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  The Mammalian liver, Biology tutorial

Introduction:

The liver is a big reddish-brown organ that lies on the right side of the body just beneath the diaphragm, partially overlapping the stomach. It is around 3 to 4 percent of net body weight. Blood supply to the liver is outstanding and it is the metabolic centre of the body. The liver performs quite a few functions comprising homeostasis. It screens the food present in the blood that is transported from the small intestine; it adjusts its content to please the instant requirement of the body, before discharging it into the circulatory system. Despite of the functions of the liver, there are numerous diseases related with it.

The Mammalian liver:

The liver is basically a reddish-brown organ that partially covers the stomach. The cells of the liver secret an alkaline greenish fluid termed as bile that is stored in the gall bladder, joined to the right lobe of the liver. The bile accumulated in the gall bladder is passed into the duodenum (for the emulsification of fat) via the bile duct.

The supply of blood to the liver is via two main blood vessels:

a) The hepatic artery that brings oxygenated blood from the dorsal aorta.

b) The hepatic portal vein that carry blood from the gut.

The liver distributes products all the way through veins. Their main function is to carry out by liver cells, which encompass numerous mitochondria and prominent Golgi apparatus. Microscopic inspection of the liver exhibits a close relation among liver cells, blood vessels and bile channels. It comprises lobules that are roughly hexagonal in shape; each and every lobule is filled with liver cells arranged in rows radiating from the centre in the direction of the periphery. On the sides of lobules are the branches of hepatic artery, portal vein and bile duct. The branches of the hepatic and portal veins are termed as interlobular blood vessels.

Functions of the Liver:

1) Regulation of Sugar:

Via the agency of insulin, the liver eliminates or adds up glucose to the blood. In the liver cell glucose is transformed to glycogen for storage or broken down to generate CO2, water and energy. Surplus glucose is transformed to lipids.

2) Regulation of Lipids:

The liver cells eliminate lipids from the blood and either breaks them down or modifies them and sends them to the fat depots.

3) Regulation of Amino acids:

The body doesn't store surplus protein or amino acids; surplus is destroyed by the liver in a procedure termed as deamination. In the procedure, the amino (NH2) group is eliminated and ammonia is formed. This is extremely toxic in small concentrations so it enters into reactions termed ornithine cycle in which it reacts with CO2 to make urea. This is at last eliminated from the blood by the kidneys.

4) Heat Production:

Because of many reactions occurring in the liver, much heat is generated. The liver thus regulates body temperature through its blood network conveying heat to other portions of the body

5) Bile Production:

Liver cells generate bile through the destruction of red blood cells; it is stored in the gall bladder. Bile is conveyed via the bile duct to the duodenum. Bile salts play a significant role in the emulsification of fat.

6) Cholesterol regulation:

It is a fat derivative of cell membranes particularly nerve cells. Surplus is excreted in bile and thus, crystallizes as the gall stones. The bile duct is blocked through bile stones leading to obstructive jaundice and skin becomes pale due to bilirubin accumulation in the blood. Surplus in blood blocks arteries leading to intra-vascular clot. When it takes place in the coronary vessels it leads to coronary thrombosis or heart-attack. Cholesterol elimination thus, is a significant function of the liver.

7) Removal of Sex Hormones:

The liver transforms sex hormones into other substances that are later eliminated through the kidney in renal excretion or via bile.

8) Red Blood Cell development:

The Red blood cells of fetus are generated by the liver. In adults, the liver generates Haematinic principle required for the making of the blood cells in the bone marrow. The liver generates the principle beneath the agency of vitamin B-12. Lack of principle leads to the pernicious anemia differentiated through reduced hemoglobin level.

9) Blood Storage:

As veins in the liver encompass a high power of expansion, they store blood around 1500 cm3, the liver, thus, acts as a reservoir for the blood.

10) Plasma Protein Formation:

The liver manufactures plasma protein comprising albumin, fibrinogen and globulin.

11) Detoxification:

This comprises conversion of foreign substances into harmless forms like substances which might be alcohol, drugs, food addictives and atmospheric pollutants. By all such functions, the liver regulates both the physical-chemical conditions of the internal atmosphere.

It is thus, a homeostatic organ.

A few Diseases of the Liver:

i) Jaundice:  This disease is caused by a raise in the blood bilirubin level, leading to the paleness of the skin and whitening of eyes. Jaundice is mainly due to three reasons.

  • Breakdown of big number of red blood cells that leads to the making of huge amount of bilirubin. This might take place throughout a malarial bout (particularly in new born babies) and in the disease termed as sickle-cell anemia (that is inherited defects of the red blood cells).
  • Blocking of the bile ducts through gall stones. The stones prevent the bile from emptying into the intestines, therefore leading to rise in blood level of bilirubin.
  • Harm of the liver cells decreases their capability to extract bilirubin from blood to form the bile. This increases the blood bilirubin level.

ii) Call Stones:  These are made in the gall bladder or bile ducts and are formed be cholesterol. Gall stones block the flow of bile and raise infections of the gall bladder, bile ducts and liver. It leads to swelling of the gall bladder.

iii) Viral Hepatitis:  It causes swelling and annihilation of liver cells. Viral hepatitis is caused by two kinds of viruses by (a) an infective hepatitis caused by virus type A and (b) scrum hepatitis caused by the virus type B.

iv) Amoebic liver abscess:  This is mainly cause by a parasitic amoeba termed as Entanweba histolitiect that as well causes dysentery. This parasite attacks the liver from big intestine via the hepatic portal vein. The parasite generates an enzyme which damages liver tissues and causes the formation of an abscess.

v) Cirrhosis:

In this situation, the damaged liver cells are substituted by futile fibrous tissue that makes the liver to firm and irregular. This disease is related by excessive utilization of alcohol over a long period and through hepatitis.

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