BLOOD CORPUSCLES (= BLOOD CELLS) -

Blood corpuscles are of the following three types: Erythrocytes, Leucocytes and Thrombocytes.

(A)     Erythrocytes (Red Blood Corpuscles or RBCs)

1. They are the most abundant cells in the human body.
2. A normal adult man and woman have 5 and 4.5 million RBCs per cubic millimetre of blood.
3. Low total count of RBCs leads to anaemia.
4. Matured mammalian RBCs do not have cell organelles including nucleus, mitochondria, ribosomes, centrioles and endoplasmic reticulum.
5. Thus almost entire cytoplasm is filled with haemoglobin.
6. In the absence of cell organelles, the consumption of oxygen is very low.
7. Anaerobic respiration occurs in RBCs.
8. Haemoglobin is a conjugated protein which is made up of a protein called globin and a non protein group heme (= haeme), hence the name haemoglobin.
9. Quantity of Haemoglobin in RBCs. 100 ml of blood of a normal man contains about 15g of haemoglobin and of normal woman an average of 13 g of haemoglobin.

LIFE SPAN -

The life of a RBC is about 120 days.

PUT NOTE -

1. Amphibian RBCs are the largest among vertebrates.
2. Salamander (Amphiuma means ) has largest RBCs about 80 mm in diameter.
3. Musk deer (Tragulus Javanicus ) has the smallest RBCs (1.5 mm)
4. The absence of nucleus in mammalian RBCs helps to accommodate maximum amount of haemoglobin.
5. Concave surface of mammalian RBCs helps in increasing the surface area.
6. RBCs of mammal lose nucleus during reticulocyte stage.
7. The adult haemoglobin molecule is made of 2 a chains with 141 amino acids each and 2 bchains with 146 amino acids each.
8. People living in hills have more RBCs.
9. Prawns, crabs and Pila contain a blue copper protein complex pigment called haemocyanin.
10. Some annelids contain green iron protein pigment called chlorocruorin.

Rouleaux -

1. In resting and slow flowing blood, the RBCs aggregate to form rouleaux.
2. Fibrinogen favours rouleaux formation.

2.      Leucocytes (White Blood Corpuscles or WBCs) -

1. Leucocytes do not have haemoglobin.
2. This varies from 5,000 to 10,000 per cubic millimetre of blood in humans.
3. Abnormal increase of WBCs is in malignancies like leukamia (blood cancer).
4. Fall in WBC count is called leukopenia.

Structure -

1. A leucocyte consists of cell membrane, nucleus and cytoplasm.
2. The cytoplasm contains mitochondria, Golgi apparatus, centrioles besides other cell organelles.

Types -

The leucocytes are of two main types- Agranulocytes and Granulocytes.

(i)      Agranulocytes -

1. The granules are not found in the cytoplasm of these cells.
2. The agranulocytes are of two types.

(a) Lymphocytes -

1. They are smaller in size containing scant cytoplasm with large rounded nucleus.
2. They are nonmotile and nonphagocytic.
3. They produce antibodies to destroy microbes and their toxins reject grafts and kill tumour cells.
4. They also help in healing of injuries.
5. Lymphocytes exist in two major groups in circulation.
6. These are B- and T-lymphocytes. (b) Monocytes -
7. They are the largest of all types of leucocytes and somewhat amoeboid in shape.
8. They have much cytoplasm. The nucleus is bean-shaped.
9. They are motile and phagocytic in nature and engulf bacteria and cellular debris.
10. Generally they change into macrophages after entering tissue spaces.

(ii)     Granulocytes -

1. They contain granules in their cytoplasm. Their nucleus is irregular or lobed or subdivided.
2.  According to their staining property, the granulocytes are divided into three types.

(a) Eosinophils -

1. The nucleus is two lobed. They have coarse granules. Their granules take acidic stains (e.g., eosin).
2. Their number increases in people with allergic conditions such as asthma or hay fever.
3. They also help in dissolving blood clot. They are nonphagocytic.
4. They seem to play a part in the immune system. They have some similarity to lysosomes.
5. Eosinophils can attach themselves to parasitic forms and cause their destruction by liberating lysosomal enzymes on their surface.

(b) Basophils -

1. The nucleus is usually three lobed. They have less number of coarse granules.
2. Their granules take basic stain (e.g., methylene blue) strongly.
3. They release heparin, histamine and serotonin. They are probably like mast cells of connective tissue.

(c) Neutrophils -

1. The nucleus is many lobed. They have fine granules. They stain weakly with both acid and basic stains.
2. Neutrophils are the most numerous of all leucocytes.
3. They eat harmful germs and are, therefore, phagocytic in nature.

Formation -

1. Formation of leucocytes is called leucocytosis or leucopoeisis.
2. The granulocytes and monocytes are formed only in bone marrow. Lymphocytes are produced mainly in lymph - nodes, spleen, thymus, tonsils, bone marrow and Peyer's patches of small intestine.

Life Span -

1. The life of the granulocytes once released from the bone marrow is normally 4 to 8 hours circulating in the blood and another 4 to 5 days in the tissues.
2. The monocytes also have a short life span of 10 to 20 hours.
3. The lymphocytes have life spans of few days or months or even years, but this depends on the body's need for these cells.

3.      Thrombocytes (= Blood platelets)

1. Platelets are colourless.
2. In mammals thrombocytes are called blood platelets.
3. They are fewer than the RBCs and more than the WBCs in number.
4. There are about 250,000 platelets in a cubic millimetre of blood.
5. Increase and decrease in the number of platelets is known as thrombocytosis and thrombocytopenia respectively.
6. Blood platelets are really cell fragments rather than true cells.
7. They are rounded or oval disc like bodies. Platelets are 2-3 micrometres in diameter.

Spindle Cells (= Thrombocytes) -

1. These are found in vertebrates other than mammals.
2. It means they are found in cyclostomes, pisces, amphibians, reptiles and birds.
3. As the name indicates, they are spindle-shaped.
4. They have well developed spherical or oval nucleus and granular cytoplasm.
5. The spindle cells help in clotting of blood like the blood platelets of mammals.