Bile, gallbladder and gallstones

Question 1

What is bile?

Answer 1

A substance produced by the liver that breaks up fat particles.

Question 2

What is the role of the gallbladder?

Answer 2

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

Question 3

What are Cholangiocytes?

Answer 3

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

Question 4

Describe the flow of bile.

Answer 4

> Hepatocytes
Bile Canaliculi (merge to form ductules)
Terminal bile ducts
Hepatic Ducts (left and right) > CBD

Question 5

What do bile salts consist of?

Answer 5

Bile acid + Cation e.g. Na+

Question 6

What are the Components of bile?

Answer 6

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)

Question 7

When is secretion of bile greatest?

Answer 7

During and after a meal

Question 8

What is Sphincter of Oddi?

Answer 8

hepatopancreatic sphincter

contracts when fasting
relaxes during and after meals

Question 9

What happens to the Sphincter of Oddi during interdigestive period?

Answer 9

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

Question 10

What is the Composition of hepatic bile?

Answer 10

97% water
Cholesterol
Lecithin
Bile Acids
Bile Pigments

Question 11

What is the Composition of gallbladder bile?

Answer 11

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.

Question 12

What does synthesis of bile start from?

Answer 12

Cholesterol breakdown

Question 13

What are Bile Acids?

Answer 13

Made from cholesterol and secreted into bile and conjugated to glycine or taurine

Question 14

Why are bile acids conjugated?

Answer 14

increases ability to be secreted and reabsorbed and also decreases their cytotoxicity`

Question 15

Give 4 major bile acids.

Answer 15

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%)

Question 16

What converts primary bile acids into secondary bile acids?

Answer 16

Intestinal bacteria

Cholic acid is converted to Deoxycholic Acid

Chenodeoxycholic acid is converted to Lithocholic acid

Question 17

What are the Main functions of bile/bile acids?

Answer 17

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

Question 18

Describe he Contraction of Gallbladder for Bile Acid Release.

Answer 18

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)

Question 19

Describe the Relaxation of Sphincter of Oddi.

Answer 19

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

Question 20

Describe the Enterohepatic Circulation of Bile.

Answer 20

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

Question 21

What happens during Interruption of enterohepatic circulation?

Answer 21

Excess synthesis of bile salts by liver (as you would be losing bile salts)

Kidneys will excrete the synthesised bile salts (and some cholesterol)

Question 22

What are Gallstones (cholelithiasis)?

Answer 22

Cholesterol excess causes crystallisation

Causes of excess cholesterol in bile:

• liver secretes excess cholesterol
• reabsorption of salt and water

Question 23

What are the 2 types of gallstones?

Answer 23

Cholesterol stones

Calcium bilirubinate stones

Question 24

What are the factors involved in gallstone formation?

Answer 24

Bile stasis

Malabsorption of Bile Acids and Phospholipids

Chronic Infection (bacteria help in pigment stone formation)

Super-saturation of bile with cholesterol

Question 25

How are gallstones diagnosed?

Answer 25

Ultrasonography and CT

Cholescintigraphy

Endoscope Retrograde Cholangiopancreatography (ERCP)

Question 26

Give Clinical Features of Gallstones.

Answer 26

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