ABSTRACT
The blood consists of a cellular component and a non-cellular matrix or plasma. Human blood is red in colour due to the iron in haemoglobin. The red blood cells settle at the bottom of the test tube since they are the heaviest. A small band of white blood cells can be identified above the red blood cells and the straw-coloured plasma remains on top since it is lightest. The plasma protein is fibrinogen which accounts for about 4% of the total. It is produced by the liver and is important for blood clotting. All blood cells are produced in the red bone marrow by a process known as haemopoiesis. Haemocytoblast produces two types of stem cells called myeloid stem cells and lymphoid stem cells. Myeloid stem cells differentiate into non-self-renewing precursor cells that eventually produce erythrocytes, thrombocytes and a number of leukocytes that have granules in their cytoplasm. Lymphoid stem cells produce non-self-renewing.
