Physiology Anatomy of Gastrointestinal System , Lecture Notes Part2 البروفسیور د. علي التمیمي

Physiology & Anatomy of Gastrointestinal System , Lecture Notes Part2 

البروفسيور د. علي التميمي ,استاذ الباثوفسيولوجي والتشريح المرضي,دكتوراة الكلية الملكية انكلترا

,وزميل كلية الامراض  البورد الامريكي

Prof Ali Altimimi Professor of PathoPhysiology & Anatomical Pathology

MbCHB,MSC,PHD,MD.Royal College London

محاضرات للاقسام الطبية لطلبة كلية الرافدين الجامعة

Small Intestine
The small intestine extends from the pylorus to the ileocecal valve. The small intestine is composed of the duodenum ,jejunum, and ileum. The ligament of Treitz divides the duodenum from the jejunum. Upper gastrointestinal bleeding occurs above this ligament and lower gastrointestinal bleeding occurs below this ligament.  
The primary function of the small intestine is the absorption of vitamins and nutrients, including electrolytes, iron, 
carbohydrates, proteins, and fats. Most digestion of nutrients happens here.

Three thousand milliliters of digestive enzymes are secreted in the small intestine daily.   These enzymes include:   Lipase – splits fats into monoglycerides, glycerol, and fatty acids  Amylase – converts starch to maltose  Maltase – converts maltose to glucose  Lactase – converts lactose into galactose and glucose  Sucrase – converts sucrose into fructose and glucose  Dextrinase   converts specific dextrins into glucose  Intestinal Hormones  The mucosa in the intestines also contains hormones. These include:  Enterogastrone: Found in the duodenal mucosa. Inhibits gastric acid secretion and gastric motility.  Gastric inhibitory polypeptide (GIP): Found in the duodenal and jejunal mucosa. Inhibits gastric acid secretion, pepsin  secretion, and gastric motility.  Secretin: Found in the duodenal mucosa. Stimulates pepsinogen secretion, secretions of pancreatic digestive enzymes,  and secretion of bile from the liver. Also decreases gastric acid secretion. 

Cholecystokinin (CCK): Found in the jejunal mucosa. Stimulates contraction of the gallbladder and secretion of  pancreatic enzymes, and inhibits gastric motility.  Vasoactive intestinal peptide (VIP): Found in intestinal mucosa. Similar effects as secretin, stimulates production of  intestinal secretions that decrease chyme acidity, and inhibits gastric secretion.  Somatostatin: Found in the intestines. Inhibits secretion of gastric acid, saliva, pepsin, intrinsic factor, and pancreatic  enzymes. Inhibits gastric motility, gallbladder contraction, intestinal motility, and blood flow to the liver and intestine.  Also inhibits secretion of insulin and growth hormone.  Serotonin: Found in the intestines. Inhibits gastric acid secretion. 

Intestinal Blood Supply & Innervation   Blood supply to the small intestine is derived from: 

 The celiac artery   The superior mesenteric artery

Innervation of the small intestine is the same as for the stomach . Peristalsis is the process of wave‐like muscular contractions that move digested material through the intestine. The  process of digestion is completed in the small intestine. At this stage the nutrients that the body needs are absorbed through the walls of the small intestine.  Peristalsis occurs via the autonomic nervous system and is coordinated by the  myenteric plexi. Peristaltic activity is generally weak, but can be increased by laxatives and certain kinds of illness or  toxicity .  

The large intestine extends from the terminal ileum at the ileocecal valve to the rectum. At the terminal ileum, the large intestine becomes the ascending colon, the transverse colon, and then the descending colon. Following the descending  colon is the sigmoid colon an

d the rectum . 
The main function of the large intestine is water absorption. Typically, the large intestine absorbs about one and one‐half liters of water per day. It can, however, absorb up to six liters.   The large intestine also absorbs potassium, sodium, and chloride. It produces mucous which lubricates the intestinal   wall and holds the produced feces together for elimination.