In this article we will discuss about the Blood:- 1. Meaning of Blood 2. Functions of Blood 3. Normal Blood 4. Properties 5. Groups.

Contents:

  1. Meaning of Blood
  2. Functions of Blood
  3. Normal Blood
  4. Properties of Blood
  5. Blood Groups

1. Meaning of Blood:

Blood is a tissue consisting of different types of cells—the red blood cells (RBC), the white blood cells (WBC) and the platelets suspended in a liq­uid medium called plasma. It circulates in a closed system of blood vessels. The red colour of blood is due to hemoglobin present in the RBC.

2. Functions of Blood:

a. Blood transports oxygen from the lungs to the tissues and CO2 from the tissues to the lungs.

b. It transports absorbed food materials to the tissues.

c. It transports metabolic waste products to the kidneys, lungs, skin and intestines for removal.

d. In association with the kidneys and lungs it maintains the acid-base equilibrium of the body by its efficient buffering action.

e. It maintains the steady osmotic pressure in the tissues and fluids of the body being assisted by the kidneys and the skin.

f. The plasma proteins assist in the exchange of water in the body from the tissue to blood and vice versa.

g. It maintains the body temperature at a con­stant level during its circulation.

h. It transports hormones from the site of pro­duction to different tissues.

i. By clotting, it protects body from hemorr­hage.

j. The WBC form a defence against micro­organisms.

k. It transports metabolites from one tissue to another, e.g., lactic acid formed in mus­cle is transported to liver and so on.

l. Other substances in blood combat toxic agents; they are antitoxins, agglutinins, precipitins.

3. Normal Blood:

Blood Volume:

Males: 69 ml/kg body wt.

Females: 65 ml/kg body wt.

Plasma Volume:

Males: 39 ml/kg body wt.

Females: 40 ml/kg body wt.

Red blood cells (RBC): It is circular, non-nu- cleated bi-concave disc. The count of RBC in adult male is about 4.5-6.2 millions and in the adult fe­male is 4.0-5.5 millions per cu. mm. The life span is about 120 days. The formation and destruction of RBC are going on continuously.

Packed Cell Volume and Hematocrit Ratio:

The ratio is 45/55.

Hemoglobin:

In normal males and females, the hemoglobin contents of blood are 14.5-16.5 gm. and 12-14.5 gm. per 100 ml of blood respectively. One gram of hemoglobin can carry 1.34 ml oxygen under optimal conditions.

Components of Blood

Chemistry

Chemistry

4. Properties of Blood:

Specific Gravity:

The specific gravity of normal blood usually lies between 1.056 and 1.06. The specific gravity of plasma lies between 1.024 and 1.038 and roughly proportional to the protein content.

Viscosity:

The viscosity of blood is important in the sense that it determines the blood pressure. Human blood is 5 times as thick as water. The high viscosity is due to the cells, plasma has a very much lower viscosity. The viscosity of blood is affected by the change in the numbers or size of red cells or white cells. Abnormal values are found in leukemia’s, severe hemorrhage and pernicious anemia.

pH:

Blood is slightly alkaline and its pH lies between 7.35 and 7.45. In the resting individuals, the arterial blood is very slightly more alkaline (about 0.02) than venous blood.

This difference is increased by muscular exercise due to more forma­tion of lactic acid. Under normal conditions the pH of blood of an individual is maintained in the re­gion of 7.4. The pH of an individual is below 7.35 is considered in a condition of acidosis and over pH 7.45 is under the condition of alkalosis.

Osmotic Pressure:

Normally the osmotic pres­sure of blood is constant which is equal to 0.945% NaCl. The osmotic pressure of blood is slightly re­duced on the ingestion of large amounts of water and increased on strenuous exercise.

Clotting of Blood:

Blood is clotted or coagu­lated within 5 or 10 minutes after shedding if it is left undisturbed. Different factors are involved in blood clotting which is discussed elaborately in physiology.

Composition:

Sugar and urea are fairly equally distributed between plasma and corpuscles but oth­ers are almost entirely confined to one or the other, e.g., Na and Ca in the plasma and K in corpuscles. Bromide, iodide, indican, enzymes, anti-enzymes, hormones, vitamins and various antibodies are cir­culating in blood. Plasma contains 8% to 9% sol­ids, composed largely of proteins.

The constitu­ents of plasma are as follows:

In normal individuals, the plasma proteins vary from 6.0% to 8.5%.

The proteins are as follows:

Other proteins such as glycoproteins, lipopro­teins, enzymes and hormones are present in small amounts.

5. Blood Groups:

Human blood is classified into 4 main groups and several sub-groups. Agglutinogens are neutral ni­trogenous mucopolysaccharides with molecular weights ranging from 200,000 to 300,000. The four main groups are A, B, AB and O. The minor groups are M, N, P and Rh. The plasma contains antibodies called agglu­tinin. The distribution of agglutinogens in RBC and agglutinins in plasma in the four groups are noted.

To determine the blood group of an individual, an isotonic saline suspension of RBC is mixed with a test serum containing agglutinin α or agglutinin β on a slide. When no agglutination occurs, the cells separate and are evenly distributed. When agglutination occurs, the cells clump together.

The results are interpreted as follows:

1. Blood of group A is agglutinated by plasma of group B containing α-agglutinin.

2. Blood of group B is agglutinated by plasma of group A containing β-agglutinin.

3. Blood of group AB is agglutinated by the plasma of blood group A and B contain­ing agglutinins P and a, respectively.

4. Blood of group O is not agglutinated by the plasma of group A, B or AB. There­fore, persons of group O are called univer­sal donors. Anybody can receive their blood.

Rh Blood Groups:

It is an antigen of the Rhesus monkey and is present in the blood of 85% of white people and may be transmitted from father to child. The commonest Rh antigen is D and its antibody is anti D. If the mother is Rh negative, she develops antibodies to it and these antibodies pass through the placenta to the fetus and cause severe destruction of red blood cells in the new-born child.

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