Changes

*Osmotic secretory process

Bile formation is an osmotic secretory process that is driven by the active concentration of bile salts in the bile canaliculi. Various transport mechanisms in the basolateral (sinusoidal) and apical (canalicular) surfaces of the hepatocytes facilitate this active concentration. The rate limiting step in this process is via transport across the canalicular membrane side of the hepatocyte.

*Driven by active concentration of bile salts in the bile canaliculi

*Transport mechanisms in the basolateral (sinusoidal) and apical (canalicular) surfaces of the hepatocytes. There are absolutely stacks of these on both membranes. Transport on the across the canalicular membrane side of the hepatocyte is the rate limiting step.

**Sinusoidal membrane

Within the '''sinusoidal membrane''', Na/K ATPase maintains a –35mV charge which drives several transport mechanisms. The Na/H+ pump drives protons out of the cell whilst HCO3- is exhanged for Na+ facilitating the entry of bicarbonate. Therefore active concentration of bile salts or acids is Na+ dependent.

***Na/K ATPase maintains –35mV charge which drives the Na/H+ pump (protons out of the cell), HCO3-/Na+ (bicarbonate entry) and Na+ dependent uptake of conjugated bile salts or bile acids.

 

***Bile salts are the most abundant solutes in bile

***Bile salts are the most abundant solutes in bile

***Transport from plasma into hepatocytes is mediated by the sodium taurocholate cotransporter.  

***Transport from plasma into hepatocytes is mediated by the sodium taurocholate cotransporter.  

*Chloride is excreted by the chloride/bicarbonate anion exchanger and the cystic fibrosis transmembrane regulator (CFTR) (Cl- channel on the luminal surface of the bile duct epithelial cells).

*Chloride is excreted by the chloride/bicarbonate anion exchanger and the cystic fibrosis transmembrane regulator (CFTR) (Cl- channel on the luminal surface of the bile duct epithelial cells).

[[Category:Liver and Gall Bladder - Anatomy & Physiology]]

[[Category:Liver and Gall Bladder - Anatomy & Physiology]]

[[Category:To Do - A&P]]

[[Category:To Do - ChrisB]]