The blood contains three types of cellular elements namely red blood cells, white blood cells and platelets. But some of these are not typical cells because they do not possess all the characteristics of typical cells. For this reason, these cellular elements of blood are more reasonably called as blood corpuscles or the formed elements of blood.
Now we shall keep our attention about red blood cell (corpuscles) or RBC.
What is RBC?
The formed elements of blood which contain the red pigment haemoglobin for carriage of civilian are called red blood corpuscles or erythrocytes or simply the red blood cells. It was first observed in fish blood by the Dutch scientist Anton Van Leeuwenhoek in 1674 with the help of microscope devised by him.
Structure of RBC: –
The mammalian red blood cells (corpuscles) are circular, biconcave, disk-like structures. Central portions are less thick than the outside edge of the RBC and hence they appear as biconcave. The red blood cells are soft, flexible and elastic in nature, so that they can easily squeeze and pass through the fine capillaries and again acquire their original shape. The average diameter of red cells is 7.2 µm. Their outer edge and Central portions are about 2.2 µm and 1.0 µm thick respectively. The match your red cells are non-nucleated in man and other mammals and for this reason the central portion of these red blood cells exhibit a depression.
In mammalian RBC, the absence of nucleus has its great advantage. It keeps the rate cells their biconcave shape and makes room for more haemoglobin. Due to biconcave shape it allows considerable alteration of the cell volume without increasing tension of the cell membrane and it allows easy folding of the red cells when the cells passes through the fine capillaries. The biconcavity also helps to distribute the haemoglobin in a thin layer which facilitates gaseous exchange.
The red blood cells are filled with red pigment known as haemoglobin (Hb) which is an iron containing chromoprotein. It is made up of an iron prophyrin compound called heme and a protein called globin. The normal red blood cells show an incipient tendency to cling together in chains which is called rouleaux formation.
Content of RBC: –
The total count (TC) of RBC in normal adult is about 5 million per cubic millimetre in case of male and about 4.5 million per cubic millimetre in case of a female. Reduction in the number of freight cells below normal is known as anaemia and an abnormal increase in the red cell count is called polycythaemia. The aboriginal volume of a red blood cell is about 87 femtolitres (10-15 litres). The average amount of haemoglobin present in a single, normal mature red cell is about 29 pg (pg=10-6).
Origin of RBC: –
In the early foetal life, the red blood cells are formed in the liver, spleen and thymus. But later foetal life, this function is taken over by the red bone marrow which continues to act as the only site of red blood cell formation in the post-natal life. From the post natal life to before puberty all the bones contain red marrow and activity participate in red cell formation but after puberty, the marrow of long bones become in active and red cell formation is carried out by the applied bones only because they contain the red marrow.
A large stem cell called hemocytoblast, from which a red cell originates and the process of formation of the cell is called
Formation of RBC in the bone marrow is controlled by a glycoprotein named erythrocyte stimulating factor or ESF or erythropoietin. If there is a lack of oxygen supply in the body, the kidney secretes an enzyme erythrogenin, in plasma which produces erythropoietin from a plasma protein fraction. The erythropoietin intern stimulates the red bone marrow to produce RBC. In this process the production of red blood cells is nicely adjusted according to the need of oxygen supply in the body.
Lifespan of red blood cells: –
The average lifespan of red blood cell is 120 days, after which the circulating senile rate cells become breakable and are phagocytosed by the macrophages or reticulo-endothelial cells or RE cells of liver, spleen and bone marrow. The heme which is the part of haemoglobin released from the broken red cells is catabolised form bilirubin and biliverdin that are excreted in the bile as the bile pigments. On the other hand the iron and the globin of haemoglobin are reused for red blood formation.
Functions of RBC: -
The basic three functions of RBC are as follow:
i) Gas transportation – the red blood cells has very important role in transportation of the respiratory gases that is oxygen and carbon dioxide. The haemoglobin carries oxygen and carbon dioxide by performing the compounds Oxy haemoglobin and carbaminohaemoglobin respectively.
ii) Acid-base balance – the haemoglobin of red blood cells forms a buffer system and helps to maintain acid-base balance or pH balance of the body.
iii) Maintain viscosity and specific gravity – the red blood cells determined a viscosity and specific gravity of blood which is directly proportional to the number of red blood cells.