1: What is blood? how much blood does a person have?
Blood is the red coloured fluid flowing continuously in our body's circulatory system. about 1/12th of the body weight of a healthy individual is blood. on an average there are about 5 - 6 liters of blood present.
2: What is the composition of blood?
Blood contains mainly a fluid called plasma in which are suspended cellular elements. three types of cells - red blood cells or rbc's, white blood cells or wbc's and tiny platelets form the cellular element.
3: What are the functions of these components?
(a) plasma: acts as a vehicle to carry many substances like glucose, fats, and proteins, enzymes, and hormones etc., in addition to the blood cells.
(b) red cells: carry oxygen from lungs to various body tissues and take back carbon dioxide from the cells and tissues to be thrown out of body in the form of exhaled air.
(c) white cells: mainly act as body scavengers and guards. they help in the immune system of the body and act as defense forces of the body killing the bacteria or any other organisms entering the body.
(d) platelets: help in the clotting and coagulation of blood. we have experienced in our life that whenever we get injured the bleeding stops after a few minutes. this is brought about by a mechanism called clotting of blood in which platelets plays a very vital role.
4: How is blood formed?
blood consists of rbcs, wbcs, platelets suspended in plasma. in early embryonic life blood cells are formed in liver and spleen. but by the fifth month the haemopoisis (i.e., formation of blood.) occurs in bone marrow and lymphatic tissues. at birth the entire bone marrow is red and active. gradually as the child grows, the marrow remains red only in the flat bones and vertebrae. the rbc, granulocytes of wbc and platelets are produced mainly by bone marrow. the lymphocytes, monocytes, plasma cells are formed in the lymphoid and reticulo endothelial tissues. the orderly proliferation of the cells in the bone marrow and their release into circulation is carefully regulated according to the needs of body. every day, new blood cells are being produced in the bone marrow and every day old cells are dying and being removed from the body. red blood cells have a life of 120 days and when it becomes old and senile it is thrown out. white cells live for a few days and platelets for a few hours. thus daily new cells are added to the circulation and old are removed from it.
5: What are blood groups?
Every individual has two types of blood groups. the first is called the abo - grouping and the second type is called rh - grouping.
in the abo - group there are four categories namely a group, b group, o group and ab group.
in the rh - group either the individual is rh-positive, or rh-negative. rh is a factor called as rhesus factor that has come to us from rhesus monkeys.
thus each and very human being will fall in one of the following groups.
a positive or a negative
b positive or b negative
o positive or o negative
ab positive or ab negative
there are also some sub groups as well as a few other classifications.
6: What is the importance of knowing the blood groups?
for all practical and routine purposes, it is ideal to transfuse to the patient the same group of blood which he belongs to. it is only under very dire emergency that we take o group as universal donor and ab groups as universal recipient. under no circumstances o group can get any other blood except o. similarly a group patient cannot be given b group blood and vice versa.
7: Why the patient of 'a' group blood is not allowed to receive 'b' group blood?
This is due to the reason that, the blood of a group people contains anti - b antibodies. in b group people there are anti - an antibodies. if we give a group blood to a b group patient, it is bound to be incompatible and will result in serious consequences.
8: Why are rh negative and rh positive incompatible?
A patient with rh-negative blood cannot be given rh-positive blood as the antigen-antibody reactions will result in severe consequences.
in cases where a woman has rh negative and her husband has rh positive, the first child with rh positive may be normal. but subsequently the woman may not conceive or may have repeated abortions. there may be intra uterine fetal death. if the child born is alive, it will suffer from a fatal disease called "erythroblastosis foetalis". now mothers can be given an injection of anti-d within 24 hours of the delivery of a rh-positive child and thus protect the next baby from this catastrophe.
9: What is a unit of blood?
blood is collected in plastic bags which contain a watery fluid which prevents blood from getting coagulated. on an average we draw about 450 ml. of blood from a person, depending on the weight of the donor. this blood, plus the amount of anti coagulant present in the bottle or bag, is known as one unit of blood.
10: Can blood of animals be transfused to human beings?
Scientists have tried a lot but so far they are not successful. only the blood of a human being can be transfused to a human patient.