Anatomy & Physiology I and II

Anatomy & Physiology Study Guide , 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 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 themdown 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 broken down further into nucleotides. Next, brush border enzymes digest these nucleotides into sugars, phosphates, and nitrogenous bases that are absorbed by active transport. However, nucleic acids represent only a small fraction of all the nutrients absorbed each day. Once the molecules are broken down into their purest form, the body uses these substances for energy through a series of chemical reactions that form a metabolic process called the Kreb , or TCA , cycle. This process is aerobic, which means it requires oxygen, and when energy is created, it is temporarily held by the ©2018 Achieve Test Prep Page 322 of 367 a chamber called the duodenal ampulla duodenal papilla . The duodenal ampulla opens into the duodenum at the