The Digestive System
12 Oct 2021 HYN Himalayan Yoga Academy
Digestive System is also known as alimentary or gastro-alimentary system. It provides nourishment to all the body cells from the external environment. Food intake; its digestion, absorption and assimilation; water balance; elimination of residue; waste products and poisonous substance are the main functions of this system. The system includes gastrointestinal tract (alimentary canal), salivary glands, and portions of liver and pancreas. The alimentary canal is a continuous tube. It consists of mouth( buccal cavity), throat (pharynx), esophagus, stomach , small intestine, large intestine(colon), rectum, and anal canal, ending in the anus.
The oral cavity (mouth ) is made up of a small outer portion ( vestibule) between the teeth and the lips and the inner major part between the teeth and the lips and the inner major part between the teeth and the tongue. Roof of the mputh consists of a hard and sft palate. Soft palate helps in swallowing, sucking , blowing and producing sound. The uvula hangs down from the soft palate.
The tongue is a muscular organ. It helps inn chewing , swallowing , speaking, and tasting. Pharynx is a muscular tube, which leads to esophagus and ends into the stomach. Digestinve glands are situated in the w all of stomach. They secrete juices, containing enzymes, which break downs the food particles into simple soluble substances. Carbohydrates (sugar starch), proteins, and fats are three important nutrients of our food. They are digested due to chemical actions of enzymes. The digested food is easily absorbed through the inner wall of the small intestine into the blood capillaries, Pancreas and liver also helps in digestion by supplying the pancreatic juice and bile respectively . The absorbed food particles are carried to the liver and then into the general circulation.The longitudinal and circular muscles of the alimentary wall contract alternately and produce wave like periodic movements of the tract. The involuntary muscular movement is known as peristalsis. Peristalitic movements are controlled by medulla oblongata. This peristaltic movement pushes the food forward along the tract during the process of digestion.
More on Digestive System
The stomach opens into the duodenum,which further leads to small intestine. The small intestine is about 5 metres long. It joins large intestine(colon) , which is about 1.5 metres long and has got three distinct parts, viz, ascending, transverse and descending colon. Lasts parts of the large intestine are known as rectum and anal canal, which open to the external environment through anus. The colon conents are greatly influenced during uddiyan, nauli , and basti kriyas.
Most of the digested food is absorbed in the small intestine. The large intestine absorbs mainly sodium along with the large quantities of water. This makes the fecal material dry. In turn, potassium is transported from the blood capillaries into the lumen of the large intestine to keep feces moisturized. Repeated enemas or diarrhea may lead to serious loss of potassium in the body and therefore one may experience weakness in the muscles. The large intestine also absorbs some of the products synthesized by the bacteria. For example, small amounts of vitamins, which are synthesized by bacteria in the large intestine, are absorbed by the large intestine itself.
Undigested, unwanted and toxic residues of food are passed on to the rectum and then eliminated through the anus during the process of defecation. This evacuation of the bowel is assisted by a deep inspiration followed by closure of the glottis and contraction of the abdominal and chest muscles , causing a marked increase in intrathoracic pressure. There is a sudden rise in the blood pressure. This is followed by a fall in the blood pressure due to decreased venous return(returning blood) to the heart.
Internal and external anal sphincters guard anus. The internal anal sphincter is made up of smooth muscles. The external anal sphincter is a skeletal muscle, which can be controlled voluntarily.
The smooth muscles of the digestive parts are involuntary muscles, which are not working under our will. Major autonomic nerve of the gastrointestinal tract(GIT) is the vague nerve, which sends branches to the stomach, small intestine and upper portion of large intestine. This nerve is composed of efferent parasympathetic fibres and many afferent fibres(conveying information to the nervous system) from receptors and nerve plexuses in the GIT. In short, the activity of smooth muscles and exocrine( digestive) glands are controlled by the automatic nervous system and the internal nerve plexus as well as the hormones secreted by GIT itself. Gastrointestinal receptors initiate reflexes and the information is conveyed to the central nervous system(CNS). Short reflexes bring about self-regulation in the tract, Strong reflexes, however , bring CNS into action and our attention is drawn. For example, the sight of food initiates reflex, which involves CNS and one thinks abouot the food items and their selection. Complex behavioral change due to emotions and moods can influence the GIT through CNS and the appetite may be increased or reduced.
Sometimes, we become aware of a few sensations like pressure, pain , temperature, or burning in the abdominal region. This is mainly due to various visceroreceptors situated along the GIT . When they are stimualtd becaude of strectching, pressure,or the chemical action, the strong sensory impulses are sent to CNS and our attention is drawn. Hunger and appetite are such sensations coming from the stomach =. The appetite center lies in the lateral hypothalamus , which on stimualation increases the food intake. The medial hypothalamus contains satiety centre , which on stimulations inhibits the food intake.
The entire digestive and other parts are properly held and protected by means of very strong muscles that form the wall of the belly. The abdominal wall prevents displacement of the stomach,intestine,or any other organ in the abdomen. The abdominal wall also provides mechanical support to the abdominal viscera as it contains strong rectus abdominus muscles. This helps to maintain the tone of the involuntary muscles of the abdominal organs.
From yoga point of view
- Once the liquid food materials enters the stomach, it will be digested and later on absorbed in the small intestine within half an hour. Solid food (e.g.-lunch) will take 2-2.5 hours for main digestion and 4-6 hours hours for complete absorption. That is why yoga practices should be done either in the morning or in the evening with an empty stomach.
- The central nervous system has no direct control on the digestive function but the appetite and satiety centers lie in the hypothalamus . Our emotional balance and behavior are also connected by the hypothalamic centers. It has been found that even the muscular tone of the smooth muscles of the visceral parts is affected due to our emotional status(e.g., anger, hatred, and irritation). Thus our digestion is affected due to our thinking style, tense ,and unsatisfied mind and the negative approach. This cause indigestion, acidity, and gastric troubles. If the digestive function is disturbed, our health is also affected. It is therefore advisable to maintain mental peace and balance all the time, with the positive approach, contentment and happiness , which can also be achieved through yoga.
- Almost all the asanas as well as kriyas influence stomach,colon, urinary bladder and the liver.
- Dhauti is mainly related to esophagus and stomach while basti is concerned with the anus, rectum, and the colon.
- The external sphincters of the anus are contracted and relaxed alternatively in Ashwini mudra.