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Biliary Secretions August 3, 2019 Biliary Secretion
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Functional Anatomy Hepatic artery Sinusoid Portal vein Central vein
Bile duct Bile canaliculi August 3, 2019 Biliary Secretion
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Functions Provide bile salts necessary
Digestion and absorption of fats Form important excretory pathway Water insoluble substances Cholesterol, steroid hormones, drugs, bilirubin August 3, 2019 Biliary Secretion
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Composition Bile is mixture of excretory and secretory products
Water, bile salts, bile pigments, inorganic salts, lipid materials Organic materials Bile acids, lethicin, cholesterol, Bilirubin, protein August 3, 2019 Biliary Secretion
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Composition Inorganic solutes Na+, K+, Ca++, Mg++, Cl-, HCO3-
August 3, 2019 Biliary Secretion
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Composition of Bile Hepatic bile Gall bladder bile Composition
Concentration Na+ meq/L 130 meq/L K+ meq/L 12 meq/L Ca++ meq/L 23 meq/L Mg++ meq/L HCO3- 17-56 meq/L 10 meq/L Cl- 100 meq/L 25meq/L August 3, 2019 Biliary Secretion
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Composition of Bile Hepatic bile Gall bladder bile Composition
Concentration Bile salts 1.1 g/dL 6 g/dL Cholesterol 0.1 g/dL g/dL FA 0.12 g/dL g/dL Proteins mg% Lecithin 0.04 g/dL 0.3 g/dL Bilirubin August 3, 2019 Biliary Secretion
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Formation Bile salts Bile acids formed by liver cells from cholesterol
Bile acids which appear in bile as salts of Na+ or K+ Bile acids formed by liver cells from cholesterol Acted by liver enzymes Cholic acid Chenodeoxycholic acid August 3, 2019 Biliary Secretion
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Formation Primary bile acids Secondary bile acids
Formed by the liver cells Secreted into bile Secondary bile acids Formed in the intestinal tract As a result of bacterial action on primary bile acids August 3, 2019 Biliary Secretion
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Conjugation Primary bile acids
Conjugated to amino acids (Taurine, Glycine) Cholic acid Tauro-cholic acid Glyco-cholic acid Chenodeoxycholic acid Tauro-chenodeoxycholic acid Glyco-chenodeoxycholic acid August 3, 2019 Biliary Secretion
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Conjugation The conjugated bile acids Combine with Na+, K+
Form bile salts August 3, 2019 Biliary Secretion
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Conjugation In the intestines Bile salts acted on by bacteria
De-conjugation De-hydroxylation Form secondary bile acids Deoxycholic acid, Lithocholic acid Lithocholic acid bound to intestinal microorganisms Excreted in faeces August 3, 2019 Biliary Secretion
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Formation of Bile Secretin GB August 3, 2019 Biliary Secretion
Bile acids Electrolytes Bilirubin, cholesterol phospholipids drugs, hormones H2O Active secretion active secretion passive diffusion Hepotocytes and Canaliculus Secretion H2O, electrolytes Na+, HCO3- > Cl- Secretin Bile ducts and gall bladder GB Absorption H2O, electrolytes Absorption BILE FLOW H2O, Na+, Cl-, HCO3- August 3, 2019 Biliary Secretion
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Gallbladder Emptying Presence of food in upper GIT
Presence of fatty food in duodenum Causes gallbladder emptying Bile acids via blood stream Stimulate parenchymal cells to secrete bile salts Secretin via blood stream Stimulate ductal cells to secrete water & electrolyte Rich in HCO3- August 3, 2019 Biliary Secretion
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Gallbladder Emptying CCK via blood stream causes
Gallbladder contraction Relaxation of sphincter of oddi Vagal stimulation causes Weak contration of gallbladder August 3, 2019 Biliary Secretion
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Enterohepatic Circulation
0.3 – 0.6 gm/d Circulation of bile salts from liver to intestines and back again to liver From liver to duodenum Common bile duct At the terminal ileum Reabsorption into portal system Synthesis Absorption Secretion Storage 0.3 – 0.6 g Pool 2-3 gm Lost 5% Terminal ileum 95% August 3, 2019 Biliary Secretion
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Enterohepatic Circulation
0.3 – 0.6 gm/d In the liver Extracted from portal circulation Secreted once again Bile salt reabsorbed Synthesis Absorption Secretion Storage 0.3 – 0.6 g Pool 2-3 gm Lost 5% Terminal ileum 95% August 3, 2019 Biliary Secretion
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Enterohepatic Circulation
0.3 – 0.6 gm/d 90 – 95 % of bile salts reabsorbed Diffusion in early portion of SI By active transport at terminal ileum Remaining excreted into feces Synthesis Absorption Secretion Storage 0.3 – 0.6 g Pool 2-3 gm Lost 5% Terminal ileum 95% August 3, 2019 Biliary Secretion
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Enterohepatic Circulation
0.3 – 0.6 gm/d Total pool of circulating bile salts Primary & Secondary Is approx 3.6 gm About 4 – 8 gm of bile salts Required to digest and absorb fat Hence the total pool must circulate more than once Synthesis Absorption Secretion Storage 0.3 – 0.6 g Pool 2-3 gm Lost 5% Terminal ileum 95% August 3, 2019 Biliary Secretion
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Synthesis and Replacement
0.3 – 0.6 gm/d Rate of synthesis determined by Rate of return to liver Normal rate is about 0.3 to 0.6 g/day This replaces normal fecal loss Synthesis Absorption Secretion Storage 0.3 – 0.6 g/d Pool 2-3 gm Lost 5% Terminal ileum 95% August 3, 2019 Biliary Secretion
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