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Blood Basics

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Blood Basics

Rakesh Mohan Hallen

BLOOD is invariably an emotive issue. Sight of blood is often linked to danger, as excessive bleeding can indeed lead to death. But in the accident and disease prone society we live in, it is unfortunate that awareness about blood is most often inadequate. The information transacted during normal curricular education is seldom sufficient. For example, do you know:

* What is the difference between animal and human blood?

* What happens to blood when a person dies?

* Why is the blood red?

* Why is blood thicker than water?

* In our blood we have both WBC; RBC, then why is it that when we get a cut only red blood flows?

* If the gravitational force of earth increases or decreases, will it affect our blood circulation?

* Why does the blood pressure change(increases/decreases)when there in a change is the gravitational force?

* Is it possible to transfuse blood of other animals to human beings?

* Do ants have any blood?

* Why don't insects bleed?

In order to answer such queries it is necessary to get familiarized with some details about blood.

The flow of blood in our body and the transport system in a metropolis are perhaps analogous. A living body needs a transport system just like a metropolis needs it to carry its cargoes to and fro. In the vast complex of the body of a living being blood carries out this function. But compared to the ceaseless flow of blood in our body, the teeming traffic of the busiest metropolis would appear a trickle. For the normal functioning of our body loading and unloading goes on day and night at every one of the body's billion cells. Food and oxygen are taken on; ammunition against attack from foreign bodies supplied, and waste products taken off.

Blood is a suspension of free cells: red blood corpuscles (erythrocytes or RBC), white blood corpuscles (leucocytes or WBC)and platelets (thrombocytes) in a fluid, known as the plasma. The plasma is composed of proteins (like globulins, albumin etc.), inorganic salts (e.g. the chlorides, bicarbonates and phosphates of sodium, potassium etc.), non protein organic substances (such as urea, glucose, cholesterol etc.) and water. One microlitre of human blood normally contains: 40 to 60 lakh RBC, 5 to 10 thousand WBC and 1.5 to 5 lakh platelets.

Now let's try the answers. Almost all vertebrates and invertebrates have blood of some kind. Blood of most animals is red in colour because one of the major constituent of red blood cells is a chemical compound, known as hemoglobin, which is a red pigment.

Just as the structure and function of the body of one organism differs from that of another organism so does their blood. This difference lies in the relative proportions of the constituents of plasma as well as in the nature of the corpuscular components. Also there are differences in human hemoglobin and hemoglobin of any other animal. The hemoglobin molecule of many mammals (which includes humans) is made up of four long chains of amino acids known as polypeptides or proteins. Each chain has an ion of iron at the center of its folded structure that can bind to an oxygen molecule. Although the order in which various amino acids in the polypeptide chains of hemoglobin occur in human blood is quite similar to the sequence in the blood of many other animals it is not exactly the same. There are indeed some differences between the amino acid sequence of human hemoglobin and the sequence in hemoglobin of most other mammals. Similarly, there are differences in the composition of white blood cells too. It is therefore not safe to transfuse the blood of other animals into a human body.

The iron containing hemoglobin which gives the blood of mammals the characteristic red colour is not universally present in the blood of all living organisms. For example in the blood of a grasshopper there is no oxygen carrying pigment. Similarly, the blood of mollusks (squids, octopuses and certain snails) contain hemocyanin, a colourless protein which turns blue in combination with oxygen. It is a copper compound unlike hemoglobin and hemerythrin which are iron compounds. Thus, even when an insect bleeds it may not be construed as bleeding only because its blood is not red.

As blood contains many inorganic/organic substance as well as corpuscles dispersed in water, it is more viscous than water and hence appears thicker.

The circulation of blood in most animals is due to the beating of heart. The heart acts like a pump in a close circuit. Gravity is indeed one of the factors which determine the flow of blood being pumped by the heart. If the gravitational force increases the flow will slow down which in turn will be reflected in the blood pressure.

When a person dies, his/her heart stops functioning. As a result the circulation of blood in the body stops. Thus blood cannot upload oxygen from the lungs. The deficiency of oxygen results in the cessation of many biochemical processes in the cells, which results in the blood becoming increasingly contaminated.


* Why blood group O can be given to other person having either of A, B, or AB blood group?

* If husband and wife both are having `Rh' positive blood groups, then what would be the Rh factor of their offspring?

* Who discovered the human blood groups?

* When the child is in mother's womb, is his blood group same as that of the mother or different? If it is different how would the child remain alive?

* Why does not everybody have the same blood group?

* What is Rh+ and Rh- in human blood? How does it affect the second born child?

* Why should a man with Rh+ blood group not marry a woman whose blood group is Rh-?

* Why does the blood group of two children of same parents differ?

* Do animals also have blood groups like humans?

* When a mosquito bites different persons different types of blood groups get mixed within its body. Then, how does it survives?

* If a louse feeds on the



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