Functions of the Liver

The liver is the body's largest compound gland. It is a major metabolic organ, and is important for degrading alcohol and drugs. It stores glycogen, secretes glucose, plasma proteins and lipoproteins into the blood, and secretes bilirubin (by-produce of haemoglobin), secretory IgA, and bile salts (which emulsify fats) as components of bile (endocrine secretion of the liver).

It is unusual because it has a dual blood supply. Not only does it receive arterial blood from the hepatic artery (about half of the total blood flow), it also receives blood from the hepatic portal vein, which contains nutrients absorbed from the GI tract. After passing through the liver, the blood collects and leaves in hepatic veins. These major blood vessels, enter and leave the liver at the porta hepatis. Also emerging from the porta hepatis are the left and right hepatic ducts which contain the collected bile, and the efferent lymphatics.

This shows a section through a pig liver, which has clear liver lobules. Can you identify lobules, the central vein, supporting connective tissue and portal tracts.

The liver has a thin capsule of dense connective tissue, and a visceral (inferior) layer of peritoneal mesothelium, and is divided into left and right lobes.

This is a section through a rabbit liver, which is more like that of a human liver. The lobules are far less obvious, but try to identify them, together with portal veins and portal tracts.

In this section of rabbit liver, the lobules are not defined by a layer of connective tissue, as found for the pig. This arrangement is more typical for most mammals, including man. However, lobular structure still present.

Can you identify the portal tracts and central veins.

The liver has very little connective tissue, which explains its softness, and susceptibility to tearing in abdominal trauma. however, a fine network of connective tissue fibres supports the hepatocytes and sinusoid lining cells.

Look at this picture, in which the network of fibres has been stained histochemically.

This shows the central hepatic vein, and the supporting reticulin fibres, which are made of type III collagen.

Now see if you can determine what's wrong with this section of liver.