1-It is to prevent back flow of fecal content from colon into small intestine.

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1 Function of the ileocecal valve: 1-It is to prevent back flow of fecal content from colon into small intestine. 2-The wall of the ileum for several centimeters preceding valve has a thickened muscular coat called ileocecal sphincter. which is normally remain constricted. 3-Gastrin which is liberated from the stomach mucous in response to food in the stomach has relaxant effect on the ileocecal sphincter, following meal, 4-gastroileal reflex occur, both of them cause an increase emptying. When cecum is distended.. 5-the degree of contraction of ileoccal sphincter, ileac peristalsis inhibited which greatly delays emptying of additional chyme from the ileum. 6- Any irritant in the cecum delays emptying. These reflexes from the cecum to the ileocecal sphincter and ileum are mediated both by enteric nervous system and through vagovagal reflexes. Structure of pancreatic exocrine glands: The exocrine pancreas comprises 90% of pancreas acini, which is the blind end of a branching duct system is lined with aciner cells, that secrete the enzymatic portion of pancreatic secretion. The ducts are lined with ductal cells, ductal epithelial cells extend into the acinus' into a special region of centroacinar cells. Secrete aqueoushc0 3. Figure (9).

2 Pancreatic secretion: The exocrine part of pancreas secretes I litter I day of fluid into the lumen of the duodenum. The secretion consists of an aqueous component high in HCO3 to neutralize the H + from stomach and an enzymatic component to digest carbohydrates, proteins and lipid. aqueous secretion rich in bicarbonate,na+, K-, CL -,its responsible for washing out the acini and duct to pare enzymes secretion into the duodenum and also the responsibility for neutralization of the intestinal content by bicarbonate to shi the ph to 6-7 which is essenal for enzyme activity. While the endocrine part which secrete insulin and glucagon,endocrine cells present as islets of langerhans αandβ cells.

3 Acini cell centroaciner Ductal cell Figure (9) pancreatic secretion Exocrine pancreas is innervated by both parasympathetic and sympathetic nervous system, Parasympathetic activity stimulates pancreatic secretion, and sympathetic activity inhibits pancreatic secretion ( in contrast with the salivary gland, in which both sympathetic and parasympathetic activity are stimulatory). The pancreatic secretion are: 1- The proteolytic enzymes for proteins digestion; are trypsin. chymotrypsin. The intestinal mucous secret Amino-oligopeptiase and Dipeptidase. 2- The digestive enzyme for carbohydrates is pancreatic amylase which hydrolyzes starches, glycogen. The intestinal mucous secret sucrase, maltase, lactase.

4 3- The main enzyme for fat digestion is pancreatic lipase which is capable of hydrolyzing neutral fat into fatty acids Pancreas protects itself from auto digestion:- by proteolytic enzymes by the following ways: A- When synthesized in the pancreatic cells, they are in the inactive forms, These become activated only after they are secreted into the intestinal tract, they are activated by an enzymes are secreted by the intestinal mucous. B- The same cells that secrete the proteolytic enzymes into the acini of the pancreas secrete another substance called trypsin inhibitor. This substance is stored in the cytoplasm of the glandular cells surrounding the enzyme granules and it prevents activation of trypsin both inside the secretary cells and in the acini and ducts of the pancreas. Regulation of pancreatic secretion: Pancreatic secretion is regulated by both nervous and hormonal mechanisms. Hormonal regulation is more important. Like gastric, pancreatic secretion is divided into the following three phases: 1- Cephalic phase: The thought, smell, and taste of food produces the cephalic phase of pancreatic secretion. Both acinar and to less extent the ductal cell secretion are enhanced by vagal stimulation. Most the enzymes are stored in the acini. 2- Gastric phase: Pancreatic secretion is enhanced during the gastric phase by : A- Distention of the antrum and the body of the stomach which initiates avagovagal reflex resulting in a low volume of pancreatic secretion containing both bicarbonate ions and enzymes. B- Food breakdown products (amino acid and peptides) stimulate pancreatic secretion by release gastrin ( from G cells of antrum) which produces a low-volume, high enzyme pancreatic secretion.

5 3 - Intestinal phase: The most important for pancreatic secretion are hormone CCK( and secretin. They are released from endocrine cells in the duodenum and jejunum during the intestinal phase in response to the entrance of chyme into the small intestine. The amino acids, fatty acids are the major stimuli for (CCK) secretion from I cells which found in upper small intestine. CCK( in addition to its effect on the gallbladder, is a potent stimulant of pancreatic enzyme secretion,by its effect on the acinar cells which trigger the second messenger inisitol tri phosphate(ip3) and then cells makes the enzymes. Secretin present in S cells that found in upper small intestine this cells triggers camp in the ductal cells to smu l at es the HCO3 secreon. Low ph( <4. 5) due to pr es ence of gastri c aci d in the int es ne, stimulate for the release of secretin. This causes large quantities of pancreac jui ce cont ai ni ng HCO3. Fi gur e( 10)