Liver Anatomy

Unique regenerative capacity Ensures that the liver to body ratio is maintained at 100 % - described as the hepatostat Liver important to the metabolism of the human body Increases in size in pregnancy and decreases following severe body weight loss The hepatostat maintains the liver in proportion to body size and needs

Anatomically four lobes: left, right, caudate and quadrate Functionally considered as two lobes - left and right Diaphragmatic surface: superior upper surface of the liver Visceral surface: faces adjacent abdominal organs (faces downwards); the porta hepatis and gallbladder are located on this surface.

The Caudate lobe is next to the inferior vena cava

is next to the gall bladder

Falciform ligament: separates the major right and left lobes and attaches the liver to the diaphragm and anterior abdominal wall, secures the liver the anterior abdominal wall Round Ligament: Found at the lower edge of the falciform ligament Gall bladder – accessory organ – pear shaped sac 7-10 cm long Rests in a recess on the inferior, visceral surface of the liver

Hepatic portal vein delivers poorly oxygenated blood from the GI tract Hepatic artery delivers oxygenated blood from the heart Hepatic portal vein and hepatic artery divide into two to supply the left and right side of the liver

via the hepatic portal vein and hepatic artery

the hepatic artery to supply blood to the liver Well oxygenated blood

of the GI tract including spleen and pancreas. Nutrient rich but poorly oxygenated blood The sources of blood mix within the liver and then drain into the central vein which empties in to the Hepatic vein and ultimately into the inferior vena cava to return blood back to the heart

Diverse functions of the liver are performed by hepatocytes. Hepatocytes are 60 % of the cells found in the liver (and 80 % of the liver mass). Other cell found in the liver: Endothelial cells, stellate cells, biliary epithelial cells (cholangiocytes), Kupffer cells and other immune cells

The liver is formed of repeating anatomical units called hepatic lobules Blood flows in the hepatic lobules from the edge via portal trials Inward blood flow in the portal trials from the hepatic portal vein and the hepatic artery Blood flows through the hepatic lobule via sinusoidal vessels and then drains into the central vein The central vein empties into the hepatic veins and then to the inferior vena cava

Bile flows in the opposite direction through the liver lobule Bile flows down bile canaliculi towards the portal triad where it flows into bile ductules From the bile ductules it is transported towards the gastro-intestinal tract and gall bladder Blood flows from the portal triad to the central vein Bile flows in the opposite direction towards the portal triad

Hepatocytes are specialized polarized cells (one side of the cell looks different to the other side – asymmetry in structure) Hepatocytes separate sinusoidal blood from the canalicular bile Basolateral membrane faces the liver sinusoidal endothelial cells Apical membrane faces the bile canaliculi jointly with the directly opposing hepatocytes

Exocrine secretory product of the liver Bile contains HCO3-, cholesterol, lecithin (a phospholipid), bile pigments and bile salts Bile salts are important for the absorption of water insoluble fats Stored and concentrated in the gall bladder Released during meals

Counter current flow of blood and bile (opposite directions) Bile ducts lined by hepatocytes Blood sinusoid lined by single layer of fenestrated endothelial cells Portal field (portal triad) composed of portal hepatic vein, portal artery and bile duct Central vein drains to the vena cava

Filter between the lumen of the hepatic sinusoid and hepatocytes. Minimize any barrier for the bi-directional transfer of small or soluble substrates between blood and the extracellular space of Disse

80 – 90% tissue macrophages in the liver; also known as stellate macrophages Discovered by pathologist C von Kupffer Reside in the lumen of the sinusoids of the liver, adherent to endothelial cells Important role in host defence

Stellate cells are found in the subendothelial space between the basolateral surface of hepatocytes and anti-luminal side of the sinusoidal endothelial cells spindle-shaped cell bodies with oval or elongated nuclei single stellate cell usually surrounds more than two nearby sinusoids Thought to be involved in liver fibrosis

Bile is transported down bile canaliculi in the liver The bile canaliculi empty into bile ductules and then bile ducts Empties into the hepatic ducts Bile then directly enters the duodenum or diverted to the cystic duct into the gall bladder The gall bladder concentrates and stores bile ready for use

Pear shaped, 7 -10 cm long Fundus: wide end of gall bladder and projects from the inferior border of the liver Body: contacts the visceral surface of the liver Neck: narrow and tappered; makes an S bend into the cystic duct. Internally the mucosa spirals into the spiral fold that keeps the cystic duct open.

Cholangiocytes are epithelial cells that line the intra- and extra-hepatic ducts of the biliary tree Modifies bile to generate ductal bile Cystic Duct is approx 4 cm long The cystic duct connects the neck of the gall bladder to the common hepatic duct