(11).DIGESTIVE SYSTEM:

 1. The function of the digestive system is to prepare food for intake by body cells. Nutrients must be broken down by mechanical and chemical means into molecules that are small enough to be absorbed into the circulation. Within cells, the nutrients are used for energy and for rebuilding vital cell components. Digestion takes place in the digestive tract proper, also called the alimentary canal or gastrointestinal (GI) tract. Also contributing to the digestive process are several accessory organs that release secretions into the small intestine. Food is moved through the digestive tract by peristalsis, ( wavelike contraction) of the organ walls. Peristalsis also moves undigested waste material out of the body.

 Digestion begins in the mouth, where food is chewed into small bits by the teeth. In the process of chewing, or mastication, the tongue and the palate, the roof of the mouth, help to break up the food and mix it with saliva, a secretion that moistens the food and begins the digestion of starch. The moistened food is then passed into the pharynx (throat) and through the esophagus into the stomach. Here it is further broken down by churning of the stomach as it is mixed with the enzyme pepsin and with powerful hydrochloric acid (HCl), both of which break down proteins. The partially digested food passes through the lower portion of the stomach, the pylorus, into the first part of the small intestine, the duodenum. As the food continues through the jejunum and ileum, the remaining sections of the small intestine, digestion is completed. The substances active in digestion in the small intestine include enzymes from the intestine itself and secretions from the accessory organs of digestion. 

The digested nutrients, as well as water, minerals, and vitamins, are absorbed into the circulation, aided by small projections in the lining of the small intestine called villi. The Undigested food, water, and digestive juices pass into the large intestine. This part of the digestive tract begins in the lower right region of the abdomen with a small pouch, the cecum, to which the appendix is attached. The large intestine continues as the colon, a name that is often used to mean the large intestine because the colon constitutes such a large portion of that organ. The colon travels upward along the right side of the abdomen as the ascending colon, crosses below the stomach as the transverse colon, then continues down the left side of the abdomen as the descending colon. As food is pushed through the colon, water is reabsorbed and stool or feces is formed. This waste material passes into the S-shaped sigmoid colon and is stored in the rectum until eliminated through the anus.

The Accessory Organs:

 The liver is a large gland with many functions. A major part of its activity is to process blood brought to it by a special circulatory pathway called the hepatic portal system. Its role in digestion is the secretion of bile, which breaks down fats. Bile is stored in the gallbladder until needed. The common hepatic duct from the liver and the cystic duct from the gallbladder merge to form the common bile duct, which empties into the duodenum. The pancreas produces a mixture of digestive enzymes that is delivered into the duodenum through the pancreatic duct.

eating balance diet food, fruits and vegetables is very important.

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