Surrounded by a serous and fibrous capsule or coat, the liver is made up of liver lobules (the functional units of liver). Each lobule is constructed around a central vein that empties into the right and left hepatic veins which then drain into the vena cava. The serous coat is derived from the peritoneum, and is present on the greater part of the organ surface. The fibrous capsule lies beneath the serous coat, and covers the entire surface of the organ.
The lobules form the chief mass of the hepatic substance; in humans, their outlines are very irregular. The bases of the lobules are clustered around the smallest radicles (sublobular) of the hepatic veins, to which each is connected by means of a small branch which originates from the center of the lobule (intralobular). The remaining part of the surface of each lobule is imperfectly isolated from the surrounding lobules by a thin stratum of areolar tissue, in which a plexus of vessels, interlobular plexus, and ducts are present.
Each lobule consists of a mass of cells known as hepatic cells, arranged in irregular radiating columns between which blood channels called sinusoids are present. The hepatic cells are polyhedral in form. They vary in size from 12 to 25μm in diameter. The cells usually contain granules; some of which are protoplasmic, while others consist of glycogen, fat, or an iron compound.
The liver receives blood supply from the hepatic portal vein and hepatic arteries. Supplying approximately 75%of the liver’s blood supply, the hepatic portal vein carries venous blood drained from the spleen, gastrointestinal tract, and its associated organs. The hepatic arteries supply arterial blood to the liver accounting for the remainder of its blood flow. Oxygen is provided from both the sources. Blood flows through the sinusoids and empties into the central vein of each lobule. The central veins coalesce into hepatic veins, which leave the liver and empty into the inferior vena cava.