Gall bladder and bile

Question 1

Functions of bile

Answer 1

Cholesterol homeostasis
Absorption of vitamins/dietary lipids
Toxin excretion eg cholesterol metabolites, adrenocortical, and other steroid hormones

Question 2

What substances are secreted into bile

Answer 2

Adrenocortical and other steroid hormones
Drugs/xenobiotics
Cholesterol
Alkaline phosphatase

Question 3

What colour is bile and why is it that colour?

Answer 3

billirubin and biliverdin make it yellow/green

Question 4

What secretes bile?

Answer 4

Hepatocyes - liver cells

Cholangiocytes - biliary epithelial cells

Question 5

What drains bile? Through what?

Answer 5

Bile drains from liver
through bile ducts
into duodenum
at duodenal papilla

Question 6

How much bile is secreted daily?

Answer 6

500ml

In average healthy adult

Question 7

What does bile produced in cholangiocytes do?

Answer 7

alters pH
water moves into bile via osmosis
reabsorption of sugars and acids
secretion of HCO3- and Cl-
IgA exocytosed

Question 8

How is biliary excretion of bile salts and toxins performed?

Answer 8

By transporters on apical surface of hepatocytes + cholangiocytes

Question 9

What else do biliary transports also goven?

Answer 9

Rate of bile flow

Question 10

What does a dysfunction in biliary transporters lead to

Answer 10

Cholestasis

Question 11

What are the main transporters of bile?

Answer 11

• bile salt excretory pump (BSEP)
• MDR related proteins (MRP1 and MRP3)
• products of the familial intrahepatic cholestasis gene

Question 12

How much bile is made from the hepatocytes and the cholangiocytes?

Answer 12

Hepatocytes 60%

Cholangiocytes 40%

Question 13

What does the BSEP bile transporter do?

Answer 13

Active transport of bile acids across hepatocyte canalicular membranes into bile, and secretion of bile acids is a major determinant of bile flow

Question 14

What does the MDR1 bile transporter do?

Answer 14

Mediates canalicular excretion of xenobiotics and cytotoxins

Question 15

What does the MDR3 bile transporter do?

Answer 15

Encodes a phospholipid transporter protein that translocates phosphatidylcholine from inner to outer leaflet of canalicular membrane

Question 16

What are bile salts?

Answer 16

Sodium and potassium salts of bile acids

Question 17

What are bile acids synthesised from?

Answer 17

Cholesterol

Question 18

What are the two primary bile acids? Where are they made?

Answer 18

In liver by hepatocytes
Cholic acid
Chenodeoxycholic acid

Question 19

What are the two secondary bile acids? How are they made

Answer 19

Deoxycholic acid
Lithocholic acid
Converted by gut bacteria from primary bile acids

Question 20

What do bile salts do?

Answer 20

Reduce surface tension of fats

Emulsify fat preparatory to its digestion/absorption

Question 21

How do bile salts form micelles?

Answer 21

Bile salts amphipathic
One surface has hydrophilic domains - facing out
2nd has hydrophobic domains facing in
free fatty acids and cholesterol inside
thus transported into GIT epithelial cells for absorption

Question 22

What’s the problem with bile salts?

Answer 22

The detergent like actions make bile salts potentially cytotoxic in high concentrations
Can cause gut irritation/diarrhoea if not reabsorbed properly

Question 23

How is the ampulla of the bile duct controlled?

Answer 23

Sphincter of Oddi

Circular muscle that opens and closes

Question 24

What does the ampulla of bile do?

Answer 24

Let bile from the common bile duct enter the duodenum

Question 25

What does cholecystokinin do?

Answer 25

When you eat it is released Causes sphincter of oddi to relax, opening the hole Causes gall bladder to squeeze and pump into duodenum Bile there to help digest fat

Question 26

Anatomy of biliary system

Answer 26

Each hepatocyte apposed to several bile canaliculi These drain into intralobular bile ducts coalesce into interlobular ducts form right and left hepatic duct join outside liver to form common hepatic duct Cystic duct drains the gall bladder and unites with the common hepatic duct to form common bile duct CBD joined by pancreatic duct before entering duodenal papilla

Question 27

Where does bile go between meals? How does this happen?

Answer 27

Bile divered into gall bladder for storage | Duodenal orifice closed dur to sphincter of Oddi contracted

Question 28

What percentage of bile salts are reabsorbed and undergo enterohepatic circulation

Answer 28

95% absorbed from small terminal ileum

Question 29

How do bile salts go through the enterohepatic circulation?

Answer 29

By Na+/bile salt co-transport Na+/K+ ATPase system 5% converted into secondary bile acids in the colon Deoxycholate absorbed lithocholae 99% excreted in stool Absorbed bile salts go through portal vein back to liver and re-excreted in bile

Question 30

What happens in terminal ileal resection/disease?

Answer 30

``` Less bile salt reabsorption more stool (fat) bc enterohepatic circulation interrupted and liver can't increase rate of bile salt production enogh to make it up ```

Question 31

What would happen if bile stopped entering the gut

Answer 31

Up to 50% ingested fat appears in faeces | Malabsorption of fat soluble vitamins A,D,E,K

Question 32

What does the gall bladder do?

Answer 32

Stores bile - 50ml and released after meal for fat digestion Acidifies bile Concentrates bile by H2O diffusion following net absorption of Na+, Cl-, Ca2+, HCO3- (intra-cystic pH) gall bladder can reduce volume of stored bile by 80-90%

Question 33

What happens if a patient gets a cholecystectomy?

Answer 33

Periodic discharge of bile from gallbladder aids digestion but is not essential Normal health and nutrition exists with continuous slow bile discharge from duodenum Avoid food with high fat content