Anatomy & Physiology

Anatomy & Physiology Study Guide • The intestinal mucosa bears transverse folds called plicae circulares, and small projections called intestinal villi. These folds and projections increase the surface area for absorption. Each villus contains a terminal lymphatic called a lacteal. Pockets called intestinal glands are lined by enteroendocrine, mucous, and stem cells. • Intestinal juice moistens chyme, helps buffer acids, and holds digestive enzymes and digestive products in solution. • The duodenal (submucosal or Brunner) glands of the duodenum produce mucus, bicarbonate ions, and the hormone urogastrone. Masses of lymphoid tissue called aggregated lymphoid nodules (Peyer patches) are located in the ileum near the entrance to the large intestine. • Initiated by stretch receptors in the stomach, gastroenteric reflexes stimulates awareness and secretion along the entire small intestine. In addition to triggering the relaxation of the ileocecal valve. • The wall of the duodenum is penetrated by the pancreatic duct. Within each lobule of the pancreas, ducts repeatedly branch before ending in the pancreatic acini (blind pockets). • The pancreas has two functions: endocrine (secreting insulin and glucagon into the blood) and exocrine (secreting pancreatic juice into the small intestine). Pancreatic enzymes include carbohydrases, lipases, nucleases, and proteolytic enzymes. • The liver performs metabolic and hematological regulation and produces bile. The bile ducts from all the liver lobules come together to form the common hepatic duct. Then the common hepatic duct meets the cystic duct to form the common bile duct, which then empties into the duodenum. • The organ’s basic functional unit is the liver lobule. Hepatocytes form irregular plates and are arranged similarly to the spokes of a bicycle wheel. Bile canaliculi carry bile to the bile ductules, which lead to portal areas. • Bile salts break apart large drops of lipids during emulsification. This makes the lipids accessible to the lipases secreted by the pancreas. • The primary main organ responsible for the regulation and composition of the circulating blood is the liver because the blood leaving the absorptive surfaces of the digestive tract flows directly into the liver before it enters the systemic circulation. The liver regulates metabolism as it removes and stores excess nutrients, vitamins, and minerals from the blood; mobilizes stored reserves; synthesizes needed nutrients; and removes waste products. • The liver’s hematological activities include the monitoring of circulating blood by phagocytes and antigen-presenting cells; the synthesis of plasma proteins; the removal of circulating hormones and antibodies; and the removal or storage of toxins. • The liver synthesizes bile, which is composed of water, ions, bilirubin, cholesterol, and bile salts (an assortment of lipids). • The gallbladder stores, modifies, and concentrates bile. • Neural and hormonal mechanisms coordinate the activities of the digestive glands. Gastrointestinal activity is stimulated by parasympathetic innervation and inhibited by Achieve Page 327 of 368 ©2018