The Liver and Bile Secretion PDF

# The Liver and Bile Secretion The liver is a large gland located in the upper right portion of the abdomen. It has a variety of functions which are described in various chapters. The liver's exocrine functions are directly related to the secretion of bile. ## Bile Bile contains: * Bicarbonate i...

# The Liver and Bile Secretion The liver is a large gland located in the upper right portion of the abdomen. It has a variety of functions which are described in various chapters. The liver's exocrine functions are directly related to the secretion of bile. ## Bile Bile contains: * Bicarbonate ions * Cholesterol * Phospholipids * Bile pigments * Organic wastes * Bile salts Bile salts help neutralize acid from the stomach and solubilize dietary fat. ## Bile Secretion and Storage Bile is secreted by the liver into small ducts that join to form a single duct called the common hepatic duct. Between meals, secreted bile is stored in the gallbladder, a small sac underneath the liver. The gallbladder concentrates the organic molecules in bile by absorbing salts and water. During a meal, the gallbladder contracts and releases bile into the duodenum via the common bile duct. The gallbladder can be surgically removed without impairing bile secretion by the liver. ## Absorption in the Small Intestine In the small intestine, monosaccharides and amino acids are absorbed by specific transporter-mediated processes in the plasma membranes of the intestinal epithelial cells. Fatty acids enter these cells by diffusion. Most mineral ions are actively absorbed by transporters, and water diffuses passively down osmotic gradients. ## Motility of the Small Intestine The motility of the small intestine mixes the luminal contents with secretions, brings the contents into contact with epithelial surface for absorption, and moves the material toward the large intestine. ## Large Intestine The large intestine stores undigested material, concentrates it by absorbing salts and water, and expels the feces. ## Fluid Consumption and Absorption The average adult consumes about 800 g of food and 1200 ml of water per day. An additional 7000 ml of fluid from salivary glands, gastric glands, pancreas, liver, and intestinal glands is secreted into the gastrointestinal tract each day. Of the 8 L of fluid entering the tract, 99 percent is absorbed; only about 100 ml is normally lost in the feces. Almost all the salts in the secreted fluids are also reabsorbed into the blood. The secreted digestive enzymes are themselves digested, and the resulting amino acids are absorbed into the blood. # Overview of the Gastrointestinal System This completes our overview of the gastrointestinal system. The gastrointestinal system's major task is digestion and absorption. Subsequent sections of the chapter will then describe, organ by organ, regulation of the secretions and motility that produce the optimal conditions for digestion and absorption. A prerequisite for this physiology, however, is a knowledge of the structure of the gastrointestinal tract wall.