Biliary Secretions August 3, 2019 Biliary Secretion

Functional Anatomy Hepatic artery Sinusoid Portal vein Central vein Bile duct Bile canaliculi August 3, 2019 Biliary Secretion

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

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

Composition Inorganic solutes Na+, K+, Ca++, Mg++, Cl-, HCO3- August 3, 2019 Biliary Secretion

Composition of Bile Hepatic bile Gall bladder bile Composition Concentration Na+ 132-165 meq/L 130 meq/L K+ 4.2-5.6 meq/L 12 meq/L Ca++ 1.2-4.8 meq/L 23 meq/L Mg++ 1.4-3.0 meq/L HCO3- 17-56 meq/L 10 meq/L Cl- 100 meq/L 25meq/L August 3, 2019 Biliary Secretion

Composition of Bile Hepatic bile Gall bladder bile Composition Concentration Bile salts 1.1 g/dL 6 g/dL Cholesterol 0.1 g/dL 0.3-0.9 g/dL FA 0.12 g/dL 0.3-1.2 g/dL Proteins 25-140 mg% Lecithin 0.04 g/dL 0.3 g/dL Bilirubin August 3, 2019 Biliary Secretion

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

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

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

Conjugation The conjugated bile acids Combine with Na+, K+ Form bile salts August 3, 2019 Biliary Secretion

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

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

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

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

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

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

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

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

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