L24 - liver anatomy & function
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can the liver regenerate?
yes
mass of liver
approx 1.5kg
describe liver structure
• 4 lobes (left, right, caudate, quadrate) NOTE: opposite way on diagrams • diaphragmatic surface superior upper surface of the liver • visceral surface faces abdominal organs (where gallbladder is located)
what is the liver made up of?
• lobules • containing hepatocytes + kupffer cells • blood vessels (sinusoids) • bile caniculi
what is the portal triad?
• bile duct • hepatic portal vein • hepatic artery
describe liver blood flow
• liver receives blood from the heart & GI tract • hepatic portal VEIN delivers deoxygenated blood from GI tract • hepatic artery delivers oxygenated blood from heart • the artery + vein divide into 2 and supply the left + right side of the liver • blood flows from hepatic portal vein and hepatic artery through lobules into central vein • bile flows in opposite direction
what are the exocrine (digestive) functions of the liver?
• secretes bile salts and HCO3- • involved in cholesterol metabolism • organic and drug metabolism
endocrine functions of liver
• secretes peptides & hormoes • clotting and produces plasma clotting factors • secretes plasma proteins
where is bile synthesised and stored?
synthesised in liver by HMG-CoA, stored in gallbladder
hepatocytes and their function in bile (exocrine function)
• create bile salts to solubilise fats • cholesterol • phospholipids (lectin) • bile pigments ( extracts billirubin from rbc)
epithelial cells and their function in bile (exocrine function)
• HCO3- neutralises stomach acid • secretion is triggered by secretion from small intestine in response to fatty acids in diet
during a meal what does the gallbladder do?
• contracts • release bile into duodenum (SI) • via Sphincter of Oddi
what is the contraction of gallbladder stimulated by during a meal?
cholecytoskinin from SI which is triggered by fatty acids
enterohepatic circulation
• flow of bile / bile salts • release of bile. bile salts from gallbladder • during fatty meal, bile salts are absorbed in SI but Na+ coupled transporters • 95% is retired back to liver through hepatic portal vein: enterohepatic circulation • hepatocytes absorb bile salts from blood and secrete back into the bile • 5% lost in faeces and new bile salts synthesised from cholesterol
what are new bile salts synthesised from?
cholesterol
what does the liver do with cholesterol?
• extracts cholesterol from blood and secretes it into the bile and faeces • can use to make more bile
describe cholesterol
• insoluble • froms micelles • forms lipoproteins in plasma
what happens when we eat dietary fibre?
• hides bile in SI preveting enterhepatic circulation (bile doesn’t return to liver through hepatic portal vein). • so it removes the bile from the body and the cholesterol it contains
can cholesterol lower drugs?
yes
why do we need cholestrol?
• membrane + bile synthesis • precursor to steroid hormones • taken up by cells from blood for use
how does the liver use bile?
extracts cholesterol and secretes it into bile or metabolises it into bile salts
how are levels of cholesterol balance maintained?
increased dietary cholesterol suppresses HMG-CoA
bad cholesterol (LDL)
saturated fatty acids - red meat - cheese - whole milk increases plasma cholesterol
good cholesterol (HDL)
• polyunsaturated/ monounsaturated • olive / peanut oil decreases plasma conc