Stem cells in the bone marrow by a series of divisions form blood cells. The red blood corpuscles (RBCs) takes around five days to form from stem cells. It requires nutrients, including iron, amino acid, vitamin B12, and folic acid. A hormone called erythropoietin produced by kidneys determine the rate of RBCs are created. New cells released into the bloodstream from bone marrow are called reticulocyte. They developed into mature RBCs in about four days.
Red blood cells make up 40% of of a persons blood. White blood cells and platelets make up less than 5% of blood volume. The red blood corpuscles (RBCs) or erythrocyte carry oxygen from the lungs to body tissues. The oxygen is exchanged for carbon dioxide.
One cubic millimeter of blood contains around 5 million doughnut-shaped RBCs that are about 7.3 thousandths of a millimeter in diameter. They are much thicker around the edges than the center. The cell has a shape that assists it in absorbing and releasing oxygen molecules. The shape also allows the cell to squeeze through narrow vessels.
A protein hemoglobin that contains iron and is highly efficient at combining chemically with oxygen in the lungs and releasing the oxygen in the tissues is present in RBCs. When oxygen combines with hemoglobin oxyhemoglobin is formed. This is responsible for the bright red color and the oxygen free hemoglobin has a much darker color.
The enzymes, minerals,and sugars in RBCs gives energy to maintain shape, elasticity, and structure. The structure of RBCs varies so it can be classified into groups.
A life span of a RBC is around 120 days. As RBCs age their internal machinery wears out, they lose elasticity and become trapped in small blood vessels or organs where they are destroyed by a type of white blood cell called macrophage. Most of their components are reused but some are broken down into waste called bilirubin.
Abnormalities in the rate of creation or destruction of RBCs (as well as in the shape, size,and hemoglobin content) causes various forms of anemia and polycythemia.
White blood cells called WBCs or leukocyte. Their function is to protect the body from infection and fight infection when it occurs. WBCs are larger than RBCs. There are less WBCs in the blood than RBCs around 7500 per cubic millimeter. There are three WBCs they are granulocytes, lymphocytes, and monocyte.
The granulocytes which are responsible for isolating and killing invading bacteria. The granulocytes called neutrophils swallow bacteria earning them the name engulfing cells. The neutrophils live in blood for 6-9 hours then move through blood vessel walls into tissues where they survive a few days. The granulocytes called eosinophilis help in allergic reactions and parasitic infections.
The monocyte live 6-9 days and play an important role in immune system. The lymphocytes many formed in lymph glands rather than bone marrow. They play a central role in the immune system. T-type lymphocytes produce substances called lymphokines which effect the function of many cells. The T-type cells also moderate the activity of other B-type cells. These protects us from second attacks of diseases. These lymphocytes survive from three months to 10 years.
The leukemias a disorder of the number and maturity of WBCs . In Aids the T-lymphocytes are infected by a virus that causes a miss function an increases risk of infection and cancer.
Platelets are the smallest type of cells in the blood. There are more platelets than WBCs but less than the RBCs. They also are created in the bone marrow. They have a life span of about nine days. They adhere together in hemostasis (the arrest of bleeding) and in blood clotting. Because they form clots, platelets are known as thrombocyte. Abnormal platelets or lack of platelets lead to some bleeding disorders.