Liver and Digestive System

The digestive system processes that food broken down into molecules that are small enough to enter body cells. The passage of these smaller molecules through the plasma membranes of cell lining the stomach and intestines and then into the blood and lymph is termed absorption. Two groups of organs compose the digestive system: 1. The Gastrointestinal tract (GIT) or Alimentary canal is continuous tube that extends from the mouth to the anus through the ventral body cavity, which includes mouth, most of the pharynx, esophagus, stomach, small intestine and large intestine. The length of the GI tract from a cadaver is 9 m (30 ft); 2. The Accessory digestive organs are the teeth, tongue, salivary glands, liver, gallbladder and pancreas. The food we eat contains a variety of nutrients, which are used for building new body tissues and reparing damaged tissues.

Overall, the Digestive Systems performs six basic processes:

1. Ingestion: This process involves taking foods and liquids into the mouth (eating).

2. Secretion: Each day, cells within the walls of GI tract and accessory digestive organs secrete a total of about 7 liters of water, acid , buffers, enzymes into the luman of the tract.

3. Mixing and propulsion: alternating contraction and relaxation of smooth muscle in the walls of GI tract mix food and secretions and propel them toward the anus. this capability of the GI tract to mix and move material along its length is termed motility.

4. Digestion: mechanical and chemical processes break down ingested food into small molecules. In machanical digestion the teeth cut and grind food before it is swallowed, and then smooth museles of the stomach and small intesine churn the food. As a result, food molecules become dissolved and thoroughly mixed with digestive enzymes. In chemical disestion the large carbohydrate, lipid, protein and nuclec acid molecules in food are split into smaller molecules by hydrolysis. Digestive enzymus produced by the salivary glands, tongue, stomach, pancrea, and small intestine catalyze these catabolic reaction. A few substances in food can be absorbed without chemical digestion. These include amino acid, cholesterol, glucose, vitamins, minerals and water.

5. Absorption: The entrance of ingested and secreted fluids, ions, and the small molecules that are products of digestion into the epithelial cells lining the lumen of the GI tract is called absorption. The absorbed substances pass into blood or lymph and circulate to cells throughout the body.

6. Defecation: Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI tract and digested materials that were not absorbed leave the body through the anus in a process called defecation. The eliminated material is termed feces.