. Explain Liver and its Structure with suitable diagram
The liver (1.2 to 1.5 kg), the largest internal organ, is located in the upper right and central portions of the abdominal cavity, just below the diaphragm. It is reddish brown in colour and well supplied with blood vessels.
1. A fibrous capsule encloses the liver, and connective tissue divides the organ into a large right lobe and a smaller left lobe. The falciform ligament is a fold of visceral peritoneum that separates the lobes. The liver also has two minor lobes, the quadrate lobe near the gallbladder, and the caudate lobe close to the vena cava.
2. Each lobe is separated into many tiny hepatic lobules, which are the functional units of the gland. A lobule consists of many hepatic cells that radiate outward from a central vein. Each lobule is covered by a thin connective tissue sheath called the Glisson’s capsule. Vascular channels called hepatic sinusoids separate plate like groups of these cells from each other. Blood from the digestive tract, which is carried in the hepatic portal vein, brings newly absorbed nutrients into the sinusoids. At the same time, oxygenated blood from the hepatic artery mixes freely with the blood containing nutrients, then flows through the liver sinusoids and nourishes the hepatic cells.
3. Often blood in the portal veins contains some bacteria that have entered through the intestinal wall. However, large Kupffer cells, which are fixed to the inner lining (endothelium) of the hepatic sinusoids, remove most of the bacteria from the blood by phagocytosis. Then the blood passes into the central veins of the hepatic lobules and move out of the liver.
4. Within the liver lobules are many fine bile canals (or canaliculi), which receive secretions from the hepatic cells. The canals of neighboring lobules unite to form larger ducts, and then converge to become the hepatic ducts. These ducts merge, in turn, to form the common hepatic duct.