Exocrine Pancreas, Liver and Gallbladder

Exocrine Pancreas, Liver and Gallbladder

• The pancreas is a mixture of exocrine and endocrine tissue
• The endocrine pancreas (islets of Langerhans 1%) secretes hormones like glucagon, insulin, somatostatin, and pancreatic polypeptide
• The exocrine pancreas (99%) secretes digestive enzymes and alkaline fluid into the small intestine
• Acinar cells secrete digestive enzymes
• Duct cells secrete aqueous NaHCO3 solution
• Pancreatic juice (1200-1500 ml daily) is mostly water, contains enzymes for all types of food, and sodium bicarbonate to neutralize stomach acid
• Pancreatic enzymes include trypsin, chymotrypsin, elastase, carboxypeptidase, lipase, amylase, ribonuclease, and deoxyribonuclease which act on proteins, proteins, proteins, fats, polysaccharides, and nucleic acids respectively

Pancreatic Juice Regulation

• Pancreas secretes inactive enzymes (zymogens) to prevent digestion of itself
• Trypsin inhibitor prevents activation of trypsin, and thus the activation of other pancreatic enzymes as well
• Secretin is released from the duodenum in response to stomach acid. It stimulates bicarbonate secretion by the pancreas
• Cholecystokinin (CCK) is released from the duodenum in response to fats and proteins. It stimulates enzyme secretion by the pancreas

Liver and Gallbladder Function

• The liver receives blood from the hepatic artery and hepatic portal vein
• The liver's blood supply is from the hepatic artery, carrying oxygenated blood; the hepatic portal vein, carrying nutrient rich blood from the digestive organs.
• Hepatic vein carries venous blood from the liver
• Hepatocytes are major cells in the liver, playing a vital role in chemical processes
• Hepatic sinusoids are leaky capillaries facilitating exchange
• Kupffer cells are fixed macrophages within the liver
• Branches of the hepatic portal vein, hepatic artery, and bile duct form the hepatic triad
• Bile is secreted continuously from the liver via hepatocytes at a rate of 500-1000ml per day
• Bile is stored and concentrated in the gallbladder until released in response to a meal
• Composition includes bile acids (synthesized from cholesterol), water, cholesterol, lecithin, bile pigments (bilirubin), and inorganic ions (HCO3- and Cl-)
• Bile salts emulsify fats, increasing surface area for lipase digestion and absorption

Bile Salt Functions

• Bile salts enhance absorption of fatty acids and cholesterol by forming micelles in chyme
• Micelles are small spherical structures that transport lipids in the intestinal lumen
• Bile salts are recycled via the enterohepatic circulation

Gallbladder Function

• Gallbladder stores and concentrates bile between meals
• Sphincter of Oddi controls bile release into duodenum; it's closed between meals
• In digestion, the sphincter of Oddi opens allowing bile to enter the duodenum to aid in fat digestion/absorption
• Cholecystokinin (CCK) stimulates gallbladder contraction and relaxation of the sphincter of Oddi for efficient bile release into the intestine