Liver Structure and Function Flashcards
Describe the composition and function of bile, the mechanisms controlling its storage and release from the gallbladder and the mechanism whereby it is reabsorbed.
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Describe the anatomy of the liver.
- Largest organ in body: approx. 1.4kg (3lb)
- Located in upper right quadrant of abdomen (tucked against inferior surface of diaphragm).
- 2 major lobes: right > left.
- 2 minor lobes: caudate, quadrate.
- Entry/exit of blood vessels (hepatic portal vein, hepatic artery), lymphatic vessels, ducts (right/left hepatic ducts –> common hepatic duct), nerves (hepatic nerve plexus) via porta on inferior surface.
- Common hepatic duct joined by cystic duct from gallbladder –> common bile duct + pancreatic duct –> major duodenal papilla (Sphincter of Oddi).
Describe the histology of the liver.
- Liver covered by connective tissue capsule and visceral peritoneum except for bare area (small area on diaphragmatic surface surrounded by coronary ligament – connects liver to diaphragm).
- At porta, connective tissue capsule becomes branching network of septa into body of liver providing support.
- Vessels, ducts and nerves follow septa throughout liver.
- Septa divide liver into hexagonal lobules.
- Portal triad (hepatic portal vein, hepatic artery, hepatic duct) located at each corner of hexagonal lobule (also nerves and lymph vessels).
- Central veins at centre of each lobule –> hepatic veins –> inferior vena cava.
- Hepatic cords (composed of hepatocytes) radiate out from central veins.
- Bile canaliculus (cleft-like lumen) lied between cells within each cord.
- Hepatic sinusoids: spaces (blood channels) between hepatic cords.
Describe the function of the liver.
- Hepatocytes: bile synthesis, nutrient storage (glycogen, fats, vitamins (B12, A, D, E, K), Cu, Fe), nutrient interconversion, detoxification.
Six components of bile;
- Bile acids, lecithin, cholesterol: synthesised in liver, solubilise fat.
- Bile pigments: bilirubin (from haemoglobin).
- Toxic metals: detoxified in liver.
- Bicarbonate: neutralisation of acid chyme.
1 –> 5 secreted by hepatocytes.
HCO3 secreted by duct cells.
Describe bile pigments.
- Breakdown of products of haemoglobin from old/damaged erythrocytes.
- Bilirubin (predominant bile pigment): extracted from blood by hepatocytes and secreted into bile –> yellow bile.
- Bilirubin modified by bacterial enzymes –> brown faeces.
- Reabsorbed bilirubin excreted in urine –> yellow urine.
Describe the synthesis and secretion of bile acids.
- Synthesised in lover from cholesterol (0.5g/day).
- Before secretion, bile acids conjugated with glycine or taurine –> bile salts (increase in solubility).
- Secreted bile salts recycled via enterohepatic circulation.
Liver –> bile duct –> duodenum –> ileum –> hepatic portal vein –> liver…
Describe the control of bile secretion.
Sphincter of Oddi;
- Controls release of bile and pancreatic juice into duodenum.
- When contracted (closed) –> bile forced back into gallbladder.
- Gallbladder concentrates bile 5-20 times (absorbs Na and H2O).
- Fat in duodenum –> release of CCK –> Sphincter of Oddi relaxes, gallbladder contracts (stimulates secretion of secretin from acinar cells).
Describe the control of bile secretion.
Sphincter of Oddi;
- Controls release of bile and pancreatic juice into duodenum.
- When contracted (closed) –> bile forced back into gallbladder.
- Gallbladder concentrates bile 5-20 times (absorbs Na and H2O).
- Fat in duodenum –> release of CCK –> Sphincter of Oddi relaxes, gallbladder contracts (stimulates secretion of secretin from acinar cells –> pancreatic enzyme and bile secretion).
Summarise the actions of secretin.
Acid in duodenum –> secretin –>
- Decrease in gastric acid secretion
- Decrease in gastric emptying
- Increase in duodenal HCO3 secretion
- Increase in pancreatic HCO3 secretion
- Increase in bile duct HCO3 secretion
- -> neutralisation
Summarise the actions of cholecystokinin (CCK).
Fat/amino acids in duodenum –> CCK –>
- Decrease in gastric emptying
- Increase in pancreatic enzyme secretion
- Gallbladder contraction
- Relaxation of Sphincter of Oddi
- -> digestion
