The Digestive System
Because so many people today are suffering from digestive disorders of one sort or another, a basic understanding of the digestive system is important to the quest for better health. For those interested in spiritual development, an awareness of the digestion processes will be an aid to the attainment of physical and mental balance. This alone can lead to peace and well-being, for mind and body work together as one unit to form one being. What helps the body helps the mind, and vice versa. Awareness of the body is part of a traditional meditative practice. Knowledge of the anatomy and physiology of the body are a big help in giving our bodily awareness form and substance. This can then manifest in our everyday life as awareness of bodily functions and needs which, when satisfied, lead to good health.
The digestive system consists of approximately thirty-two feet of tubing that starts at the mouth and ends at the anus. The tract is a special system concerned with the transport and assimilation of foods and fluids, and the rejection of undigested particles, plus other waste matter, from the body.
The process of digestion occurs in consecutive stages, one blending into the other with no clear subdivisions. The following is a basic classification that is useful in terms of understanding the processes:
1. Ingestion: food is taken into the digestive canal through the mouth, pharynx and oesophagus.
2. Secretion and digestion: enzymes, acids and other chemicals are secreted for the breakdown of food into smaller particles. This process starts in the stomach and continues into the small intestine.
3. Absorption: water and small soluble units are absorbed in the small and large intestines.
4. Assimilation: food is transported via the bloodstream and utilized by the cells of the body. 5. Rejection: undigested particles are expelled from the rectum and anus. This process also removes poisons from the body confines and is part of the general process of cleaning and assimilation that goes on continually.
The body has two holes, the mouth and the rectum. Between them is a hollow tube which stretches from end to end, uninterrupted in its continuity, except for odd valves interspersed between the many sections. The only way food can reach the cells is to be assimilated and absorbed, which requires the complex process described above. Thus try to visualize in yourself this structure passing from end to end, like a pipe, with the rest of the body wrapped around it.
When food particles are ingested, they must be digested, absorbed and assimilated. This transformation is aided by secretions of the stomach, liver, gall bladder and pancreas. The whole process goes on continually, without a break, until all the food ingested is assimilated and all the wastes are disposed of. The process is thus a smooth-flowing continuum, and each part is dependent on the other parts for its efficient functioning. If one step goes wrong the whole process is disturbed and a vicious circle of bad health results. For example, when the digestive juices are not flowing in a balanced and regulated manner, then assimilation and absorption cannot take place. The whole organism is so integrated and dependent on its parts that if one part is not working the whole body suffers.
Food enters the mouth and the process begins, triggered by the sensory mechanism of seeing the food prepared and ready to eat. If the food looks unappetizing, or if the body is not hungry, then the mind and brain do not trigger the digestive juices to function. Therefore eat, when you are hungry, that food which is appeasing and good for you.
Within the mouth the teeth, palate, tongue and salivary glands all function together to make the food into a bolus, a mushy lump which will travel neatly into the stomach. It is important at this stage to chew your food well so that it can be digested more easily. The salivary glands secrete a substance containing the enzyme called ptyalin, which breaks down starch. Therefore the process of digestion really starts in the mouth.
The taste buds are essential for the process of digestion. Not only do they ensure the correct secretion of digestive juices in the mouth, they tell us if the food is health-giving or not. Through them the taste experience is transmitted to the mind thus begetting mental satisfaction. Once the food passes from the mouth it is usually forgotten, unless we cultivate yogic awareness and try to follow it through the many different channels of the body. This can be a rewarding pastime.
Food passes down the oesophagus which secretes a lubricant to aid the passage of food into the stomach.
The swallowing process is quite complex and involves the movement of the tongue to throw the food into the oesophagus, and the cutting off of the air passages to prevent food from passing into the lungs, which is a very uncomfortable sensation. Next time you swallow, close your eyes and try to follow the movements. Become aware of exactly what happens in this common but usually unconscious process.
In the stomach the food is churned and digested by the acids and enzymes secreted by the stomach wall. There are two types of stomach movement taking place during digestion:
1. In the stomach wall, muscles exert a steady and slight pressure which squeezes the food towards the opposite end of the stomach called the pylorus. This movement pushes the food stored in the upper part of the stomach towards the lower end, where it enters the small intestine.
2. A vigorous contracting movement mixes and churns the food with digestive juices and pushes it into the duodenum, the first part of the small intestine. The gastric juices include hydrochloric acid and enzymes such as pepsin, lipase, rennin (to break down milk), protein and fats. The stomach secretes hormones whose exact functions are still not fully known, such as gastrin. It also secretes mucin, which forms a barrier to keep the stomach from digesting itself. This substance prevents ulcers forming on the wall of the stomach. In the duodenum the food is further digested by juices from the liver and pancreas which pour down a common duct (tube).
The pancreas is a large gland which lies behind the stomach and gives two secretions:
1. Insulin, which pours into the blood stream and helps the blood glucose to be taken into body cells after absorption takes place.
2. Pancreatic juices which contain:
a) alkaline salts to naturalize the potent gastric acids
b) lipase which splits fats
c) amylase which splits starch to maltose
d) maltase which changes maltose to glucose (the basic body sugar)
e) trypsin and chymotrypsin which split protein
f) rennin for milk.
The liver is a highly complex organ with many different functions. One of the most important of these is the production of bile which is stored in the gall bladder just under the liver. It is this compound which gives faeces their characteristic colour and smell. It allows the fats of the food to be absorbed in the form of cholesterol (an important product in the correct quantity, but not in excess), vitamins D and K. The liver also stores iron, vitamins B12, A, D, and glucose for use in emergencies, fats and other substances.
The liver breaks down, or detoxifies, many of the poisons and chemicals entering and made by the body. It is concerned with destruction of red blood cells, as well as the manufacture of protein and other important substances. The liver purifies our blood and maintains the body processes. It is such an important organ that we cannot do without it.
After leaving the duodenum, food passes into the jejunum, another part of the small intestine. This tube of muscle (over twenty feet long) is not really small, but it is thinner than the large intestine, which is short.
Food is continually being digested and passed down the intestines. A continual churning motion allows all of the food to come into contact with the muscle wall, where absorption takes place of substances such as amino acids (proteins), sugars, minerals, glycerol, fats, vitamins and glycerides. Capillaries and lacteals absorb these different substances and transport them into the main part of the bloodstream for distribution to the whole body. It is the cells of the wall that actually do the work of carrying digested food products into the blood.
The large intestine is approximately six feet long. Its function is to absorb water and salts into the blood so that the body does not lose too much of these valuable substances. By drying out faeces we retain fluids and salts, and allow stool to form. Mucus is secreted by the muscle walls and this naturalizes and lubricates the faeces, acting as a barrier and defence against bacteria. The sigmoid part of the large intestine stores the faeces until there is enough to stimulate the desire to defecate.
Faeces are mainly the residue from the small intestine and contain:
a) residues of indigestible material in food, such as the skins of fruit and vegetables (mainly cellulose)
c) intestinal secretions, including mucus
d) white blood cells
e) cells from the walls of the intestine
f) large numbers of bacteria, which make up one third of the total solids
g) inorganic material (10-20 per cent)
Note: very little digestible material is present.
Defecation is a complex reflex act. As the passage of faeces into the rectum distends the muscular tube, signals are sent to the conscious and unconscious parts of the brain. This brings about a conscious voluntary decision to inhibit or permit reflex evacuation. If we are relaxed, the process occurs all the more efficiently.
The parasympathetic system, which is concerned with relaxation of the whole body, allows the sphincters to open and the muscle wall to contract, propelling faeces out of the anus.
A great many disorders are connected directly to malfunction of the digestive system. In this way the digestive system has a direct influence on one's daily life. You must have noticed for yourself that when you are experiencing digestive troubles, you tend to be pessimistic and easily irritated. Conversely, a healthy digestive system allows one to be happy and free from pain, worry and suffering, to be cheerful and optimistic.
Yoga is the way to bring about a relaxed, efficient and harmonious digestive system. It is the key by which the body systems can be tuned to a state of good health. With yoga as a guide, we can come to a complete understanding of what proper digestion can mean to our whole way of life. A good digestive system means energy and vitality; it reflects a positive life style.