Digestive System

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7.4     The digestion of food begins in the mouth with the three pairs of salivary glands and continues in the stomach and the small intestines. The smell, and even the thought of food causes these glands to increase their production of saliva and our mouths start watering. Saliva contains enzymes that breakdown starches and other complex carbohydrates in food. As a person chews, food is broken into small pieces and mixed with the saliva, which moistens it and/or makes it slippery for easier swallowing. Proper chewing is essential for optimal digestion. In addition to stimulating the digestive juices in the saliva, proper chewing breaks down food, massively increasing the surface area available for contact with digestive juices. This increases the efficiency of digestion by giving stomach acid and digestive enzymes the opportunity to penetrate the food and do the digestive work. Each mouthful should ideally be chewed to a cream before swallowing.

  The Stomach

7.5     After food is properly chewed and swallowed, it passes through a muscular 25 cm. long food pipe (oesophagus or gullet) and enters the J-shaped muscular stomach. The stomach wall has three muscle layers and a mucus membrane that line it. An average adult holds about one litre of mixed food. The glands in the stomach lining secrete a variety of enzymes including pepsin, hydrochloric acid and other chemical compounds. These secretions aid in digesting the food and are collectively called gastric juices. Most of the protein and carbohydrates in the food are broken down in the stomach. The churning action of the stomach muscles furthers the digestion process by mixing the food and gastric juices. After about 3-5 hours, depending on the type, the food becomes a liquid called chyme. The chyme then passes into the small intestines.

 The Intestines

7.6         The intestines are among the most amazing organs in our body, beautifully organised to do hundreds of things to the food we eat to keep alive. Intestines, about 3 metres long, stretch from the lower end of the stomach to the anus, which is the lower opening of the digestive tract. Most of the wall of the intestines consists of muscle fibres, so that the intestines can work on the food that goes through them. The intestines mix the food with certain chemicals while passing them along. Intestines are divided into two sections called the small intestine and large intestine. The small intestine consists of numerous loops, Each loop holds a bit of food and works on it, that is, churning and digesting it for about 30 minutes. Then the food is passed on to the next loop. The walls of the intestines contain nearly 20,000,000 glands that secrete many juices, which help the food to be digested and absorbed in the small intestine. The large intestine eliminates undigested wastes from the body. Billions of bacteria in the intestines breakdown the coarser parts of the food we eat, such as the skins of fruit, and extract valuable substances that the body needs. The bloodstream takes away absorbed food from the small intestine and supplies the nutrients, thus absorbed, to different tissues of the body.

  The Small Intestine

7.7     The digestion of proteins and carbohydrates continues and the digestion of fats occurs in the portion of the small intestine close to the stomach on the partly digested food by the pancreatic juice, the intestinal juice and bile. The pancreatic juice pours into the small intestine through a tube or duct. The intestinal juice is produced by the walls of the small intestine. And bile is produced in the liver, stored in the gall bladder, and flows into the small intestine through a duct. Bile helps in breaking down fats.

 7.8     The remainder of the small intestine performs the critical function of absorbing the digested food. The walls of the small intestine are covered with tiny projections called villi. Each villus contains tiny (capillaries) blood and lymph vessels and is covered by hair-like projections called microville. The presence of the villi and microville increase the total area to larger than a tennis court for nutrient absorption. Nutrients from the completely digested food move from the small intestine into the blood stream through the capillaries, where they are transported to the cells of the body for nourishment.

  The Large Intestine (Colon)

7.9     Undigested food moves into the large intestine, where importantly water is absorbed from the waste and returned to the bloodstream. Almost no digestion or food absorption takes place in the large intestine. Peristalsis (wave like alternate contraction and relaxation) moves the solid digestive waste as well as other body wastes such as used hormones, toxins and cholesterol called faeces, through the large intestine to the rectum. Here it is stored briefly and then eliminated through the anus opening.