ratio, hence oxygen diffuses quickly in and out of the cell. The RBCs are devoid of nucleus, mitochondria, ribosomes and endoplasmic reticulum. The absence of these organelles accommodates more haemoglobin thereby maximising the oxygen carrying capacity of the cell. The average life span of RBCs in a healthy individual is about days after which they are destroyed in the spleen (graveyard / cemetery of RBCs) and the iron component returns to the bone marrow XI Std Biology-Zoology Chapter- large sized and constricted into several lobes but not joined by delicate threads.
Basophils secrete substances such as heparin, serotonin and histamines. They are also involved in inflammatory reactions. Agranulocytes Agranulocytes are characterised by the absence of granules in the cytoplasm and are differentiated in the lymph glands and spleen. These are of two types, lymphocytes and monocytes .
Lymphocytes constitute % of WBCs. These have large round nucleus and small amount of cytoplasm. The two types of lymphocytes are B and T cells. Both B and T cells are responsible for the immune responses of the body.
B cells produce antibodies to neutralize the harmful effects of foreign substances and T cells are involved in cell mediated immunity. for reuse. Erythropoietin is a hormone secreted by the kidneys in response to low oxygen and helps in differentiation of stem cells of the bone marrow to erythrocytes (erythropoiesis) in adults. The ratio of red blood cells to blood plasma is expressed as Haematocrit (packed cell volume).
White Blood Cells White blood cells (leucocytes) are colourless, amoeboid, nucleated cells devoid of haemoglobin and other pigments. Approximately to per cubic mm of WBCs are seen in the blood of an average healthy individual. The different types of WBCs are shown in Figure . .
Depending on the presence or absence of granules, WBCs are divided into two types, granulocytes and agranulocytes . Granulocytes Granulocytes are characterised by the presence of granules in the cytoplasm and are differentiated in the bone marrow. The granulocytes include neutrophils, eosinophils and basophils . Neutrophils are also called heterophils or polymorphonuclear