LIVER physiological Anatomy: liver is the largest organ of the body, located in the upper right and central portions of the abdominal cavity ,just below the diaphragm.
Functions of the liver
1.Formation and secretion of bile.2.Metabolic functions :a. carbohydrate metabolismb. Protein metabolism c. fat metabolism3. Vascular function for storage and filtration of blood.4.Immunity functions: presences of kupffer’s cells5. Other metabolic functionsBile
physiological anatomy of biliary secretion The intrahepatic bile duct form the right and left hepatic ducts which join to form common hepatic duct. The cystic duct drains the gall bladder. The common hepatic duct unites the cystic duct to form the common bile duct , enter the duodenum at the duodenal papilla, its orifice is surrounded by the sphincter of Oddi and unite with the main pancreatic duct just before entering the duodenum.normally between 600 and 1000 ml/day. Bile serves two important functions: 1. bile plays an important role in fat digestion and absorption, not because of any enzymes in the bile that cause fat digestion, but because bile acids in the bile do two things: a. they help to emulsify the large fat particles of the food into many minute particles, the surface of which can then be attacked by lipase enzymes secreted in pancreatic juice b. they aid in absorption of the digested fat end products through the intestinal mucosal membrane .
2. bile serves as a means for excretion of several important waste products from the blood. These include especially bilirubin, an end product of hemoglobin destruction, and excesses of cholesterol
Secretion of Bile: there are two stages for its secretion: 1. The initial portion is secreted by the liver hepatocytes; contain large quantities of Bile acids, Cholesterol and other organic constituents into minute bile canaliculi between the hepatic cells. the bile flows in the canaliculi toward the interlobular septa, where the canaliculi empty into terminal bile ducts and then into progressively larger ducts, finally reaching the hepatic duct and common bile duct. From these the bile either empties directlyinto the duodenum or is diverted for minutes up toseveral hours through the cystic duct into the gallbladder,
2. A second portion is a solution of NaHCO3 added to the initial constituents secreted by the secretory epithelial cells of ductules and ducts. This increases the total amount of bile as much as 100% it is stimulated by secretin.
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Composition of Bile
GALL BLADDER
functions of gallbladder: 1.Storage of bile: The bile secreted by the liver cells is normally stored in the gall bladder until needed. The maximum volume of gallbladder is 30-60 ml. Within 24 hours 450ml of bile is secreted, but H2O, Na+, Cl- and other small electrolytes are absorbed by the mucosa of the gall bladder concentrating other constituents by 5 folds, sometimes up to 20 folds. 2.Acidification of bile pH of bile in liver is 7.8-8.6 wherase PH in gallbladder is 7-7.4Gall Bladder Emptying 1. Role of cholecystokinin( cck) 2. Role Acetylcholine: Vagal stimulation causes weak contraction of gall bladder
Emptying of Gallbladder
Fatty food in the duodenum after 30 min after mealSecr. of CCK from duodenal mucosa I cells
Contraction of gallbladder and emptying of bile
Relaxation of the sphincter of Oddi
Secretion of enzymes from acinal cells of the pancreas (enzymes)
Blood
Secretin
Stimulate liver ductal secretion (NaHCO3)
Even with relatively strong contraction of the gall bladder, emptying is difficult because the sphincter of Oddi is tonically contracted.
1) Cholecystokinin contraction of G.B.
Relaxation of the sphincter of OddiEmptying of G.B.
2)Rhythmical contraction of the gallbladder peristaltic waves down the common bile duct Relaxation of oddi emptying of G.B.
3)Relaxation phase of the intestinal peristaltic waves relaxation of oddi most potent effect
Before emptying sphincter of Oddi must be relaxed, this occurs by the following factors:
Bile Salts Are sodium and potassium salt of bile acid conjugated to glycine or taurine ,derivative of cysteine Liver cells synthesize (6 gm) of bile salts daily the precursor is cholesterol which is either a) Synthesized by hepatocytes during the course of fat metabolism . Or b) Supplied in the diet Cholesterol converted to 1. Deoxycholic acid 2. cholic acid 3. cheno deoxycholic acid 4.lithocholie acid + glycine Or Taurine ----Glyco or tauro bile acids The salts of these acids, mainly sodium salts, are then secreted in the bile.
Functions of Bile salts 1) They have a detergent action on the fat particles in the food; by decreasing their surface tension. Allow agitation in the intestinal tract to break the fat globules into very small size (minute size). This process is called Emulsifying function or detergent function of bile salts. 2) It is more important than the first one. a. Bile salts helps in the absorption of Fatty acids, Monoglycerides, cholesterol and other lipids from intestinal tract.
b. They form complexes with these lipids, the complexes are called micelles. They are highly soluble; they are carried in this form to the mucosa where they are absorbed. (40% of the lipids are lost into the stools and a person develops a metabolic deficit due to nutrient loss if Bile salts are not present in the intestinal tract). Steatorrhorea. When fats are not absorbed deficiency of fat soluble vitamins A,D,E, and K developed. Deficiency of vit. K which results in deficiency in the formation of prothrombin and factors VII, IX and X serious impairment of blood coagulation.
4) Bile salts are totally absorbed when they pass through the venous sinusoids into the hepatic cells. 5) They are then resecreted into the bile. 6) By this way about 94% of bile salts are recirculated into the bile. 7) Bile slats make this entire circuit about 18 times before being carried out into the feces. The small amount 5-6% lost is replaced by new quantity formed continually by the liver cells.
The quantity of bile secreted by the liver depends on the availability of bile salts in the enterohepatic circulation≈ 2.5gm. Ingestion of excess of bile salts bile production and secretion by several 100ml/day. If a bile fistula empty the bile salt to the exterior so that they can not be reabsorbed from the ileum, the liver increases its production of bile salts 6-10folds. (The daily rate of bile salts secretion is actively controlled by the availability or lack of availability of Bile salts in the enterhepatic circulation).Secretin hormone act on epithelial cells of bile ductules and ducts secretion of HCO3 and watery solution.
RBC live 120 days Phagocytosis by macrophage Globin + Hb ----- heme Glonin ---- a.a iron and protoporphyrine---- heme Protoporphyrine ----- bilivirdin which chang to bilirubin Bilirubin free then trnasfered by albumin to the liver in the liver conjugated with gluc