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Regulation of Pancreatic and Bile Secretion

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Regulation of Pancreatic and Bile Secretion REGULATION OF PANCREATIC NERVE SUPPLY OF THE PANCREAS AND BILE SECRETION Like the stomach, the pancreas receives both: OBJECTIVES 1. Parasympathetic nerve fibers from the vagus Pancreatic juice 2. Sympathetic nerve fibers from the greater Biliary system splanchnic nerve Liver bile Functions of gall bladder THE PANCREATIC JUICE THE PANCREAS - The most important digestive juice The pancreas is both an endocrine and exocrine - 1.5 liters/day gland. - Alkaline in reaction (pH is about 8) because it has a ENDOCRINE PARTS EXOCRINE PART high bicarbonate content islets of Langerhans compound alveolar gland secretes hormones secretes the pancreatic Composition of the pancreatic juice juice The pancreatic juice is formed of 2 main parts: The pancreatic secretion is conducted to the AN AQUEOUS PART AN ENZYMATIC PART duodenum through a system of ducts. The small watery juice rich in viscid juice ducts drain into a single large duct which bicarbonate usually joins the common bile duct forming the secreted by the duct cells secreted by the ampulla of Vater. pancreatic alveoli This opens through the duodenal papilla and its opening is encircled by the sphincter of Oddi. Function of bicarbonate solution The bicarbonate solution in aquous secretion Neutralized the acid chyme Protects the delicate duodenal mucosa from excess acidity Washes out the thick viscid enzymatic part secreted by the alveoli Thug’s The pancreatic enzymes Control of pancreatic secretion 1. PROTEOLYTIC ENZYMES 3. LIPOLYTIC ENZYMES The secretion of the pancreatic juice is Trypsinogen Pancreatic lipase controlled by both: Chymotrypsinogen Phospholipase A 1. nervous mechanism Proelastase Pancreatic esterase 2. hormonal mechanism (more Procarboxypeptidase important) 2. PANCREATIC ALPHA-AMYLASE 4. PANCREATIC NUCLEASES NERVOUS CONTROL PARASYMPATHETIC SYMPATHETIC Stimulation of the vagus nerve. Decreases the pancreatic secretion particularly Causes secretion of pancreatic juice little in bicarbonates. amount but rich in enzymes. Nicotine stimulates the sympathetic fibers and inhibits the Occurs by the conditioned & unconditioned release of secretin hormone. reflexes Both effects reduce bicarbonate secretion from the During the cephalic phase pancreas and favors duodenal ulcers in cigarette smokers. HORMONAL CONTROL Two gastrointestinal hormones affect pancreatic secretion: SECRETIN CHOLECYSTOKININ (CCK) secreted by the duodenal mucosa secreted by the duodenal mucosa on contact with the acid chyme on contact with the digestive products of proteins and fats. delivered from the stomach stimulates the secretion of the enzymatic part of the pancreatic juice . Physiological effects of secretin hormone 1. Stimulates the secretion of the aqueous part of the pancreatic juice. 2. Inhibits the secretion of gastric HCl. 3. Inhibits the gastrointestinal motility. 4. Stimulates the secretion of watery bile rich in inorganic constituents Thug’s LIVER BILE CONTROL OF GALLBLADDER EVACUATION NERVOUS CONTROL HORMONAL CONTROL COMPOSITION OF LIVER BILE Stimulation of the The hormone CCK The liver bile is a golden yellow alkaline fluid vagus Causes contraction (pH 7.8-8.6) Causes relaxation of of the gallblader 500-800 ml/day sphincter of Oddi & wall & evacuation Composed of weak contraction of of its contents into 1. Water the gallbladder. the duodenum. 2. Inorganic constituents: Na, HCO3, Cl Is stimulated by meals 3. organic constituents: Bile salts, bile through conditioned pigments, lipids and unconditioned reflexes During cephalic phase REGULATION OF BILE SECRETION AND FLOW of gastric secretion (factors affecting bile secretion) 1. Hepatic blood flow 2. Vagal stimulation CHOLERETICS CHOLAGOGUES 3. Bile salts --it is choleretic substances that substances that cause 4. The hormone secretin (hydrocholeretic effect) increase bile secretion contraction of the gallbladder by the liver. thus increasing the bile flow into the duodenum. PHYSIOLOGIC FUNCTIONS OF THE GALLBLADDER Bile salts & secretin CCK . 1-Storage of bile hormone. 2-Concentration of bile 3-Acidification of bile DRUGS 4-Secretion of mucus Vasodilator drugs that magnesium sulphate and 5-Evacuation increrase the hepatic cholinergic drugs which cause weak contraction of the 6-Decreasing the pressure in the bile ducts secretion. gallbladder. Thug’s FUNCTIONS OF BILE BILE PIGMENTS 1. contains bile salts that are essential for fat The bile pigments are the end-products of digestion and absorption & other important hemoblobin metabolism. functions. The remaining part of the haem molecule (after 2. The alkali content of bile helps neutralization of removing the iron) is converted into a yellow gastric HCl. pigment called bilirubin. 3. The mucin in bile acts as lubricant in the small This occurs in the RES cells. intestine. Bilirubin is secreted by the liver cells into the 4. An excretory route for many substances as bile bile as bile pigments. pigment and drugs. Effects of common bile duct obstruction 1. Obstructive jaundice 2. Impaired liver functions BILE SALTS 3. Decreased flow of bile salts into the intestine These are Na+ and K+ salts of bile acids 4. Pruritis (itching) conjugated to glycine and taurine. 5. Bradycardia The Enterohepatic circulation of the bile salts: 90-95% of bile salts are actively reabsorbed from the terminal ileum and returns to the liver where they are resecreted. Functions of the bile salts 1. Help digestion of fat by Emulsification(decrease surface tension) Dissolve FA Activate pancreatic lipase enzyme 2. Help absorption of fat & fat soluble vit 3. Solvent action, keep cholesterol dissolved in bile. 4. Laxative effect 5. Choleretic effect 6. Anti putrifaction action 7. Help absorption of Ca,Mg,Fe Thug’s .
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