Tues Anatomoy ?'s

Tuesday Ju 13 Homework
1. Describe the 4 “true” hormones in the GI tract and what they do.
The four "true" hormones are gastrin, secretin, CCK, and GIP. Gastrin is secreted by cells in the stomach and it stimulates the parietal cells in the stomach to secrete HCL and intrinsic factor. Secretin is known as "nature's antacid". Secretin stimulates the pancreas to secrete carbonate ions so that the acidic stomach juices will be neutralized and not damage the small intestine. CCK is released from cells in the duodenum. CCK causes the gall bladder to release bile and the pancreas to release digestive enzymes. It also causes relaxation to the sphincter of Oddi so the pancreatic enzymes and bile can get to the duodenum more easily. GIP is released from cells in the duodenum. It increases motor activity and secretory activity of the stomach, but its primary job is to stimulate the pancreas to release insulin from the beta cells.
2. Describe the neuromuscular reflexes in the GI tract (how various organs communicate with each other).
The enterogastric reflex is stimulated when pH levels in the duodenum reach 3-4 or the stomach pH reaches 1.5. It inhibits the release of gastrin. This reduces gastric motility and secretion of HCl. The gastrocolic reflex is stimulated when the stomach stretches during a meal. It can increase motility and is responsible for the urge to defecate. The colonoileal reflex prevents the ilial contents from being emptied into the colon.