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The Red Cells - their function, haemopoiesis and haemolysis
Being the most abundant form of cells in the human body (25 trillion in an average human being), the red cells also known as the erythrocytes function mainly as transporters of oxygen in the blood. This function is achieved mainly by the presence of a protein known as haemoglobin within the red blood cells. This protein has its unique ability to incorporate oxygen into its structure in the abundance of oxygen and to release oxygen when the surrounding lacks oxygen. Apart from this, haemoglobin also acts as an excellent buffer, helping to maintain the pH of the blood at a constant range. In addition to the transportation of oxygen, the red cells also contribute to transport carbon dioxide dissolved in plasma, by promoting its dissolution. This is by an enzyme known as carbonic anhydrase, which is also abundant in the cytoplasm of the red cells.
The Structure of a Red Cell
A red blood cell has a shape of a biconcave lens, measuring approximately 7.8 micrometers in diameter, 2.5 micrometers in thickness in the periphery and 1 micrometer in thickness at the center. It has a volume of around 95 cubic micrometers. The cell has a unique ability to change its shape and size with the assistance of the cytoskeleton made up of tubulin, ankyrin and spectrin molecules. The number of red cells in an averagely built man is 5.2 million per milliliter of blood with each 100 ml containing approximately 15 grams of haemoglobin. One gram of haemoglobin is known to transport 1.34 ml of oxygen. Therefore, the blood of an adult male carries 20 ml of oxygen dissolved in each 100 ml of blood.
Production of Red Cells - Erythropoiesis
Production of red blood cells, also known as erythropoiesis, occurs in various sites depending on the stage of the human life. In the embryo, the red cells are formed in the yolk sac and in the foetus it is seen to occur predominantly in the liver. In a child who is less than 2 years of age, haemopoiesis occurs in the shafts of the long bones, though it becomes limited to the flat bones such as the vertebrae, sternum and the iliac crest in adults. The cells are formed by the division of pluripotent stem cells which have the capacity to give rise to any form of a blood cell. The type of cells committed to form the red cells is known as a colony forming unit erythrocyte. These undergo a number of divisions and a process of maturation to form the circulating erythrocytes. The division of pluripotent stem cells to form the CFU-E is promoted by the erythropoietin, a hormone produced in the kidneys in response to hypoxia (low concentrations of oxygen in blood). In addition to erythropoietin, the red cell production is governed by a number of chemical modulators acting at the tissue level such as interleukin 3.
Destruction of Red Cells - Haemolysis
An average red cell usually has a life span of 120 days. Since the cell is deficient of a nucleus, the cell fails to regenerate the proteins that are necessary to replace and repair insults the cell faces during the circulation. As a result the cells tend to loose its ability to withstand the shearing forces. The spleen and the liver has an architecture designed to recognize these types of cells, which undergo destruction – known as haemolysis – within these organs.
An approach to anaemia......
The body should have an abundant supply of the nutrients necessary to produce red cells. These include iron – which is an essential component of the haemoglobin, vitamin B12, folic acid and proteins. Therefore, the deficiencies of these factors give rise to different types of deficiencies of haemoglobin and red blood cells – known as anaemias. Inability of the body to form and maintain the red cells structure and function also gives rise to premature destruction of red cells causing anaemias. The anaemias is a broad category of diseases and will be discussed in detail in the articles to come.