Digestion Tract: Accessory Organs

Liver has a unique blood supply. It receives blood from the small intestine, pancreas, and spleen via the hepatic portal vein. This vein carries 75% of the blood supply to the liver, essentially depleted of oxygen. It contains nutrients, noxious materials, blood cells and breakdown products of blood cells (from the spleen), and endocrine secretions of the pancreas. The hepatic artery carries oxygenated blood to the liver, making up the remaining 25% of the supply. Blood from the hepatic portal vein and hepatic artery is mixed as it perfuses hepatocytes of the parenchyma. Hepatocytes are never exposed to fully oxygenated blood. In the liver parenchyma, branches of the hepatic portal vein and hepatic artery supply the sinusoidal capillaries (sinusoids). There is also draining of the branches of the bile ducts system. These three constitute and travel as the portal triad, because the portal triad involves the lymphatic vessels as well. The liver structure includes hepatocytes (plates of cells), connective tissue stroma (blood vessels, nerves, lymphatics, and bile ducts travel within the CT), sinusoidal capillaries (sinusoids [between plates of cells]), and perisinusoidal spaces (or spaces of Disse). There are three descriptions of liver lobules:

Blood Vessels of the Parenchyma:

Space of Disse associated cells. In addition to the lining endothelial cells, the space of Disse is associated with:

Hepatocytes are large polygonal cells with large central, spherical nuclei. Many cells are binucleate and tetraploid (have 4x amount of DNA). Each nucleus contains -12 well developed nucleoli. They have numerous mitochondria (800-1000/cell), several small Gogli complexes per cell, developed rER, and developed sER.

The biliary tree is a system of conduits of increasing diameter that carries bile from the hepatocytes to the gallbladder and intestine. The flow of bile is centrifugal (opposite the flow of blood), beginning at the region of the central vein and proceeding to the portal canal.