NS 3310 1st EditionExam # 1 Study Guide Chapters 1-3Ch. 1How is glucose regulated by insulin?Insulin secretion after a meal is initiated by a rise in extracellular glucose, which is detected by a metabolic signaling pathway. Aerobic glycolysis and mitochondrial oxidation produce metabolic signals, such as a rise in the ATP to ADP concentration ratio. This closes potassium channels, depolarizes the plasma membrane and causes calcium influx that stimulates exocytosis. At the same time, the incretin hormones GLP1 and GIP bind to their receptors, which are highly expressed on beta cells. This causes the activation of G proteins. The glucose and GLP1 signalingpathways converge on AC8. The subsequent rise in cellular cAMP triggers exocytosis by protein kinase A and EPAC2. What are the three ways that cells can receive signals?1) Signal through cell surface receptor: G-protein coupled receptor; Ligand activates receptor and receptor can either directly signal downstream through a mechanism that involves phosphorylation or go through G proteins that activate adenylate cyclase which produces cAMP.2) Through a channel: extracellular signal can directly into the cell. This is for charged ions. 3) Extracellular signal directly comes into the cell and binds to receptors inside the cell. Binding of these receptors can activate gene transcription in the nucleus.Ch. 2What composes each of the layers of the digestive tract and what is each layer’s function?There are four layers. The innermost layer is the mucosa, which is composed of epithelium, lamina propria and muscularis externa. Its function is to produce and release secretions needed for digestion. Next to the mucosa is the submucosa, which is composed of connective tissue, lymphoid tissue and submucosal plexus. Its function is to protect the body from bacteria. Then is the muscularis externa, which is composed of circular and longitudinal smooth muscle. This layer is responsible for GI motility. The outer layer is the serosa, which is composed of connective tissue that protects the GI tract. What do each of the cells of the gastric pit produce?Neck cells secrete bicarbonate and mucus that forms the gastric mucosal barrier-protecting the mucosal lining from low pH. The chief cells produce enzymes needed for protein digestion(pepsinogen). The parietal cells secrete HCl and intrinsic factor and the enteroendocrine G-cells produce the hormone gastrin, which stimulates parietal and chief cells. Thus, the gastric juice is composed of mucus, enzymes, intrinsic factor and HCl.What is the function of the Sphincter of Oddi?The duodenum receives secretions from the gallbladder via the common bile duct. The pancreas releases its sections from the pancreatic duct, which eventually joins the common bile duct. The sphincter of Oddi regulates the flow of these secretions into the duodenum. How does the intestinal bacteria benefit the host?It provides host defense. It protects the body from foreign bacteria. It provides immune development and nutrition. Describe bile synthesis in the liver.Bile is produced and secreted by hepatocytes into a special duct called a bile canaliculus. Bile is synthesis consists of: the formation of cholic and chenodeoxycholic acid from cholesterol. The rate-limiting enzyme, CYP7A1 converts cholesterol to bile acid. The bile acids are then conjugated with glycine and taurine. Bile is then concentrated, stored and secreted by the gallbladder. The bile constituents are: bile acids/salts, cholesterol, phospholipids and bile pigments. Bile’s function is to act as detergents to emulsify lipids and form small spherical complexes called micelles.What is enterohepatic circulation of bile?Enterohepatic circulation is the process of reusing bile. First, bile is made in the liver and transported to the gallbladder where it is stored. When the gallbladder contracts, bile is released into the cystic duct. The cystic duct joins the common bile duct. Bile aids in lipid digestion by enabling large lipid globules to disperse in the watery environment of the small intestine. After aiding in lipid digestion, the bile constituents are reabsorbed from the ileum andreturned to the liver via the hepatic portal vein. The liver uses these constituents to resynthesize bile, which is then stored in the gallbladder. What does trypsinogen do?Trypsinogen is activated by enteropeptidase to produce trypsin. Trypsin activates other proenzymes: chymotrypsiongen, procarboxypeptidase, procolipase and prophospholipase to produce their active form. Describe Cholesterol Gallstone Disease (CGD).CGD is characterized by cholesterol precipitation in bile, increased bile salt hydrophobicity and gallbladder inflammation. The key transcription factor is FXR, which is a protein that binds to DNA sequence and activates or represses gene transcription. FXR binds to specific DNA response elements as a heterodimeric complex with the retinoid X receptor. High concentration of bile activates this complex in hepatocytes. FXR goes to the nucleus and activates gene transcription of transporters while repressing CYP7A1. This reduces bile acid pools by reducing synthesis and increasing export. If there is a low bile acid condition in hepatocytes, FXR won’t beactivated because there is not enough hormone to activate it. CYP7A1 will be activated so there will be more bile acid synthesis and export of bile acid will be reduced so there will be more bileacid in the cell. Ch. 3Describe carbohydrate digestion.Polysaccharide digestion begins in the mouth with salivary alpha amylase. It then goes into the small intestine, where it is digested by pancreatic alpha amylase. They are now disaccharides which are digested in microvilli of enterocytes by disaccharidases. What is the difference between glucose/galactose absorption from that of fructose?Glucose and galactose are absorbed into the cell by activate transport via SGLT1. They are then absorbed into the blood by facilitated diffusion using GLUT2. The absorption of fructose into thecell is primarily by GLUT5 via facilitated diffusion. Then, it is absorbed into the blood by facilitated diffusion GLUT2. What is insulin’s role in cellular glucose absorption and metabolism?Insulin is a very powerful anabolic hormone. It binds to the membrane insulin receptor and stimulates GLUT4 exocytosis to move to the membrane in adipocytes and myocytes. It promotesglucose phosphorylation and anabolism. Insulin reacts with a membrane receptor that