GIT Lec 5: Liver + Biliary system Flashcards
The liver
- is the largest internal organ of body (2.5% of body weight)
- contains 4 different lobes
- receives 25% of cardiac output
- extends across the entire abdominal cavity
ducts (liver)
-common hepatic duct –> common bile duct –> pancreatic duct
hepatic lobule is
the building block of the liver
hepatic lobule structure
-hexagonal structure with central vein in the middle, portal triads at each corner
portal triad composed of
hepatic artery, portal vein, bile duct
liver sinusoids
vessels in hepatic lobule in which blood from hepatic artery and portal vein mix
cell types liver
- epithelial cells (hepatocytes- 70%, bile duct epithelium (cholangiocytes)- 3-5%)
- kupffer cells - specialized macrophages
- endothelial cells-lining the sinusoids- “fenestrated”- leaky
major functions of the liver
- exocrine gland: formation + secretion of bile
- metabolism +storage of nutrients (liver matches supply to demain) ex. glucose –> glycogen
- deactivation + detoxification (drugs, hormones, waste, toxicants)
- production of circulating proteins (blood coag factors, lipoproteins)
Constituents of bile
- bile acids
- cholesterol (amphipathic)
- salts (eg. Na+, K+,HCO3-), H2O
- phospholipids (ex. phosphatidyl choline - amphipathic)
- bile pigments (ex. bilirubin- breakdown product of heme)
- trace metals
bile acids synthesized by
hepatocytes from cholesterol–> amphipathic
pancreatic lipase is water soluble so
It works only at surface of lipid droplets
emulsification
-large lipid droplets made into smaller droplets
emulsification requires
- mechanical disruption to make lipid droplets smaller
- emulsifying agents to prevent re-aggregating (amphipathic bile acids/phospholipids)
bile acids and phospholipids +products of lipase digestion which are …. form
- free fatty acids, monoglycerides
- mixed micelles
pure phospholipids can’t form micelles because
steric hindrance
-liposome instead
micelles keep free fatty acids, monoglycerides
in small soluble aggregates —“holding station”
equilibrium between micelle + free fatty acids, monoglycerides (consequence)
free forms diffuse across the small intestine epithelium
formation of bile (cells)
- hepatocytes - produce + secrete bile acids (from cholesterol), secrete phospholipids, cholesterol + bile pigments -primary active transport)
- bile duct cells- HCO3- (and other salts)+ H2O to bile
- gallbladder- stores + concentrates bile between meals +exprels after one
bile acid released amount and in feces (recovery)
- 20-40 g of bile acid released
- 0.5 g in feces (95% recovered)
enterohepatic circulation
recycling of bile acids– reabsorbed in ileum into portal circulation into hepatocytes
- so secretion rate greater than synthesis rate
fibre consequences on enterohepatic circulation
-Sequesters bile acids, lose more to feces and more bile acids created lowering plasma cholesterol
drugs in enterohepatic circulation benefits + disadvantages
benefits: remains in place of action
disadvantages: reduces bioavailability
secretin- regulation of hepatobiliary secretion
increased HCO3- secretion by bile duct cells/pancreas
CCK- regulation of hepatobiliary secretion
increased contraction of gallbladder + relaxes sphincter of Oddi
gallstones (cholesterol stones)- majority
- cholesterol is water-insoluble, kept in solution by micelles
- increases cholesterol in bile to precipitate out (nucleating agent: proteins, bacteria)
gallstones (pigment stones)- less common
- caused by excessive hemolysis
- increased in bile pigments, precipitate out with Ca2+
consequences of gallstones
- may cause obstruction, infection of gallbladder, liver, pancreas
- pain, nausea, jaundice, malabsorption of fat/ fat soluble vitamins
treatment of gallstones
- cholecystectomy (removal of gallbladder)
- removal of stones
- drugs to dissolve stones
bile canaliculus
-thin tubes that receive bile from hepatocytes then drain into cholangiocytes bile duct
