Red blood cells Structure | Their Source and Functions
Red blood cells are one of the type of blood cells.
They are the widely distributed cells in the blood.
They are named as red cells as they are red in color.
They impart red color to the whole blood due to which our blood is red.
These are also called as blood corpuscles because they are like coins and corpuscle in shape.
Further they float freely in the blood due to their shape and low weight.
They are also termed as erythrocytes and are abbreviated as RBC’s.
They are formed in the red bone marrow of long bones by the process known as erythropoesis.
Red blood cells have a life span of 120 days. During their continuous flow inside the blood vessels, they get worn out.
Their membranes become fragile and break down in the endothelial reticulum of spleen.
Then they are removed from the blood completely by liver.
Liver metabolizes their breakdown products into bile pigments viz. bile-rubin and bili-verdin and the iron (heme) liberated is reused.
Red blood cells Structure
The blood corpuscles as shown in pic are biconcave shaped discs. They have a mean diameter of 7.8 micrometers.
And by thickness, they have a width of 2.5 micrometers at the thickest point and 1 micrometer or less in the center.
Their volume is 90 to 95 cubic micrometers.
Red blood cell count:
The concentration of red blood cells per cubic millimeter is 5,200,000 in men and is 4,700,000 in women.
Their decline is seen during pregnancy, severe menstruation disorders in women and in all due severe disease conditions. Decrease in red cell count or abnormality in their shape results in anemia.
Source of red blood cells:
They are formed in the red bone marrow of long bones.They internally have a pigment called hemoglobin. This hemoglobin is made of heme (iron) and protein globulin part.They combine to form a protenacious substance in complex with iron molecules. This pigment helps to carry oxygen by these cells.
Their main function is to transport of gases like oxygen and carbon-dioxide.
1. Transport of oxygen: They transport oxygen from the lungs of respiratory system to all the tissues and cells in the body. They do it by reversible combination of oxygen with hemoglobin within them. When the RBC’s flow through the alveoli of lungs, the oxygen exchanges between alveolar tissue and hemoglobin until hemoglobin gets saturated. At the point of saturation, in a healthy individual, 1 gram of hemoglobin holds 1.39ml of oxygen.
For determining the oxygen level in blood see to this page describing amount of oxygen in blood.
Oxygen is present in dissolved form and also in bound form to hemoglobin.
2. Transport of carbondioxide: They help in transport of carbon dioxide from tissues to lungs. They contain carbonic anhydrase enzyme that catalyzes the reversible reaction between carbon dioxide (CO2) and water to form carbonic acid (H2CO3), thereby increases the rate of the reaction. Thus formed carbonic acid is transported by water in the blood.
Also some amount of carbon dioxide can bind to hemoglobin directly.
3. pH Maintenance: The pH of blood is 7.3 and it is always kept constant by homeostasis. The presence of hemoglobin act as acid-base buffer, thus the red blood cells beside other factors are responsible for the acid-base buffering power of whole blood.