Gall bladder and bile Flashcards
Functions of bile
Cholesterol homeostasis
Absorption of vitamins/dietary lipids
Toxin excretion eg cholesterol metabolites, adrenocortical, and other steroid hormones
What substances are secreted into bile
Adrenocortical and other steroid hormones
Drugs/xenobiotics
Cholesterol
Alkaline phosphatase
What colour is bile and why is it that colour?
billirubin and biliverdin make it yellow/green
What secretes bile?
Hepatocyes - liver cells
Cholangiocytes - biliary epithelial cells
What drains bile? Through what?
Bile drains from liver
through bile ducts
into duodenum
at duodenal papilla
How much bile is secreted daily?
500ml
In average healthy adult
What does bile produced in cholangiocytes do?
alters pH water moves into bile via osmosis reabsorption of sugars and acids secretion of HCO3- and Cl- IgA exocytosed
How is biliary excretion of bile salts and toxins performed?
By transporters on apical surface of hepatocytes + cholangiocytes
What else do biliary transports also goven?
Rate of bile flow
What does a dysfunction in biliary transporters lead to
Cholestasis
What are the main transporters of bile?
- bile salt excretory pump (BSEP)
- MDR related proteins (MRP1 and MRP3)
- products of the familial intrahepatic cholestasis gene
How much bile is made from the hepatocytes and the cholangiocytes?
Hepatocytes 60%
Cholangiocytes 40%
What does the BSEP bile transporter do?
Active transport of bile acids across hepatocyte canalicular membranes into bile, and secretion of bile acids is a major determinant of bile flow
What does the MDR1 bile transporter do?
Mediates canalicular excretion of xenobiotics and cytotoxins
What does the MDR3 bile transporter do?
Encodes a phospholipid transporter protein that translocates phosphatidylcholine from inner to outer leaflet of canalicular membrane
What are bile salts?
Sodium and potassium salts of bile acids
What are bile acids synthesised from?
Cholesterol
What are the two primary bile acids? Where are they made?
In liver by hepatocytes
Cholic acid
Chenodeoxycholic acid
What are the two secondary bile acids? How are they made
Deoxycholic acid
Lithocholic acid
Converted by gut bacteria from primary bile acids
What do bile salts do?
Reduce surface tension of fats
Emulsify fat preparatory to its digestion/absorption
How do bile salts form micelles?
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
What’s the problem with bile salts?
The detergent like actions make bile salts potentially cytotoxic in high concentrations
Can cause gut irritation/diarrhoea if not reabsorbed properly
How is the ampulla of the bile duct controlled?
Sphincter of Oddi
Circular muscle that opens and closes
What does the ampulla of bile do?
Let bile from the common bile duct enter the duodenum
What does cholecystokinin do?
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
Anatomy of biliary system
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
Where does bile go between meals? How does this happen?
Bile divered into gall bladder for storage
Duodenal orifice closed dur to sphincter of Oddi contracted
What percentage of bile salts are reabsorbed and undergo enterohepatic circulation
95% absorbed from small terminal ileum
How do bile salts go through the enterohepatic circulation?
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
What happens in terminal ileal resection/disease?
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
What would happen if bile stopped entering the gut
Up to 50% ingested fat appears in faeces
Malabsorption of fat soluble vitamins A,D,E,K
What does the gall bladder do?
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%
What happens if a patient gets a cholecystectomy?
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
