Blood forms 7% of a person's body weight and its volume may vary from one individual to another depending on the size. It is the life-maintaining fluid that circulates through the entire body, via blood vessels called arteries and veins. Blood plays a vital role in our existence as it carries oxygen, nourishment, vitamins, hormones, antibodies, heat and electrolytes to different parts of the body, which are essential for the body's proper functioning. They also carry and get rid of carbon dioxide and waste matter from the blood. The human blood is made up of 78% water and 22% solids. Blood contains plasma in which blood cells such as red blood cells (RBC), white blood cells (WBC) and blood platelets are suspended. All these components play very important roles in the body, however, in this article we will only focus on the function of red blood cells.
What are the Functions of Red Blood Cells
Red blood cells or RBCs are also referred to as erythrocytes and are the most abundantly found blood cells as compared to WBCs and platelets, accounting for about 45% of total blood volume. They are around 6 - 8 micrometers in size and the human body contains about 4 - 6 millions/mm3 of them. RBCs are biconcave lens-like cells that lack a cell nucleus and are made up of a protein called hemoglobin. In fact, 33% of RBC is nothing but hemoglobin. Embedded within this hemoglobin molecule is iron, whose function is to transport oxygen and carbon dioxide in the blood. This hemoglobin is also responsible for the biconcave shape and red color of the RBCs.
RBCs are formed in the bone marrow, under the influence of hormone erythropoietin (formed in the kidneys), by a process called erythropoiesis, in just 7 days. On maturing in the bone marrow, these cells are circulated in the body for almost 3 months before they are destroyed in the spleen, or recycled by the macrophages in the body. So the general lifespan of a red blood cell is only 3 months. Well, so what does the red blood cell do in its short lifespan and why is it so important for our existence? To understand this, we will have to look at some red blood cell functions.
The main function of the red blood cell is to transport oxygen from the lungs, to the other tissues and cells of the body. And how does the RBC manage to do this? Well, the hemoglobin present in the RBC is a protein, which binds itself to the oxygen molecules inhaled. When a person inhales, oxygen from the atmosphere enters the body through the nostril and reaches the lungs. At the lungs, hemoglobin molecules bind themselves to the oxygen molecules and move to the heart. From the heart, the same oxygen-containing blood is pumped to the rest of the body parts (muscles, tissues and other organs). The hemoglobin molecules then release the oxygen molecules to the cells of the body. Basically, hemoglobin takes oxygen from high oxygen level areas and releases them in low oxygen level areas of the body. Thus, RBCs actually perform the function of transporting life-sustaining oxygen to the different parts of the body.
Carries Carbon Dioxide
The other function of the red blood cell is to partly carry carbon dioxide, which is a waste product of metabolic activities in the body. Carbon dioxide is actually formed in the cells as a result of the chemical reactions taking place. This waste product is then excreted through the blood plasma and RBCs. While the RBCs play a major role in eliminating carbon dioxide from the cells, blood plasma also accounts for a small amount of carbon dioxide removal. The hemoglobin in the RBCs bind the carbon dioxide molecules to form carbaminohaemoglobin. However, unlike oxygen molecules, carbon dioxide molecules do not bind to the iron part of hemoglobin. Instead, they combine with the amino acid groups on the hemoglobin polypeptide chains. Thus, RBCs transport carbon dioxide from the various cells of the body and take them to the lungs, from where it is discarded by exhalation.
This round trip of transporting oxygen to the tissues and then bringing waste materials to the lungs for elimination, takes the RBCs only 30 to 45 seconds. The ability of the RBC to transport oxygen depends on several factors like pH of the blood, temperature, etc. Moreover, the presence of carbon monoxide, hydrogen sulfide, etc. in the blood also affects hemoglobin's oxygen carrying capacity.
The exact process of oxygen transfer from the hemoglobin to the tissues of the body is a complex one. However, this was a simple way of explaining the function of red blood cells. Don't be fooled by the easy explanation and think that the RBC does nothing of great significance. If at all these RBCs stop functioning, then the body will surely have life-threatening issues. Blood disorders like sickle-cell anemia, hemolytic anemia, hemochromatosis, hereditary spherocytosis and various other red cell enzyme deficiencies can occur and pose a threat to one's life.