Bile Juice Bile is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver , it is stored in the gallbladder and upon eating is discharged into the duodenum. . The principal function of the gallbladder is to serve as a storage reservoir for bile. The main components of bile are water, bile salts, bile pigments, and cholesterol Bile salts act as emulsifying agents in the digestion and absorption of fats. Cholesterol and bile pigments from the breakdown of hemoglobin are excreted from the body in the bile. Physical properties; Hepatic bile: pH 7.4, colour is golden yellow , Bladder bile: pH 6.8, color is green dark to yellow (darker) Volume of bile produced reaches to one liter of bile per day (depending on body size).
Bile Juice Bile Composition; Water (85%), bile salts (10%),(Cholic, chenodeoxycholic, deoxycholic, and lithocholic acid) mucus pigments (3%), bile pigments e.g bilirubin glucuronide fats (1%), such as Phospholipids (lecithin) , cholesterol. 0.7% inorganic salts.
Bile secretion Bile is secreted in two stages ; Stage one; the liver hepatocytes will secret an initial secretion that is rich in bile salts , cholesterol, and other organic components, the initial secretion will drain through the many minute bile canaliculi that penetrate the liver. Stage Two ; The initial secretion will flow towards the bile ducts , during its flow in the ducts a secondary secretion is added to the initial bile which is a watery solution of sodium bicarbonate ions. The bile then will either empty into the duodenum when the sphincter of Oddi is open, Or( when the sphincter of Oddi is closed) it will be prevented from draining into the intestine and instead flows into the gallbladder, where it is stored and concentrated to up to five times its original potency . This concentration occurs through the absorption of water sodium , chloride and other electrolytes, while retaining and concentrating all the original organic molecules.
Bile secretion
Bile secretion stimulation 1-Under neural control mediated by e.g acetyl choline. 2- Under hormonal control ; When food is released by the stomach into the duodenum in the form of chyme, the duodenum releases cholecystokinin, which is the main stimulant causing the gallbladder to release the concentrated bile to complete digestion. - Gastrin and secretin also stimulate bile secretion. Lack of bile salts in the enterohepatic circulation stimulates bile synthesis and secretion.
Enterohepatic Circulation About 95% of the salts secreted in bile are reabsorbed actively in the terminal ileum and re-used. Blood from the ileum flows directly to the hepatic portal vein and returns to the liver where the hepatocytes reabsorb the salts and return them to the bile ducts to be re-used, sometimes two to three times with each meal.
Function of bile juice 1- It is important in the digestion and absorption of lipids; Bile acts as a surfactant , helping to emulsify the fats in the food. Bile salt anions have a hydrophilic side and a hydrophobic side, and therefore tend to aggregate around droplets of fat ( triglycerides and phosphiolipids ) to form micelles, with the hydrophobic sides towards the fat and hydrophilic towards the outside. The hydrophilic sides are positively charged due to the lecithin and other phospholipids that compose bile, and this charge prevents fat droplets coated with bile from re-aggregating into larger fat particles. The dispersion of food fat into micelles thus provide a largely increased surface area for the action of the enzyme pancreatic lipase thus aiding in the digestion of lipids.,
Function of bile juice 2- Bile serves as the route of excretion for bilirubin. 3-The alkaline bile has the function of neutralizing any excess stomach acid before it enters the ileum. 4-. Bile salts also act as bactericides, destroying many of the microbes that may be present in the food.
Abnormalities associated with bile Gall stone ; The majority of gall stones are made up of cholesterol , (cholesterol tends to accrete into lumps in the gallbladder) Causes of gall stones; - Too much absorbtion of water from the bile . - Too much cholesterol in bile. - Inflammation of the epithelium.
Secretion of the small intestine * Intestinal glands Brunner’s gland (basic mucus) Lieberkuhn Crypt (main part) * Nature, Compositions & functions pH 7.6, iso-osmotic solution, 1~3 L/day Enterokinase, the only one secreted Oligopeptidase, oligosaccharidase those contained in the epithelial cells * Regulation of secretion of small intestine Mainly through plexus reflex initiated by inflation of the intestine
* Control of bile secretion & gallbladder emptying Nervous regulation Vagus nerve: ACh, gastrin Hepatic bile secretion (small amounts) Gallbladder contraction (slightly) Humoral reulation Gastrin: direct to hepatic cells & gallbladder; indirect to stomachHClsecretin Secretin: act to bile duct & not to hepatic cells, so: H2O & HCO3, bile salt () Cholecystokinin (CCK): gallbladder contraction & Oddi’s sphincter dialation Bile salt: enterohepatic circulation of bile salt
Bile secretion & gallbladder emptying * Nature, Compositions & functions Hepatic bile: pH 7.4, golden yellow Bladder bile: pH 6.8, color become darker Compositions: H2O, ions, bile acid, bile pigment, fatty acid, cholesterol, lecithin, mucoprotein, etc., but no enzyme Functions of bile (mainly by bile salt): Fat emulsification; lipid absorption; Promote the absorption of fat-soluble Vits
§ 4. Digestion in the intestine Pancreatic juice & its secretion * Nature, Compositions & functions pH 7.8~8.4, colorless & odourless, 1~2 L/day Bicarbonate (HCO3) Neutralize HCl & provide a weak basic medium favoring digestive enzyme action Pancreatic enzymes: amylase, lipase, colipase, trypsinogen & chymtrypsinogen, etc. Turn trypsinogen into trypsin by entero- kinase, turn chymtrypsinogen into chym- trypsin by trypsin Trypsin inhibitor: a polypeptide