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Blood is the most important fluid in our body. An adult human body carries 5 liters of blood. It is about 6% of our weight.

The main function of supplying oxygen and food (nutrients) to our human cells is done by blood. Wastes like carbon dioxide, ammonia are collected and transported so that they are disposed off.

Human’s blood is categorized in to 8 groups: O+, O-, A+,A-,B+,B-,AB+ and AB-. Most common are the O+ and A+ blood groups.

Blood contains four main components: red cells, white cells, platelets and plasma.

Red cells (erythrocytes) are the larger microscopic cells without nuclei. Red cells constitute 40% of our blood. So blood appears red. Oxygen is supplied by red cells to all living tissues. They carry the carbon dioxide back. Red blood cells are produced in bone marrows. Haemoglobin is the protein molecule in a red cell.

White cells (Leukocytes) are about 1% of blood. These are also produced in bone marrows. Lymphocytes (white cells) respond to any call from the immune system of our body. They identify and bind to the alien proteins (virus or bacteria). Granulytes and macrophages (white cells) surround the alien protein and destroy it. These cells also remove dead cells and dust from blood.

Plasma is a solution (water) consisting of sugar, proteins, salt and fat. It contains minerals, enzymes, hormones, lipids, vitamins, and antibodies.  It appears clear yellow. It carries the other three cells across. Plasma is about 50% of blood. Plasma supplies nutrients to our cells and takes back the waste from metabolic activities.

Platelets (thromocytes) are cell fragments without nuclei. They form a protective layer at our wounds and stop the bleeding. They stimulate our immune system. These cells are also produced in bone marrows. 

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