functions of bile salts

Functions of Bile Salts

Ayesha Akhtar

Liver• Location

• R. Hypochondrium• Epigastric region

• 4 Lobes• Left • Quadrate• Caudate• Right

• Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

What is Bile?

What is Bile?

Bile is • Dark green to yellowish brown viscous fluid • Secreted by Liver parenchymal cells (Hepatocytes)• Through bile Canaliculi (network of space between

Hepatocytes) and bile duct and • is stored in gallbladder • 500-1000ml (approx) of bile is secreted per day by liver

Composition of Bile

It contains• 97% water• 3% solids (75% of it is organic matter & rest is

inorganic salts)

Organic matter consist of,• Bile salts• Mucin• Bile pigments• Lipids( including fats, fatty acids, phospholipids

& cholesterol)

Inorganic part consist of Ions of Na, K, HCO3, Cl

Bile acids from cholesterol

• formed from cholesterol in the liver

• stored in the gall bladder in bile as bile salts (sodium and potassium)

• utilized during digestion of fats and other lipid substances (act as detergents)

CholateCholateCholateCholateCholesterolCholesterolCholesterolCholesterol

CholesterolCholesterol77-hydroxylase-hydroxylase

CholesterolCholesterol77-hydroxylase-hydroxylase

Cholate & Chenodeoxycholate are primary bile salts

Approximate composition of bile salts• Glycocholate – 24%• Glycochenodeoxycholate – 24%• Taurocholate – 12%• Taurochenodeoxycholate – 12%• Glycodeoxycholate -- 16%• Taurodeoxycholate – 8%• Various lithocholate – 4%

Properties of Bile salts

• detergent character of bile salts is due to the hydrophobic-hydrophilic nature of the molecules

• the presence of hydroxyl (or sulfate) and the terminal carboxyl group on the tail gives the molecule its hydrophilic face

• the steroid ring provides the hydrophobic face

• 3-4 grams present in blood which undergoes enterohepatic circulation 6-8 times/day

Function of bile salts

Emulsification of fats due to detergent activity Decreasing surface tension Emulsify fats, which is a prerequisite for the action of

pancreatic lipase Accelerating the action of pancreatic lipase Aid in the absorption of fat-soluble vitamins that

include, Keep cholesterol in solution (as micelles) Choleretic action Solubility of cholesterol Antiseptic effect

Function of bile salts

Emulsification of fats due to detergent activity Accelerating the action of pancreatic lipase In the presence of bile salts, Colipase binds to lipase, shifting pH pf enzyme from 9.0 to 6.0 Aid in the absorption of fat-soluble vitamins that

include,

Keep cholesterol in solution (as micelles) Choleretic action Solubility of cholesterol Antiseptic effect

Function of bile salts

Emulsification of fats due to detergent activity Accelerating the action of pancreatic lipase Aid in the absorption of fat-soluble vitamins that

include, Vitamin A, D, E and K Its also absorb carotene Keep cholesterol in solution (as micelles) Choleretic action Solubility of cholesterol Antiseptic effect

Function of bile salts

Emulsification of fats due to detergent activity Accelerating the action of pancreatic lipase Aid in the absorption of fat-soluble vitamins that

include, Keep cholesterol in solution (as micelles) forms ‘micelles’ with fatty acid, mono & diacyl glycerol &

also TG making them water soluble and helps it in absorption

Choleretic action Solubility of cholesterol Antiseptic effect

Function of bile salts

Emulsification of fats due to detergent activity Accelerating the action of pancreatic lipase Aid in the absorption of fat-soluble vitamins that

include, Keep cholesterol in solution (as micelles) Intestinal motility Choleretic action stimulate liver to secrete more bile salts Solubility of cholesterol Antiseptic effect

Function of bile salts

Emulsification of fats due to detergent activity Accelerating the action of pancreatic lipase Aid in the absorption of fat-soluble vitamins that

include, Keep cholesterol in solution (as micelles) Intestinal motility Choleretic action Solubility of cholesterol Keep cholesterol in solution

Function of bile salts

Emulsification of fats due to detergent activity Accelerating the action of pancreatic lipase Aid in the absorption of fat-soluble vitamins that

include, Keep cholesterol in solution (as micelles) Intestinal motility Choleretic action Solubility of cholesterol Antiseptic effect

CholesterolCholesterolCholesterolCholesterol

Bile SaltBile SaltBile SaltBile Salt

PhospholipidPhospholipidPhospholipidPhospholipid

Structure of Biliary and Intestinal Structure of Biliary and Intestinal MicellesMicelles

Functions of Micelles

• Transport cholesterol from the liver into the intestine via the biliary tree

• Participate in fat digestion and absorption

Biliary Lipid Secretion

Sinusoidal Membrane

BloodBloodBloodBlood HepatocyteHepatocyteHepatocyteHepatocyte

Canalicular Membrane

Bile SaltBile SaltBile SaltBile Salt

ABCG5/G8Cholesterol

ABCB4Phospholipid

ABCB11

BileBileBileBile

Clinical Aspects

• Liver test Bile salts are greatly increased in obstructive jaundice and are used

as diagnostic tests for it

• GallstonesIn the absence of bile salts, cholesterol may be precipitated as

‘Gallstones’

References

1. Essentials of Biochemistry

by Mushtaq Ahmad

2. Textbook of Medical Biochemistry

by MN Chatterjea & Rana Shinde