Liver Physiology Flashcards
Normal blood supply to the liver?
Oxygenated blood from the hepatic artery and deoxygenated blood from the hepatic portal vein
Aorta > Coeliac trunk > Hepatic artery proper > R&L hepatic arteries
What makes up the portal triad?
Hepatic artery
Hepatic portal vein
Bile duct
What’s the Pringle manoeuvre?
Pinch the free edge of the lesser momentum (containing portal triad) to cut off bloody supply during surgery
Outline the organisation of the liver
Hepatocytes arranged in hexagonal lobules each with a portal triad
Within each lobule hepatocytes are arranged in plates, in a reticuloendothelial cell cage
Hepatocyte plates separated by sinusoids, draining blood into central veins, which converge to the hepatic vein
Outline the functional zonation of liver lobules
Zone 1 (periportal) - most oxygenated so specialised in metabolism (oxidative metabolism, gluconeogenesis and urea synthesis)
Zone 3 (pericentral) - specialised for drug metabolism, glycolysis and lipogenesis
What are the major cell types of the liver?
Hepatocytes = main functional units
Cholangiocytes = secrete HCO3- and H20 (line bile duct)
Reticuloendothelial cell cages lining hepatocyte plates are made of: Endothelial cells Kupffer cells (immune function) Lipocytes (Stellate cells)
What are the major functions of the liver?
Drug metabolism & detoxification Energy metabolism & substrate interconversion Synthesis of plasma proteins Production of bile Immune function Cholesterol processing Excretion of bile Storage of vitamins & minerals
What plasma proteins are produced by the liver?
Albumin
Fibrinogen and Plasminogen for haemostasis
Thyroid binding globulin, SHBG
What are the 6 main components of bile and what is its function?
Aids digestion by neutralising acid and emulsifying lipids (it’s amphiphilic)
Bile salts Lecithin (Phospholipid) HCO3- and other salts Cholesterol Bile pigments Trace metals
What’s the role of the gallbladder with regards to bile production?
Liver produces bile which is stored and concentrated in the gallbladder
Absorbs H20 and salts to concentrate
CCK stimulates gallbladder to contract to release bile into duodenum via common bile duct
What do hepatocytes and cholangiocytes secrete to form bile?
Hepatocytes: Bile salts Cholesterol Bile pigments Lecithin
Cholangiocytes:
HCO3-
H20
Bile salts = (primary and secondary)
Primary bile salts = cholesterol + taurine
Secondary bile salts = cholesterol + glycine
What’s the significance of the enterohepatic circulation?
Bile salts are released into the small intestine
95% of them will be recycled via the enterohepatic circulation and returned to the liver for reuse
5% will be excreted in faeces and will need to be replaced
Of the 95% recycled primary bile salts, 75% are intact but 25% are deconjugated. Explain this
Some bile salts will be deconjugated in the terminal ileum by bacteria into primary bile acids and some are dehydroxylated into secondary bile acids
They then become deconjugated with taurine/glycine and process starts again
What’s the function of bile salts?
Emulsify dietary lipids so they can be digested by pancreatic lipase
Elimination of cholesterol
Prevention of cholesterol precipitation in the gallbladder
Facilitates absorption of fat soluble vitamins
What are the functions of cholesterol? (Lipid molecule)
Plasma membranes
Component of bile salts
Precursor for steroid hormones
Myelin
Majority of cholesterol is synthesised in the liver, small amount from diet intake. What’s the role of the liver in cholesterol processing?
Synthesis from Acetyl CoA
Synthesises lipoproteins, which transport cholesterol in plasma
Exports plasma via circulation for synthesis of steroid hormones
Exports plasma to gallbladder for bile salts
Exports excess cholesterol for excretion in faeces
Extracts excess cholesterol from plasma
What are fat soluble vitamins? That the liver stores
D A K E And minerals
Outline the enterohepatic circulation
Circulation of bile acids, bilirubin, drugs from the liver to bile ending up in the small intestine and being absorbed across enterocytes to be transported back to the liver
Outline the splanchnic circulation
Blood flow through the stomach, small intestine, large intestine, pancreas, spleen and liver
Portal vein carries blood draining from all of these organs
What is ascites and how does it arise in cirrhosis?
Ascites = increased portal pressure and decreased plasma protein content causing transudation of fluid into extracellular space (abdominal cavity)
Decreased plasma Albumin by decreased synthetic function = decreased oncotic pressure of the blood = increased portal pressure
Which metabolites cause hepatic encephalopathy?
Urea and ammonia build up in the blood by loss of urea cycle metabolism in the liver and get to the brain to cause mental confusion
= hallmark of liver failure
What are two tests for synthetic liver function and why?
Albumin - decreased plasma albumin in liver failure due to impaired ability of liver to synthesise plasma proteins
Pro-thrombin time = increased/takes longer for blood to clot due to decreased synthesis of plasma proteins responsible for coagulation (fibrinogen/plasminogen)
Which two liver function tests will be raised by hepatocyte damage and why?
Alanaine Transaminase and Aspartate Transaminase - they’re enzymes in hepatocytes so are released into bloodstream in hepatocyte damage
