Liver Physiology

liver lobule

• basic functional unit of the liver

• constructed around a central vein, empties into the hepatic veins, theninto vena cava

• composed of liver cell plates that radiate from the central vein

hepatic plate

• two cells thick, and between the adjacent cells lie small bile canaliculi

• empty into bile ducts in the fibrous septa

portal triad

binds the lobule

• core of a portal lobule

classic hepatic lobule

drains blood from the portal vein and the hebatic artery to the hepatic or the central vein

portal lobule

drains bile from hepatocytes to the bile duct

portal acinus

supplies oxygenated blood to hepatocytes

• zone 3: least oxygenated

• Zone 2

• Zone 1: most oxygenated

role of hepatocytes in separating bile lumen from sinusoids

canaliculi form a pattern along the contiguous surfaces of hepatocytes and form a 3D tubular network

liver blood supply system

dual blood supply, but single venous drainage

• portal vein contributes ~75% of total circulation to the liver

• the hepatic artery contributes the other ~25%

• blood from sinusoids converges on terminal hepatic venules (central veins) which join to form the hepatic veins

role of hepatocytes

absorb blood nutrients and toxins, whilst expelling manufactured plasma proteins

• bile canaliculi run between rows of hepatocytes and pick up secreted bile and toxins

Kupffer cells

phagocytic, remove foreign matter that gets absorbed by the GI tract and delivered to the liver by the hepatic portal system

role of the hepatic portal vein

most of the blood flow to the liver arrives via this

• nutrient laden

• smaller volume of highly oxygenated blood arrives via the hepatic artery

blood exits via the hepatic veins on route to the heart

where does bile drain into?

drains into a single common duct before emptying into the duodenum

• the canaliculi into which bile is secreted form a three-dimensional polygonal meshwork of tubes between hepatocytes

• bile enters small terminal bile canals of Hering

• canals of Hering then empty into a system of perilobular ducts

the liver is a metabolic hub

• short term regulation of nutrient flux

• the liver stores and then releases nutrients for both catabolic and anabolic needs (“middle man”)

metabolism of glucose

gut-absorbed monosaccharides, largely glucose, are rapidly stored as glycogen for later use

• periods of fasting (glucose shortage): live ris a major site of gluconeogenesis

• also a site of fat metabolism to supply energy for gluconeogenesis

role of kupffer cells

defense: phagocytosis of bacteria

hepatic stellate cells

lipid storage: store a large portion of the body’s vitamin A

vascular (sinusoidal) endothelium

plasma-hepatocyte exchange (also house kupffer cells)

red blood cell breakdown process

• broken down and recycled by Kupffer cells

• hemoglobin —> globin and iron-containing heme groups

• globin borken down by peptidases to produce amino acids

• heme groups broken down into iron and bilirubin (bile pigment)

• iron is stored in the liver by ferritin

role of plasma proteins

hepatocytes make plasma proteins: albumin, globulins, fibrinogens, other

albumin function

major component of osmotic pressure of plasma

globulins

participate in the immune system (antibodies) and act as transport proteins

fibrinogen role

functions in blood clotting

function of bile

provides excretory route for solutes not excreted by the kidney

• secreted bile salts and acids are required for normal digestion and absorption

*recycled for repeated use

role of secretin/cholangiocytes

stimulates the cholangiocytes of ductules and ducts to secrete a watery, HCO3- rich fluid

• contribute to bile secretion

CCK/galbladder interaction during meals

• the gallbladder stores bile and delivers it to the duodenum during a meal

• CCK causes GB contraction and allows bile to promote fat digestion

• mucus secretion pretoects epithelium

bilirubin role

tool for diagnosing hemolytic blood diseases and liver disease

• jaundice develops when there is too much bilirubin in the blood

prehepatic jaundice

due to excessive destruction of RBCs

LDLs

major carriers of cholesterol in plasma

surplus cholesterol?

converted by the liver into bile salts, which can be eliminated via the bowels

• LDL (low density lipoprotein) transports cholesterol to cells for use in cell membrane and steroid synthesis

• HDL transports excess cholesterol from cells back to the liver (storage of conversion)