Physio 7: Liver Flashcards
What are the five functions of the liver?
- Metabolic - carbohydrate, protein, lipid, cholesterol synthesis
- Storage - glycogen, fat soluble vitamins ADEK, vitamin B12, minerals (iron, copper)
- Detoxification - using phase I and II conjugating enzymes
- Synthesis of important components - plasma proteins, coagulation factors, apolipoproteins, angiotensinogen
- Excretion - breakdown products of heme to form bilirubin, cholesterol converted to bile to be excreted, urea from AAs/ammonia
What are somatomendins?
Group of proteins that promote cell division/growth
What two things increase synthesis of somatomendins by the liver?
Growth hormone and somatotropin
What are the five functions of bile acids?
- Emulsification of TAGs
- Help in absorption - fat-soluble vitamins
- Increase solubility - prevents precipitation of cholesterol
- Excrete cholesterol, partly as bile acids
- Act as hormones - bind to nuclear receptors and alter protein expression in cholesterol homeostasis
What comprises bile secretions?
- Bile acids - emulsify fat by forming micelles
- Phospholipids
- Cholesterol
- Bile pigments (breakdown of heme)
- Inorganic ions - HCO3-
- Detoxified foreign cmpds and drugs
- Protein products
Describe 4 main steps of formation of bile.
- Hepatocytes secrete bile into canaliculi
- Bile ducts secrete watery, HCO3-rich fluid into bile
- Diluted hepatic bile mixes with concentrated gallbladder bile
- Between meals, part of bile goes back into GB where it gets concentrated (removes water and electrolytes) and stored
What percentage of bile acids secreted are from a recirculating pool?
90%
Are bile acids conjugated or unconjugated? Salts?
What is used for conjugation? Which AA makes them?
Acids - unconjugated
Salts - conjugated
Glycine and taurine are used - made by cysteine
What is more effective in emulsification? Salts or acids? Why?
Salts - hydrophobic surfaces can be accessed by lipases
Where do primary bile salts come from?
Made in liver from cholesterol through 7-alpha hydroxylase, recovered by ATP-dep transport
Where do secondary bile salts come from? What happens to them in the ileum?
They are primary bile salts modified in GI tract by bacteria - recovered by Na+ gradient-dependent transport through diffusion
In ileum, they are converted to unconjugated bile acids for reuptake into portal circulation
Where do tertiary bile salts come from?
Formed from secondary bile salts and recovered by OH- or HCO3- dependent anion exchange
What hormones increase bile secretion?
CCK, motilin
What hormones increase HCO3- secretion from cholangiocytes?
Secretin, glucagon, VIP
What reduces HCO3- secretion?
Somatostatin
