Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 323 The food contains large organic molecules; many of them are insoluble. The digestive system first breaks down the physical structure of the ingested material and then proceeds to disassemble the component molecules into smaller fragments. This disassembly eliminates any antigenic properties; thus, the fragments do not trigger an immune response after absorption. Cells absorb the molecules released into the bloodstream and either break them down to provide energy for the synthesis of ATP or use these molecules to synthesize carbohydrates, proteins, and lipids. Digestive enzymes secreted by the salivary glands, tongue, stomach, and pancreas are mixed into the ingested material as it passes through the digestive tract. Carbohydrates are broken down into glucose (and eventually glycolysis) through catabolism. Proteins are broken down by protein degradation and lipids through lipolysis. Nucleic acids are first broken down into smaller fragments, but then must be broken down even further before absorption can occur. Brush border enzymes are attached to the exposed surfaces of microvilli in the last enzymatic steps. Then nucleic acids are of 368 The Gallbladder The gallbladder is a hollow, pear-shaped organ that stores and concentrates bile before its excretion into the small intestine. This muscular sac is located in a fossa, or recess, in the posterior surface of the liver’s right. The gallbladder split into three regions: the fundus, the body, and the neck. The cystic duct extends from the gallbladder to the point where its union with the common hepatic duct forms the common bile duct. At the duodenum, the bile duct meets the pancreatic duct before emptying into a chamber called the duodenal ampulla . The duodenal ampulla opens into the duodenum at the duodenal papilla , a small mound. The muscular hepatopancreatic sphincter ( sphincter of Oddi ) surrounds the inside cylindrical space (known as a lumen) of the common bile duct, pancreatic duct, and duodenal ampulla as well. The Pancreas The pancreas lies posterior to the stomach, extending laterally from the duodenum toward the spleen. The broad head of the pancreas lies within the loop formed by the duodenum as it leaves the pylorus. The slender body of the pancreas extends toward the spleen, and the tail is short and bluntly rounded. The pancreas is primarily an exocrine organ, producing digestive enzymes and buffers. The large pancreatic duct ( duct of Wirsung ) delivers these secretions to the duodenum. The pancreatic duct extends within the attached mesentery to reach the duodenum, where it meets the common bile duct from the liver and gallbladder. The two ducts then empty into the duodenal ampulla ( ampulla of Vater ), a chamber located roughly halfway along the length of the duodenum. 23.13 Digestion A typical meal contains carbohydrates, proteins, lipids, water, electrolytes (minerals), and vitamins. The digestive system handles each nutrient differently. Digestion will break down larger organic molecules first before absorbing them into the body. While water, electrolytes, and vitamins can be absorbed without preliminary processing. The Processing and Absorption of Nutrients