Bile, gallbladder and gallstones Flashcards
What is bile?
A substance produced by the liver that breaks up fat particles.
What is the role of the gallbladder?
Stores and concentrates bile
concentrates it as epithelial cells reabsorb water and electrolytes e.g. Na+ for H+. H2O follows Na+
Therefore, bile becomes more acidic
What are Cholangiocytes?
Epithelial cells of hepatic ductules that modify the composition of bile:
- remove glucose because too much glucose could result in bacteria
- secrete IgA for mucosal protection and HCO3- in response to secretin in post prandial period
Describe the flow of bile.
> Hepatocytes
Bile Canaliculi (merge to form ductules)
Terminal bile ducts
Hepatic Ducts (left and right) > CBD
What do bile salts consist of?
Bile acid + Cation e.g. Na+
What are the Components of bile?
Components of bile are secreted by 2 cell types:
Hepatocytes secrete:
-choleterol, lecithin, phospholipids, bile acids, bile pigments (bilirubin, biliverdin, urobilin etc)
Cholangiocytes of bile ducts secrete:
-bicarbonate rich salt solution (influence by secretin)
When is secretion of bile greatest?
During and after a meal
What is Sphincter of Oddi?
hepatopancreatic sphincter
contracts when fasting
relaxes during and after meals
What happens to the Sphincter of Oddi during interdigestive period?
During interdigestive period, Sphincter of Oddi is contracted, preventing bile from flowing out into duodenum
Pressure increases in CBD and bile flows into gallbladder where it is stored
What is the Composition of hepatic bile?
97% water Cholesterol Lecithin Bile Acids Bile Pigments
What is the Composition of gallbladder bile?
89% water
HCO3- Cl- Ca2+ Mg2+ Na+ Cholesterol Bilirubin Bile salts
Bile is concentrated in gallbladder as NaCl and H20 are lost, increasing solid content.
What does synthesis of bile start from?
Cholesterol breakdown
What are Bile Acids?
Made from cholesterol and secreted into bile and conjugated to glycine or taurine
Why are bile acids conjugated?
increases ability to be secreted and reabsorbed and also decreases their cytotoxicity`
Give 4 major bile acids.
PRIMARY BILE ACIDS (formed in liver)
- cholic acid (50%)
- chenodeoxycholic acid (30%)
SECONDARY BILE ACIDS (formed in the colon)
- Deoxycholic Acid (15%)
- Lithocholic Acid (5%)
What converts primary bile acids into secondary bile acids?
Intestinal bacteria
Cholic acid is converted to Deoxycholic Acid
Chenodeoxycholic acid is converted to Lithocholic acid
What are the Main functions of bile/bile acids?
1) Elimination of cholesterol to bile acids (some excreted in faeces)
2) Reduce precipitation of cholesterol in gallbladder (preventing gallstones)
3) Facilitate absorption of fat soluble vitamins (ADEK)
4) Regulate their own transport and metabolism via enterohepatic circulation
5) Facilitate digestion of triglycerides via emulsification
Describe he Contraction of Gallbladder for Bile Acid Release.
Bile Acid release similar to gastric acid release
1) Cephalic Phase (vagal innervation from dorsal vagal complex stimulates gallbladder contraction)
2) Gastric Phase (vagal innervation from dorsal vagal complex stimulates gallbladder contraction)
3) Intestinal Phase (most gallbladder emptying, stimulated by CCK and secretin)
Describe the Relaxation of Sphincter of Oddi.
Distention of duodenum will send signals via vagal afferents to the dorsal vagal complex. Signals return via efferents, the relaxation of sphincter of Oddi occurs via NO and VIP
Describe the Enterohepatic Circulation of Bile.
Most bile salts are reabsorbed into the intestinal capillaries by Na+-bile salt coupled transporters in the terminal ileum.
Bile salts are then returned to liver via hepatic portal vein and secreted again into bile
What happens during Interruption of enterohepatic circulation?
Excess synthesis of bile salts by liver (as you would be losing bile salts)
Kidneys will excrete the synthesised bile salts (and some cholesterol)
What are Gallstones (cholelithiasis)?
Cholesterol excess causes crystallisation
Causes of excess cholesterol in bile:
- liver secretes excess cholesterol
- reabsorption of salt and water
What are the 2 types of gallstones?
Cholesterol stones
Calcium bilirubinate stones
What are the factors involved in gallstone formation?
Bile stasis
Malabsorption of Bile Acids and Phospholipids
Chronic Infection (bacteria help in pigment stone formation)
Super-saturation of bile with cholesterol
How are gallstones diagnosed?
Ultrasonography and CT
Cholescintigraphy
Endoscope Retrograde Cholangiopancreatography (ERCP)
Give Clinical Features of Gallstones.
85% tend to be asymptomatic if stones are small
If neck of cystic duct is blocked, acute cholecystitis develops, which can lead to cholestatic jaundice, which leads to cholangitis (bacterial infection) due to any glucose present
