White blood cells can be mainly divided into two types.
Granulocytes or granules and Agranulocytes or agranulocytes

Granulocytes
White blood cells whose cytoplasm is granular are called granulocytes. The granules are stained with Leishman stain. Its nucleus is 2-7 segmented. 72% of white blood cells are granulocytes. Their lifespan is 4-8 hours. They arise from the myeloblast cells of the bone marrow. Based on the dye holding capacity and the structure of the nucleus, they can be divided into three groups.
1. Neutrophil
The cytoplasm of neutrophils is neutral in color and granular. They are spherical and the nucleus is 2-5 lobed. Their diameter is 12-15 µm. Their number is 4900 per cubic milliliter. That is the highest which is 70%. Lifespan 2-5 days. It is produced in red bone marrow. They exhibit amoeboid motility and enter the site of infection through pores in the cellular network. This process is called diapedesis. They destroy microbes by the process of phagocytosis.
Function of neutrophils
(i) They send chemical messages about microbes
(ii) Increases vascular permeability by secreting lipids
(iii) Swallows microbes by the process of phagocytosis
2. Eosinophil
Their cytoplasm is bluish and acidic and the granules stain reddish-orange with eosin dye. They are spherical and the nucleus is 2-3 lobed. Their diameter is 12-17 µm. Their number is 150-400 per cubic milliliter. That is 1.5% of white blood cells. Lifespan 8-12 days. It is produced in red bone marrow. They are more common in the alimentary canal.
Function of eosinophils
(i) They secrete larvicidal polypeptides and destroy worm larvae
(ii) It destroys allergic antibodies.
(iii) Swallows microbes by the process of phagocytosis
(iv) Secretes hydrolytic enzymes.
(iv) Schistosoma and Trichinella cause death of parasites.
3. Basophil
Their cytoplasm is alkaline and the granules are stained bluish-black. They are round, nucleus is kidney shaped and bilobed. Their diameter is 12-15 µm. Their number is 35 per cubic milliliter. That is the lowest which is 0.5%. Life expectancy is 12-15 days. It is produced in red bone marrow.
The function of basophils
(i) Dilates blood vessels by producing histamine.
(ii) Prevents blood clotting by producing heparin.

Agranulocytes
White blood cells whose cytoplasm lacks granules are called agranulocytes. Their nuclei are large, intact and transparent. 28% of white blood cells are agranulocytes. They originate from bone marrow and lymphoid tissue. They can be divided into two categories.
1. Lymphocytes
Lymphocytes are small in size, round and have large nuclei. It is alkaline and alkaline. Its diameter is 6-16 µm. Their number is 1680 per cubic milliliter. 24% of white blood cells are lymphocytes. Life expectancy is 7 days. It is produced from red bone marrow, liver, spleen and lymph glands. There are three types of lymphocytes.
(i) B-lymphocytes: B-lymphocytes are derived from thymocytes of the thymus gland.
(ii) T-lymphocytes: T-lymphocytes are derived from hematopoietic progenitor cells of bone marrow.
(iii) NK cells: NK cells are toxic to other cells and are detrimental to immunity.
Function of lymphocytes
(i) Produces antibodies and destroys germs
(ii) Acts as a memory cell
(iii) Attacks the virus directly
(iv) Destroys cancer cells.
2. Monocytes
Monocytes are the largest white blood cells. Its nucleus is kidney-shaped or horseshoe-shaped. Its diameter is 12-20 µm. Their number is 280 per cubic milliliter. 4% of white blood cells are monocytes. Lifespan 2-5 days. It originates from red bone marrow (monoblast cells), liver, spleen and lymph nodes. 30-40 hours after generation it transforms into macrophage.
The function of monocytes
(i) Acts as a natural drain
(ii) Ingests viruses and bacteria
(iii) causes phagocytosis.

Contains nucleoproteins, glycogen, lipids, cholesterol, ascorbic acid and proteolytic enzymes.

9,000-30,000 per cubic milliliter of blood in neonates; Children under two years of age have 6,200-17,000 white blood cells and adults 4,000-10,000. Its average number is 7,000. Its number is more in the body of children and sick people. The ratio of red and white blood cells is 600:1.

It originates from the bone marrow, spleen and lymph glands. The process of white blood cell production is called myelopoiesis.

1. It is colorless as it does not contain hemoglobin.
2. It is irregular and relatively large.
3. Its diameter is about 7.5-20.00 µm.
4. Its size may vary.
5. It is nucleated and the nucleus is located at one end.
6. Its nucleus is initially spherical, ovoid or circular and becomes ovoid with age
or horseshoe-shaped.
7. Its average lifespan is 1-15 days.
8. It exhibits amoeboid movement. In this way it reaches the infected area and destroys the germs.

The word leucocyte is formed from the Greek words leucos meaning colorless and kytos meaning cell. Colorless irregular nucleated cells of blood are called white blood cells. Lymphocytes and phagocytes are vigilant guards and fight against pathogens. Kapffer cells in the liver are a type of white blood cell. If the number of white blood cells is more than normal, it is called leukocytosis and if it is less, it is called leukopenia. When its number decreases, immunity decreases. If the number of white blood cells increases, cancer is called leukemia.

1. Oxygen transport: Red blood cells transport oxygen as oxyhemoglobin.
2. Carbon Dioxide: Red blood cells transport carbon dioxide as carbaminohemoglobin.
3. Bile production: Red blood cells change to produce bilirubin and biliverdin.
4. Viscosity: It maintains blood density and viscosity.
5. Maintain acid-base balance: Red blood cells maintain acid-base balance in the body.
6. Blood Grouping: It has plasma membrane antigen proteins which are responsible for blood grouping.
7. Nitric oxide production: Red blood cells produce nitric oxide. Nitric oxide is used in endothelial cells like L-arginine.
8. Constriction of blood vessels: Red blood cells produce hydrogen sulphide. Hydrogen sulfide signals the constriction of blood vessels.

Every cubic milliliter of blood contains 50-54 lakh red blood cells in the male body, 45-48 lakh in the female body, 60-70 lakh in the child’s body and 80-90 lakh in the fetus. These cells are more abundant during exercise and pregnancy.

Red blood cells are produced in the liver, spleen and thymus during the fetal stage. Produced from bone marrow (erythroblasts or stem cells and hemocytoblast cells) from birth to 20 years of age. It is called erythroblast because it has a nucleus when it is produced in the bone marrow. The rest of the life is formed from the ends of the humerus, femur, sternum, vertebrae, vertebrae etc. The human body produces 400-500 ml of red blood cells every month. Every second, 10 million red blood cells are produced and 10 million are destroyed. It is destroyed in the liver and spleen. The kidneys secrete the hormone erythropoietin. The hormone erythropoietin regulates the production (more or less) of red blood cells. The process of making red blood cells is called erythropoiesis.

1. It is red in color because it contains hemoglobin. 100 ml of blood contains 15-16 grams of hemoglobin. Each red blood cell contains 29 picograms of hemoglobin.
2. It is round, bi-concave and disk-like.
3. Its diameter is about 7.5 µm and thickness is 2.0-2.5 µm.
4. Its periphery is smooth and thick and the middle is thin. Center thickness is 1.0 µm.
5. Mammalian red blood cells do not have a nucleus (exception—camel).
6. Its average lifespan is 120 days or 4 months. During this time it covers a distance of 1100 km.
7. It contains 60-70% water and 30-40% solids (90% of the solids are hemoglobin).
8. It helps in making bilirubin and biliverdin.