What is Blood? Blood Functions & Composition

What is Blood?

Blood is regarded as a modified liquid connective tissue because the cellular elements in it are separated by a considerable amount of liquid intracellular substance called plasma. The blood can be identified as the universal internal environment of the vertebrate body. It is an isotonic red viscous liquid and is heavier than water. (Sp. Gravity 1.050 to 1.060). Blood is slightly alkaline in nature having pH ramie from 7.3 to 7.5. In human beings, it is about 7% of the total body weight.

Functions of Blood

The blood circulating in the blood vessels has the following important functions.

1. Respiration– Blood carries oxygen from the respiratory surfaces to the tissues and carbon dioxide from the tissues to the respiratory surfaces.

2. Transport of nutrients– After the digestion of food in the gastrointestinal tract, blood carries the soluble food from the intestine to the tissue cells for utilisation. Moreover, the nutrients are mobilised from their stores and carried to the working organs according to the physiological requirement of the body.

3. Excretion– Due to the various metabolic processes different waste products are constantly produced by the body. These metabolic waste products and excessive salts and water are carried by the blood from the tissues to the sites of their elimination.

4. Communication system– Blood serves as a communication system in the body by transporting the secretions of endocrine glands, the hormones. The hormones are necessary for the regulation and coordination of the various activities of cells and tissues.

5. Maintenance of pH– The plasma proteins of blood act as a buffer system and maintain the pH of the blood.

6. Water balance– Blood is responsible for maintaining the water balance of the tissue fluid of the body.

7. Regulation of body temperature– The regulation of the body temperature is maintained by the blood and prevent a sudden change of body temperature. Blood transports heat from the deeper parts of the body to the surface where it can be lost.

8. Ionic balance– Blood maintains an ionic balance of the body.

9. Protective– The blood has a protective function and plays an important role in immunity. It protects the body against infection by producing antibodies. Moreover, the white blood corpuscles have phagocytic properties to engulf bacteria and foreign particles.

10. Prevents blood loss– Blood can prevent excessive loss of it in injury as it has the power of coagulation.

Composition of Blood

Blood is a highly complex fluid that is composed of two components

(i) Fluid component- The fluid component of the blood is called plasma.

(ii) Formed component- Cellular components of the blood which contains three types of cells namely red blood cells or erythrocytes (RBC), white blood cells or leukocytes (WBC) and thrombocytes or platelets.

If the blood is allowed to settle or centrifuged after adding an anticoagulant, two sharply contrasting layers will be formed. The upper clear colourless or yellowish layer in the blood plasma and the botton red coloured part is composed of erythrocytes and thrombocytes. The leucocytes are found on the surface of the bottom layer as a thin white film.

Plasma: The plasma is mainly the watery fluid part of the blood containing, different dissolved substances.

It forms about 55% of the total volume of blood in human. It has a specific gravity of 1.025 to 1.034. The plasma consists of 90-92 per cent of water and 8-10 per cent solids.

The inorganic constituents of blood plasma (0.9%) dissolved in water are the bicarbonates, phosphates, chlorides and sulphates of sodium, calcium, potassium and magnesium. Traces of iron. phosphorus and iodine are also present.

The organic constituent of plasma is about 8.1%. Serum protein or plasma proteins are the most important organic constituents of blood plasma.

Plasma protein: Total amount of plasma protein varies from 6.5 to 7.5 per cent. There are several types of plasma proteins differing in their properties and functions. The plasma protein is composed of different types of protein and they are (a) serum albumin — 4.7 to 5.7% (b) serum globulin — 1.3 to 2.5% and (c) fibrinogen0.2 to 0.4%. The serum albumin constitutes the major part of the total plasma protein and is responsible for the osmotic pressure of the blood. Serum globulin is the antibodies that provide immunity to various diseases. Fibrinogen is necessary for the coagulation of blood.

In addition to the above three important proteins, small amounts of prothrom bin, lipoprotein, glycoprotein have been isolated from the plasma by electrophoresis.

In addition to different plasmaproteins, certain other organic substances are also found in the plasma. These are- (1) Nutrients and catalysts. These are nitrogen free organic substances such as glucose, neutral fats and lipids, lactic acid, pyruvic acid, cholesterol. Moreover different enzymes, enzyme precursors, hormones are also present in the plasma.

Glucose is the main nutritive substance present in the plasma. It is absorbed by the blood from the intestinal villi. Some amount of glucose is stored in the liver in the form of glycogen. The glycogen also breaks down to glucose. Normally, a person gets 80-100 mg. glucose. per 100 ml of blood, in 12 hours after a standard meal. If the glucose level is regularly above 180 mg. per 100 ml of blood, it causes elimination of sugar along with the urine and then the condition is termed as glucosouria. The normal blood sugar level is maintained by the interaction of two hormones namely insulin and glucagon secreted by the endopancreas.

About 80-180 mg. of cholesterol is also present in 100 ml of blood in normal condition. The cholesterol is also absorbed by the blood from the intestinal villi and it is also synthesised by the villi. A diet containing more fat increases the cholesterol level in the blood. The cholesterol and the esters of cholesterol are not soluble in water and therefore it is normally deposited in the endothelial wall of the arteries and veins which may cause high blood pressure and abnormal heart function.

What is Blood? Functions & Composition

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