Red Blood Cell - Structure And Function

Blood is composed of 2 major components; blood cells, and plasma. Plasma occupies approximately 55% of the total blood volume, and the remainder is occupied by white blood cells, platelets, and red blood cells. Red blood cell is the most abundant type of cells in blood. Normal red blood cells are biconcave discs, having a mean diameter of 7.8 micrometers, and a thickness of around 2.5 micrometers. The average volume of a single red blood cell is about 90 to 95 cubic micrometers. The average count of red cells in a healthy male is about 5.2 million cells per cubic milliliter, and in women, it’s around 4.7 million cells per cubic milliliter. Red cells can change their shape remarkably as they squeeze through capillaries. In fact, they can get deformed into almost any type.
During the early weeks of embryonic life, primitive, nucleated red cells are produced in the yolk sac. In the second trimester, liver is the main organ to produce red cells, although spleen and lymph nodes also produce small amounts. During the last month or so of gestation, and after birth, red cells are produced exclusively by the bone marrow.
This graph shows the relative rates red blood cell production by different types of bones after birth. Red cell production is stimulated by erythropoietin hormone. And vitamin B12 and folate are essentially required for the synthesis of red cells. For a more comprehensive lecture on red cell production, you can watch my erythropoiesis video, the link is in the description below. The average lifespan of a red cell in a healthy individual is around 120 days. Older red cells are destructed mainly by the spleen.
Mature red cells do not contain nuclei, mitochondria, or an endoplasmic reticulum. However, they contain cytoplasmic enzymes that are capable of synthesizing ATPee. In addition to that, these enzymes maintain the membrane flexibility of red cells. Maintain transport of ions through the red cell membrane. Keep the iron in hemoglobin in the ferrous form. And prevent oxidation of red cell proteins.
The main function of red cell is to transport hemoglobin, which in turn, carries oxygen from the lungs to the tissues as oxy hemoglobin. The average hemoglobin concentration in red cells is 34 g per 100 ml of cells. They also transport carbon dioxide from the tissues to the lungs as carb amino hemoglobin to excrete carbon dioxide from the body in exhaled air.
Red cells have other functions besides transporting oxygen and carbon dioxide. For instance, they contain a large quantity of carbonic anhydrase enzyme, which catalyzes the reversible reaction between carbon dioxide and water to form carbonic acid, increasing the rate of this reaction. The rapidity of this reaction increases the ability of blood to transport enormous amounts of carbon dioxide in the form of bicarbonate. In addition, hemoglobin is an excellent acid base buffer. Therefore, red cells are responsible for most of the acid base buffering power of whole blood.

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