Published on September 3, 2012
Gallbladder & Bile : Gallbladder & Bile Dr Raghuveer Choudhary Saturday, April 21, 2012 PowerPoint Presentation: When no chyme is in the small intestine, the hepatopancreatic sphincter is closed. Bile flows into gallbladder. cystic duct common hepatic duct gallbladder common bile duct hepatopancreatic sphincter pancreas duodenum PowerPoint Presentation: Function of Gallbladder - absorbs water and stores the bile for later use. gallbladder hepatopancreatic sphincter duodenum Liver and Gall Bladder: 5 Liver and Gall Bladder The liver has many functions, one of which is to produce bile to aid in the digestive process. Bile acts to help neutralize the chyme as it enters the small intestine and is a fat emulsifier. It breaks up fats into tiny particles so that they are more accessible to digestive enzymes. The gallbladder is chiefly a storage organ for bile. Gallbladder & Bile : Gallbladder & Bile Sac on underside of liver Stores and concentrates bile Bile – yellow – green fluid Contains minerals, cholesterol, neutral fats, phospholipids, bile pigments, bile acids (salts) Bile salts aid in digestion of fats Excessively concentrated = gallstones 80% bile salts recycled 20% bile – excreted in feces Gallbladder: Sac-like organ attached to the inferior surface of the liver. Stores and concentrates bile. When gallbladder fills with bile, it expands. Contraction of the muscularis layer of the gallbladder, ejects bile into the common bile duct into duodenum. When small intestine is empty, sphincter of Oddi closes. Bile is forced up to the cystic duct to gallbladder. Gallbladder The Gallbladder and Bile Modification: The Gallbladder and Bile Modification Full gallbladder contains 40–70 ml bile Bile composition gradually changes in gallbladder: water is absorbed bile salts and solutes become concentrated Regulation of bile release: 10 Regulation of bile release The liver makes bile continuously. When there is no food in the small intestine, the hepatopancreatic sphincter (the entrance of the common bile duct and pancreatic duct into the small intestine) is closed and the bile backs up into the gallbladder. Regulation of bile release: 11 Regulation of bile release When food enters the small intestine, activation of mechano and chemoreceptors leads to parasympathetic stimulation. This mildly stimulates gallbladder contraction This also stimulates the release of cholecystokinin and secretin from the duodenal and enteroendocrine cells. Bile Release: Bile Release PowerPoint Presentation: - is constantly produced by the liver (500-1,000 mL of bile per day). - is a yellow-green fluid containing : minerals bile pigments bile acids phospholipids cholesterol neutral fats Bile facilitate fat digestion and absorption Composition of bile: 16 Composition of bile Bile is an alkaline solution containing a number of components. The important ones for digestion are bile salts, cholesterol and phospholipids. Bile salts act as a fat emulsifier – they break globules of fat entering the small intestine into millions of fatty droplets. This provides a large surface area for the fat digesting enzymes to work on. PowerPoint Presentation: 17 Composition of Bile Bile Production and Secretion (continued): Bile Production and Secretion (continued) Bile acids are derivatives of cholesterol. Major pathway of cholesterol breakdown in the body. Principal bile acids are: Cholic acid. Chenodeoxycholic acid. Combine with glycine or taurine to form bile salts. Bile salts aggregate as micelles. 95% of bile acids are absorbed by ileum. Insert fig. 18.25 PowerPoint Presentation: Biliary Secretion Bile is secreted continuously by the liver, and the rate of secretion depends on whether a fed or fasting state exists. B. Bile contains bile salts, lecithin (a phospholipid ), cholesterol, bile pigments ( eg , bilirubin ), water, and electrolytes. C. Bile constituents are dissolved in an alkaline solution resembling pancreatic juice. Bile plays an important role in the intestinal digestion and absorption of lipids. D. Primary bile acids— cholic acid and chenodeoxycholic acid—are synthesized by the liver from cholesterol. The lipid-soluble bile acids are conjugated with either glycine or taurine . PowerPoint Presentation: Because they are ionized at neutral pH, conjugated bile acids exist as salts of sodium or potassium and, therefore, are known as bile salts. F. Secondary bile acids are formed by deconjugation and dehydroxylation of the primary bile salts by intestinal bacteria, forming deoxycholic acid from cholic acid and lithocholic acid from chenodeoxycholic acid. G. Lithocholic acid is hepatotoxic and is normally excreted in feces. H. The bile acid pool, which under normal conditions is constant in size (about 2–4 g), is a mass of primary and secondary bile acids. PowerPoint Presentation: Fats are first broken up into smaller emulsification droplets by lecithin and bile salts (acids) in the bile. PowerPoint Presentation: 2) When lipase digests fats, the products are two fatty acids (FFAs) and a monoglyceride . PowerPoint Presentation: 3) Bile salts coat these and other lipids and form droplets called micelles . PowerPoint Presentation: Micelles release their lipids, which diffuse freely across the plasma membrane. PowerPoint Presentation: Resynthesis of triglycerides . Coating with protein, forming droplets called chylomicrons . Intestinal absorptive cell PowerPoint Presentation: Chylomicrons are too large to enter blood capillaries and must be first transported in the lymphatic lacteal . PowerPoint Presentation: Fat globule emulsification droplets micelles chylomicrons Intestinal lumen Intestinal epithelial cells lacteal blood Bile salts lipase & bile salts PowerPoint Presentation: Effects of Cholecystectomy The periodic discharge of bile from the gallbladder aids digestion but is not essential for it. Cholecystectomized patients maintain good health and nutrition with a constant slow discharge of bile into the duodenum, although eventually the bile duct becomes somewhat dilated, and more bile tends to enter the duodenum after meals than at other times. Cholecystectomized patients can even tolerate fried foods, although they generally must avoid foods that are particularly high in fat content.