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The Structure and Function of the Liver

External Structure

The liver is a soft, reddish brown, triangular organ with four lobes. A human liver weighs between 1.44 and 1.66 kg.

External Structure

The liver is supplied by the hepatic artery and the hepatic portal vein. The former branches of from carries blood from the aorta while the latter bring blood containing digested products from the small intestine.

Internal Structure

The liver is composed of numerous liver lobules which are cylindrical in shape. These lobules are the smallest functional units of the liver. They are made up of liver cells (hepatocytes) which are arranged in rows radiating from a central vein which branches off from the hepatic vein

Internal Structure

There are blood capillaries known as sinusoids which radiate from the central vein and run parallel to the radiating rows of hepatocytes. Also running parallel to the hepatocytes are intercellular spaces called canaliculi which contain bile from the bile duct.

Internal Structure

Oxygen rich blood from the hepatic artery and nutrient rich blood from the small intestine flow down the sinusoids towards the central vein.

Hepatocytes remove oxygen and nutrients from the blood and put in their waste products.

Internal structure

There are specialise phagocytic macrophages called Kupffer cells in the walls of the sinusoids which are responsible for removing bacteria and worn out red blood cells and destroying them. Hepatocytes are responsible for carrying out almost all of the functions of the liver.

Internal Structure

Hepatocytes have numerous mitochondria, granules of glycogen and large Golgi bodies. This is because they have a secretory function and they are involved in energy storage.

Internal Structure

In addition, hepatocytes have organelles known as peroxisomes which contain catalase. This plays an important role in the breakdown of ethanol which is derived form alcohol.

Functions of the Liver

The liver has many functions including the following:

Regulation of blood sugar levels, synthesis of non-essential amino acids, plasma proteins, foetal red blood cells, cholesterol, bile, control of lipid levels, storage of vitamins and minerals, generation of heat, breakdown of hormones, detoxification (deamination) and the destruction of old red blood cells

Functions of the Liver

Excess proteins cannot be stored in the body, Deamination takes place and this involves the removal of the amino group (NH2) from an amino acid resulting in the formation of ammonia.

Functions of the Liver

Ammonia is highly toxic. Consequently, the liver converts it into urea which is less toxic. The latter is then removed by the kidneys. (Ornithine cycle)

The liver breaks down other toxic substances such as hydrogen peroxide, toxins released by pathogens, alcohol and food additives