and intestine.

Minerals are not digested, but rather chelated (combined with amino acids) for the purpose of absorption. Mineral ions, like iron, calcium, and zinc are relatively insoluble and best assimilated when presented from natural sources such as the animal tissues like eggs and dairy foods. Additionally, mineral chelation can only happen in an appropriate acid environment, and therefore, advertisements promoting antacid products with the 'benefit of calcium' are without merit, the acid environment necessary for proper chelation having been quenched by the alkaloids of the antacid. Of course, the antacid manufacturers would rather not tell you this, preferring that you take their product before 'every meal' to prevent acid indigestion (an oxymoron). This practice would be very dangerous and destructive. Even the AMA states: "Antacid drugs should not be taken regularly except under medical supervision as they may suppress the symptoms of a more serious disorder and provoke serious complications."

True hyperacidity, can be treated with herbs to reduce stomach acid production, such as slippery elm, meadowsweet, marshmallow, and Iceland moss. They may be usefully augmented by relaxants such as chamomile, lemon balm and peppermint in tea form. Dietary reform consisting of avoidance of refined foods, junk foods, coffee, and in some cases avoidance of acrid principals found in the hot spices such as cayenne, ginger, mustard, peppers, horseradish, and raw onions and garlic will reduce acid production by the stomach. Keep in mind, however, that hyperacidity is a sign of a more significant underlying problem. Bitter digestive remedies are sometimes discouraged since their reflex action stimulates acid production, however, one must keep in mind that unlike the acrid constituents, the bitters stimulate the totality of digestive activity, including secretions of protective fluids, such as bicarbonate from liver and pancreas and from the Brunner's glands.

The process of digestion begins in the mouth, or perhaps in the mind, where anticipation of your meal can stimulate salivation. The teeth and tongue perform mechanical maceration, and taste buds generate signals to the salivary glands. Saliva contains enzymes that break down carbohydrates. Sour tastes, particularly citric acid (found in fruit) stimulates the reflex to saliva secretion and the production of the hormone gastrin (which gets the whole digestive machinery into motion), and additionally ensures a beneficial alkaline environment. (citric acid quickly breaks down into bicarbonates, and hence is surpassingly an alkaline food).

From the mouth, food passes into the pharynx, which then pushes it into the esophagus which then pushes it into the stomach. This motion, as performed throughout the digestive tract, is called peristalsis. In the stomach, food is mixed with gastric juices secreted in the stomach lining, first, in the upper portion which is relatively alkaline (saliva is alkaline which is swallowed with the food). As the food continues to break down, the bottom half of the stomach begins to open and pepsin (an enzyme that breaks down protein) along with hydrochloric acid (which kills bacteria and other organisms and provides the necessary low pH for the pepsin to work), are secreted along with enzymes, salts, and intrinsic factor (which is essential for the absorption of vitamin B12 in the small intestine). The stomach lining also contains glands that secrete mucus, which provides a barrier to keep the stomach from digesting itself. The stomach wall consists of longitudinal and circular muscles which keep the contents mixed, and a separate muscle forming a ring called the pyloric sphincter where the stomach empties into the duodenum. The stomach lining also contains a vast network of blood vessels and capillaries.

Eating too fast, not chewing food properly, and drinking too much liquids with the meal (dilutes digestive enzymes and acids) are all counter productive to adequate digestion. Additionally, different types of foods require different digestive environments and therefore proper food combining (or not combining) is required for proper digestion. Melons should not be combined with anything, or otherwise they can ferment in your digestive tract. Vegetables should not be combined with fruits, and fruits shouldn't be combined with a protein meal. Therefore lunch and dinner which often include proteins, could be accompanied by the very important vegetables (such as a salad or cooked cruceriferous vegetables) which need to be included with each daily diet. Take fruit for dissert only after your meal has had time to digest. Or better yet, save fruit for the mornings (or in-between meals for a pick-me-up snack), as they are cleansing and stimulating, whereas vegetables are 'body building' and appropriate for the evening and night. As far as snacks are concerned, nuts are excellent, and can be combined with fruits, but start on the nuts first, as they are harder to digest.

When the food has been converted to a semi-liquid consistency, it is passed from the stomach to the duodenum. The liver produces bile salts and acids, which are stored in the gallbladder and then released into the duodenum. These salts and acids help break down fats. The pancreas also releases digestive juices into the duodenum, which contain enzymes that further breakdown carbohydrates, fats, and proteins. The final breakdown stages are completed in the small intestine, carried out by enzymes produced by glands in the lining of the intestine. The result of a successful digestion, is food converted into a safe (non-antigenic) and useful pabulum.

A note about fats: the body is mostly water, yet the fat (lipids) in your food must be moved throughout your body, and you know that oil and water don't mix, so various emulsifying strategies are adopted, using cholesterol, lecithins, and bile, to form complexes with the lipids. As the fats are taken up by the tissues throughout the body, these complexes become increasingly cholesterol-, and then protein-rich, moving from what are termed very-low density lipoproteins (VLDL's) through to LDL's and to high-density lipoproteins (HDL's). The relative quantity of the later in the blood is a fair measure of the efficiency with which fat transfer has occurred, and is thus a positive indicator for the prevention of fat deposition in the blood vessels (contributing to atherosclerosis and cardiovascular disease).

How Is the Digestive Process Controlled? Hormone Regulators

A fascinating feature of the digestive system is that it contains its own 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):

• Gastrin causes the stomach to produce an acid for dissolving and digesting some foods. It is also necessary for the normal growth of the lining of the stomach, small intestine, and colon.
• Secretin causes the pancreas to send out a digestive juice that is rich in bicarbonate. It stimulates the stomach to produce pepsin, an enzyme that digests protein, and it also stimulates the liver to produce bile.
• CCK causes the pancreas to grow and to produce the enzymes of pancreatic juice, and it causes the gallbladder to empty.

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.

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