Exocrine Pancreas, Liver and Gallbladder

Study Notes

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

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

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 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 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