LIVER

The liver is the largest gland in the body. It is dark-red, spongy and lobed.

The lobes are: caudate lobe, left lobe, right lobe and median lobe. It is hung from the posterior surface of the diaphragm by a ligament and partly overlaps the stomach. Underside of the right lobe is a gall bladder containing liquid called bile. Attached to the gall bladder is a bile duct which leads from the liver to the duodenum. Blood is supplied to the liver by the hepatic artery and hepatic portal vein. Hepatic vein carries blood away from the liver.

 

Bile

Bile is an alkaline greenish fluid with a pH of 7 to 8 secreted by the cells of the liver and stored in the gall bladder. It is passed to the duodenum through a bile duct. Bile has no digestive enzyme but performs the following functions:

1. It neutralises the acid chyme (food leaving the stomach) from the stomach. Bile has a pH of between 7 to 8. This is the best medium for the pancreatic enzymes to work.
2. Bile emulsifies fats and oils causing them to break into tiny droplets. Lipase can then act on the oil and fat droplets changing then into fatty acids and glycerol.
3. It prevents putrefaction (decay) of the food in the small intestine.

 

Functions of the liver

1) Blood sugar constant

Glucose in the blood stream is maintained at a constant level called blood sugar constant as low levels of glucose would be injurious to tissues of certain organs such as the brain that cannot store glucose. Surplus glucose is converted by the liver cells into glycogen for storage under the control of insulin. When blood sugar level is low, the glycogen is converted to glucose in order to maintain a constant blood sugar level. The liver also converts fructose and galactose to glucose for use by the body.

 

2) Deamination of proteins

Surplus amino acids (those not needed for growth and repairs) are deaminated in the liver. The nitrogenous part, together with the nitrogenous wastes from the breakdown of protoplasm is formed into urea which passes into the blood stream for transport to the kidneys.

 

3) Manufacture of bile

The liver makes and secretes bile. This is not a digestive juice and also contains excretory pigments, formed from the haemoglobin of dead red blood corpuscles. Bile is stored in the gall bladder in man. Rat has no gall bladder.

 

4) It manufactures fibrinogen from amino acids for clotting of blood.

 

5) It produces heat which is distributed to all parts of the body by blood circulation thus regulating the body temperature.

 

6) Removal of cholesterol from the blood

The liver removes cholesterol from the blood. Excess cholesterol if not removed from the blood may be deposited in the blood vessels leading to heart attacks. Excess cholesterol may also be excreted into the bile and precipitates and forms stones in the bile duct or bladder.7. It prepares fats for utilization as a source of energy.

 

7) Stores vitamin B12.

 

8) Stores iron, resulting from the decomposition of haemoglobin of dead red blood cells.

 

9) It converts other sugars to glucose. Fructose and galactose are converted by liver cells to glucose since glucose is the most suitable to the tissues generally.

 

10) Detoxification

Organic toxins produced by bacteria in the large intestine are absorbed into the portal blood. The liver prevents these compounds from reaching toxic levels in the body. Some enzymes present in the liver cells convert the toxic products into non-toxic compounds which are later excreted by the kidneys. For example, hydrogen peroxide which is a byproduct of many metabolic processes, is split into water and oxygen by an enzyme called catalase in the liver.

 

11) Manufacture of foetal red blood

The liver of the embryo manufacture his or her red blood cells.

 

The effects of malfunctioning of the liver

1. Bile may not be produced. Therefore fats and oils will not be emulsified for digestion by lipase.
2. Excess sugar may not be converted into glycogen for storage. Therefore excess sugar will be in the blood than necessary.
3. Iron and vitamin B12 may not be stored.
4. Fibrinogen may not be manufactured for blood clotting.
5. The liver may fail to deaminate amino acids, therefore nitrogenous wastes may accumulate in the body causing harm.
6. The body temperature may fall as the liver may fail to produce heat for the body.
7. The toxic products produced by bacteria in the body may not be converted into non-toxic compounds. Therefore the toxic products will be harmful to the body.
8. In pregnant mammals, the embryos will be anaemic as the liver may not be able to form red blood cells for the embryos.