Bile, Enterohepatic, and Portal Circulations (Week 2--Beaven) Flashcards
What does a portal triad contain?
1) Hepatic arteriole (25% of blood into liver)
2) Portal venule (75% of blood into liver)
3) Bile ductule
(4) Lymphatic vessels)
Blood and bile flow between portal triad and central vein
Blood flows from PT to central vein
Bile flows from central vein to PT
Zone 1, 2, 3 of the liver
Zone 1: around PT; highest O2, gluconeogenesis; viral hepatitis comes in through PT so starts here
Zone 2: combo between 1 and 3
Zone 3: around central vein; lowest O2, glycolysis, lipogenesis; fatty liver starts around central vein
Portal system
Capillary bed then veins then another capillary bed THEN to the heart
1) Hepatic portal system: capillary bed of gut (splanchnic capillaries) to portal vein into capillary/sinusoids of the liver to hepatic vein to inferior vena cava
2) Pituitary gland
What is the endothelium of the liver?
Fenestrated endothelium
So albumin can get access to/from hepatocytes
How much of the liver can we cut out?
In humans, cut 1/3 and over 2 to 3 months will grow back
Liver will fill the space its in (either grow or shrink)
What liver diseases occur in the hepatic artery (pre-sinusoidal)?
Portal vein thrombosis (blood clot; imbalance in clotting factors, or cancer)
Schistosomiasis (rare, parasitic infection that feeds off nutrients)
What liver diseases occur in the sinusoids?
Viral hepatitis (B and C are chronic)
Toxins, alcohol
Cholestatic
Fatty liver
Almost all else
What liver diseases occur in the hepatic vein (post-sinusoidal)?
Venoocclusive disease (complication of bone marrow transplant)
Budd Chiari (rare)
Inferior vena cava web (rare)
Heart failure (backflow to liver leads to portal HTN)
What happens when you get cirrhosis?
Shrunken, scarred liver (cirrhosis) –> increased blood pressure in portal vein (portal hypertension) –>
1) Esophageal and gastric varices (50% people die when this happens)
2) Paraumbilical varices (caput medusae)
3) Rectal (NOT hemorrhoids) and paracolic varices
4) Spleen enlarges (splenomegaly), and chews up/traps platelets too much (low platelet count)
What is the apical/canalicular membrane and what goes across this membrane?
2 hepatocytes form a bile canaliculus between them (blood and bile run perpendicularly)
Hepatocytes makes bile salts/acids and secretes them across this membrane
Cl/HCO3 channel to maintain electrical neutrality
Channels for cholesterol, conjugated bile acids, phospholipids (components of BILE!)
Channels for conjugated bilirubin, GSH, drugs/toxins
Flow of bile (Enterohepatic Circulation)
Phospholipids, cholesterol, conj bile acids secreted across apical/canalicular membrane into canaliculus –> thru liver through canals of Hering (liver turns bile acids into bile salts) –> bile salts out of liver into R/L then common hepatic duct, etc. where is modified by absorption/secretion –> gall bladder for concentration (5x)/storage –> through cyctic then common bile duct through sphincter of Oddi –> duodenum –> bile salts partially converted back to bile acids by gut bacteria –> bile salts and bile acids reabsorbed in terminal ileum –> portal vein back to liver
Note: bile acids need to bind to albumin in order to be transported in portal circulation
Portal circulation tied to biliary circulation via Enterohepatic Circulation
Which vitamins are at risk if you have disruption with terminal ileum and enterohepatic circulation?
Fat soluble vitamins: K, A, D, E
Water soluble: B12 (because absorbed at terminal ileum)
How could enterohepatic circulation be interrupted?
Resection (surgical)
Inflammation/edema (infection, IBD (Chron’s, Ulcerative Colitis), autoimmune)
Radiation
What is bile composed of?
67% bile salts
26% phospholipids (lecithin) and cholesterol
- 5% proteins
- 3% bilirubin