Human blood is a red-coloured fluid connective tissue. An average person contains about 6.5 litres of blood. Blood consists of two components- plasma and blood corpuscles or blood cells.
Plasma:
Plasma is the liquid part of the blood. It contains 90 percent water. The blood corpuscles float in the plasma.
Blood corpuscles:
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Blood corpuscles are of three types:
1. Red blood corpuscles (RBC):
Red blood cells are disc-shaped cells that contain a red-coloured pigment called hemoglobin. Haemoglobin combines with oxygen and transports it to all parts of the body. In a similar manner it collects CO2 from the tissues and transports it to lungs.
2. White blood corpuscles (WBC):
White blood cells are large irregularly shaped cells. They are much bigger than red blood cells and are fewer in number. WBC consume harmful bacteria and viruses that enter our body and produce special substances called antibodies that protect us from infection.
3. Platelets:
Platelets are smaller than the red blood cells and help in the clotting of blood. In case of an injury, the platelets from a blood clot along with some proteins from the plasma and prevent blood loss.
Blood transfusion:
Blood is a very vital component of the human body. In case of an injury, severe sickness or during operations, large quantity of blood may result in death. In such cases, blood from a healthy person called the donor is given to the sick person. The sick person who receives blood is called the recipient. The process of transferring blood from a healthy person (donor) to a person deficient in blood (recipient) is called transfusion. Great care has to be taken by the doctors while transfusing blood from the donor to the recipient.
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There are four types of blood groups in human beings- A, B, AB, and O. Different people have different blood groups. Blood of some groups does not match with some other groups. If blood groups that do not match with each other are mixed, the red blood cells would clump together leading to the death of the individual.
Hospitals have blood banks where blood can be temporarily stored before it is given to patients. Every healthy person must donate blood periodically to the blood banks so that it can be given to sick persons as and when the need arises.