The blood is a body tissue and is liquid in form. It consists of cells floating in the liquid medium. Blood cells are called corpuscles and liquid medium is blood plasma.
It is a complex fluid and it is about 55% of the blood, plasma consists of 90% water. It also contains proteins (albumins, Cogens).
Corpuscles-The blood cells are of three types :
Red Blood Cells (R.B.C.) or Erythrocytes–
The red blood cells are 5 million / cubic millimeter of blood in man. It is biconcave in structure. It is manufactured in the Red Bone Marrow and has a life of 20-120 days. Their main constituent is a red pigment called haemoglobin. Haemoglobin is a protein with iron in its molecule; Haemoglobin transports oxygen and carbon dioxide and the blooc appears red due to its presence.
White Blood Cells (W.B.C.) or Leucocytes-
The white blood cells are large and consists of one nucleus each. The number of W.B.C. is 8000 in per cubic millimeter. The W.B.C. are manufactured in Red Bone Marrow and has life period of 24-30 hours. These cells destroy the harmful bacteria and dead cells. These cells are the defense forces of the body against infection and injury, i.e. to provide the immunity to the body.
Blood Platelets or Thrombocytes–
These are small spherical bodied cells with nucleus. These cells help in clotting of blood, preventing the excess loss of the valuable blood.