liver physiology

• Liver


  • Largest gland of the body, weighing about 1.4 kg in an average adult
  • Located below the diaphragm, on the right side of the body
  • Main function is secretion of bile

  
• Hepatobiliary system


  Includes the liver, gallbladder and bile ducts

  
• Liver lobule


  • Six-sided structure (hexagon) that consists of multiple plates of hepatocytes arranged around a central vein
  • At each corner, there is a portal space which contains branches of bile duct, portal vein, and hepatic artery

  
• Hepatic plate


  • Contains bile canaliculus that accumulates bile from the hepatocytes and drains it into the bile duct
  • Contains sinusoid vessel that receives blood from the portal vein and the hepatic artery, and drains the blood into the central vein

  
• The direction of bile flow in the canaliculus (from center towards the periphery) is opposite to the direction of blood flow in the sinusoid (from periphery to the center)

  
• Liver sinusoids


  • Wide, highly permeable capillaries that contain a mixture of venous blood from the portal vein and the arterial blood from the hepatic artery
  • Wall is made of fenestrated endothelial cells, without a basement membrane
  • Hepatocytes are separated from the sinusoids by the space of Disse which contains loose connective tissue
  • Kupffer cells reside in the lumen of sinusoids and act as macrophages that kill bacteria through phagocytosis

  
• Blood supply of the liver

  • Receives blood from two sources - the hepatic artery (oxygenated blood) and the portal vein (venous blood containing newly absorbed nutrients, drugs, and possibly microbes and toxins from GIT)
  • Serves as a filter that can remove potentially harmful substances before they get into the systemic circulation
• Functions of the liver

  • Secretion of bile for fat digestion
  • Detoxication of blood
  • Synthesis of plasma proteins and clotting factors
  • Storage of blood
  • Metabolism of carbohydrates
  • Metabolism of lipids