Lec 31 - Liver

• All the soluble nutrients from the intestines will enter the venous side to the portal vein to the liver
• Majority of the blood supply to the liver comes from the intestines (nutrient rich but oxygen poor) and the other blood supply comes from the hepatic artery to supply oxygenated blood
• The functional unit of the liver are hepatocytes
• Hepatocytes

  • 6 sized cube shape
  • 2 sides are always in contact with a sinusoid
  • central nucleus
  • lots of euchromatin
  • moth-eaten appearance from glycogen
• Label the following slide

  A) hepatocyte

  B) endothelial cell

  C) sinusoids

  
• Sinusoids are lined by endothelial cells
• Major functions of hepatocytes

  Endocrine function - synthesis and secretion of:

  • proteins (albumin, prothrombin, fibrinogen)
  • cholesterol
  • lipoproteins

  Exocrine function - bile formation and secretion:

  • synthesis and recycling of bile acids

  Metabolism and storage

  • lipid soluble drugs
  • steroids
  • storage of carbohydrates as glycogen - maintain blood-glucose levels
  • detoxification - first pass metabolism
• Bile acids/salts aid in the breakdown of fat for absorption
• Venous portal system blood flow

  • mesenteric arteries to intestines
  • intestinal capillary bed
  • portal vein
  • hepatic sinusoids
  • hepatic vein
  • vena cava
• Portal vein blood enters the sinusoid to a central vein in the hepatic lobule then out towards the hepatic vein towards the vena cava
• Hepatic lobule has a hexagonal shape and at every point there is a portal triad
• There are blind-ended pouches from lymphatic vessels in some of the portal triads but not all of them
• The portal triad is made up of a portal venule, hepatic arteriole, and a bile duct
• Label this hepatic lobule

  A) central vein

  B) portal triad

  
• Between the walls of two hepatocytes is the bile canaliculus. This allows for the bile to travel away and out of the hepatocytes
• Label the components of the portal triad

  A) portal venule

  B) bile duct

  C) hepatic arteriole

  
• The space of disse is a space between a hepatocyte and a sinusoid where the hepatocyte will secrete into
• Sinusoids are made up of very fenestrated endothelium
• What is the black arrow pointing to?

  A) space of disse

  
• On the apical surfaces of the hepatocyte are the bile canaliculi
• The bile canaliculi is formed by two adjacent hepatocytes and two sets of tight junctions
• The basolateral surface of a hepatocyte are the sides that are in contact with sinusoids. The surface of the hepatocyte will have a ruffled appearance to increase surface area when secreting into the sinusoid (space of disse)
• Label this hepatocyte

  A) reticular fibers

  B) space of disse

  C) sinusoid lumen

  
• The ruffles on the basolateral side of a hepatocyte is made up of type III collagen (reticular fibers) to help maintain structure
• Glycogen can move bidirectionally between the cytoplasm and the liver. Can store or secrete it
• After the spleen starts the breakdown of old RBCs, they still need to be broken down further. That is done in the lvier by the hepatocytes. Liver macrophages (Kupffer cells) will eat the RBCs
• Label what the arrows are pointing to

  A) bile canaliculi

  
• One of the main products that is created when breaking down RBCs is bilirubin. Bilirubin is toxic and a buildup will cause jaundice.

  Once released by Kupffer cells, bilirubin is transported into the hepatocytes and from there is conjugated with glucuronide (makes it non-toxic) and then it is a waste product excreted out of the bile canaliculi
• Hepatocyte exocrine function is the creation and excretion of bile salts/acids. 90% are reused/recirculated dumped into the GI tract, reuptaken from liver, transported back into the bile canaliculi to be used again. 10% is de novo synthesis. They secrete bile through apical surface into bile canaliculi
• Label this slide from the liver

  A) hepatocyte

  B) bile duct

  
• The liver is constantly making bile acids at a steady production but the release is controlled by the gallbladder which stores the bile
• After the going through the bile canaliculi, the bile is collected into bile ductiles to be collected through the left and right hepatic ducts. They will merge and form the common hepatic duct. The duct from the gallbladder is called the cystic duct. These will all merge to form the common bile duct which dumps bile into the duodenum