Lymphocytes are a type of white blood cells, which are responsible for protecting our body against bacterial and viral infections. They make up fifteen to forty percent of the total white blood cells that circulate in the blood stream. The two main types of lymphocytes are T cells and B cells, and both help to fight off infection and play a role in stopping the growth of cancers.

Fibrinogen is one of the important plasma proteins, which plays an important role in blood coagulation where it is converted by thrombin to fibrin. This is achieved through processes in the coagulation cascade that activates the zymogen prothrombin to the serine protease thrombin, which is responsible for converting fibrinogen into fibrin.

RBCs last an average of 120 days in the bloodstream. When RBCs get aged, they are removed by macrophages in the liver and spleen.

Blood group O individuals do not have either A or B antigens on the surface of their RBCs. But their blood serum contains IgM anti-A and anti-B antibodies against the A and B blood group antigens. Therefore, an individual of blood group O can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (i.e. A, B, O or AB). They are known as universal donors.

Progenitor cells are early descendants of stem cells that can differentiate to form one or more kinds of cells. After wounding, only stem cells contribute substantially to the repair and long-term regeneration of the tissue, whereas committed progenitor cells make a limited contribution.

This condition is called polycythemia.

These compounds are synthesised in normoblastic stage of developing red blood cells. Two molecules of succinyl CoA and two molecules of glycine combine to form a pyrolle ring. Four pyrolles combine together to form protoporphyrin IX. Protoporphyrin IX combines with iron and polypeptide chain to form haemoglobin chain. Four such haemoglobin chains make up haemoglobin molecule.

It is the passage of blood cells through the unruptured wall of a blood vessel into the surrounding tissues. The white cells may exhibit diapedesis to fight infection in the tissues surrounding blood vessels. The neutrophils are the first to arrive through diapedesis at the site of an infection.

Thymus is a small organ in the upper chest, under the breastbone. Before birth and during childhood, thymus helps the body to make a type of white blood cells. These cells protect our body from infections.

Basophils remain in blood for short duration, and later migrate to the tissues. Basophils liberate heparin, an anticoagulant substance, which produce allergic reactions. They also liberate small quantities of bradykinin and serotonin, which participate in inflammatory process.

It is the cancer of blood cells. The bone marrow starts to make a lot of abnormal WBC called leukemia cells, which grow faster than normal cells. Leukemia cells can crowd out the normal blood cells. This can lead to serious problems such as anaemia, bleeding and infections.

Colony Stimulating Factors (CSFs) are secreted glycoproteins that bind to receptor proteins on the surfaces of hematopoietic stem cells, and stimulate stem cells in bone marrow to form specialised white blood cells that defend the body against infection from viruses. It can also be produced by fibroblasts, macrophages and endothelial cells.

When we are exposed to a variety of harmful pathogens such as bacteria, viruses, fungi and parasites which can cause diseases, our body has a specific defence mechanism to protect our body from these pathogens. Leucocytes or white blood cells play a major role in body's defence mechanism. In leucocytes, neutrophils are considered the first line of defence against infection.

Estrogens have inhibitory effect on erythropoiesis through suppression of erythropoietin production. Estrogen is the main sex hormone in women, and is essential to the menstrual cycle.

Erythrocyte sedimentation rate is the rate at which red blood cells settle down. It is the measure of supernatant plasma separated out at the end of 1 hr when a column of blood mixed with an anticoagulant is kept undisturbed. ESR is increased in pregnancy and during menstruation, and also in infections like tuberculosis, rheumatoid arthritis, malignancy and anemia. ESR decreases in polycythemia and sickle cell anemia.