All you need to know about a liver.

The liver is the largest gland in the body and an important organ that has multiple functions it weighs approximately 3 lb and contains 300 billion cells. The liver lies in a sheltered position in the right side of the abdominal cavity beneath the diaphragm, where it is partly protected by the rib cage. The liver is intraperitoneally located, on one side it is linked with the lesser curvature of the stomach by the peritoneal folds, on the other side with the anterior abdominal wall by the crescent-shaped ligament. This ligament is connected to the round ligament of the Liver, which is remnant of uterine life. The liver is reddish brown in colour and consists of two lobes, the right and the left, both of which are made up of thousands of lobules.

The right lobe is about six times the size of the left, these lobes are wedge-shaped, smooth textured and feel rubbery. They contain hundreds of cells that resemble fine spokes, which multiply from the central vein, in a network of blood channels called sinusoids

Structural components of the liver include:
Hepatocytes: These are parenchyma cells that form plates they are the main functional cells of the liver.
Sinusoids: These are the wide vascular channels that separate the plates of hepatocytes. The majority of cells lining the sinusoids are endothelial cells however, scattered among these cells are specific macrophage type cells termed Kupffer cells these are part of the liver's defence system.
Bile ducts: These carry bile from the hepatocytes eventually into the duodenum. Bile is produced in hepatocytes and is secreted into a network of minute bile canaliculi (no discrete structure of their own) positioned between plasma membranes of adjacent hepatocytes. This network drains into small bile ducts, then into medium sized and large ducts and eventually into the common bile duct, which empties into the duodenum.
Portal tracts: These are islands of connective tissue containing branches of the portal vein and hepatic artery, running side by side, that bring blood to the sinusoids. They also contain bile ducts, which carry bile in the opposite direction to the blood flow

Figure 3: Architecture of the Liver Cells.

As the blood flows from the portal vein and hepatic artery it passes through the sinusoids where it is in intimate contact with the hepatocytes so it can exchange nutrients and metabolic products. The blood then flows into branches of the hepatic vein and finally into the inferior vena cava. The structural unit of the liver has traditionally been considered to be the hepatic lobule. It is now thought that the blood flow and function of the liver are more accurately defined by the unit structure known as the hepatic acinus. In the hepatic lobule concept, the lobule is roughly hexagonal in shape and is centered on a terminal hepatic venule. The portal tracts are positioned at the angles of the hexagon, blood from the portal vein and hepatic artery in the portal tract flow to the central vein

Figures 4/5: Illustration showing the architecture and blood supply of the liver.

The liver holds about 13 percent of the body's blood supply, which is supplied, by two distinct sources. A unique feature of the liver is that it has both arterial and venous blood supplies. Absorbed food products pass directly from the gut to the liver via the Hepatic portal vein. Oxygen required for liver metabolism is supplied through the Hepatic artery. Venous drainage occurs by way of the Hepatic vein.
Systemic circulation
Oxygenated blood flows in from the Hepatic Artery to the liver, which needs about a quarter of the hearts total output - 1.75 pints a minute. This subdivides into many branches within the liver to provide oxygen to all its cells. The hepatic artery normally comes off the celiac trunk.
Portal circulation
Nutrient-rich blood flows in from the Hepatic Portal vein, which also feeds the liver with blood, it carries nutrients from digested food such as fats and glucose from the intestines and spleen, which is stored, depending on the body's needs. The portal vein brings venous blood from the digestive tract, so that the liver can process the nutrients and toxins extracted from food. The hepatic veins drain directly into the inferior cava,