Erythrocytes

Erythrocyte which is commonly called as red blood cells (RBC) is a component of blood. A single blood drop contains around millions of erythrocytes and many thousands of leukocytes. Erythrocyte is made in the bone marrow and contains protein which is called as hemoglobin. There is a difference of amount of erythrocyte in the blood cell; the males have around 5.44 million of erythrocyte per microliter of blood and females have around appropriately 4.8 million per microliter. It is estimated that the erythrocyte makes up about 25 percent of the total cells in the body. The predominant function of the erythrocyte is to carry the inhaled oxygen from the lungs and to transport it to the tissue of body. Erythrocyte carries about 24 percent of carbon dioxide waste from the tissue and transports it to lungs for the process of exhalation.

Anatomy of Erythrocytes

Shape and Structure of Erythrocytes

The mature stage of erythrocytes is in red bone marrow of the body. The erythrocytes are structured like biconcave disc: that is they are plump at their periphery and very thin at the center. The erythrocytes lack most organelles and thus having more interior space therefore the hemoglobin molecules are occupied in order to transport gases to the lungs. The biconcave shape of the erythrocytes provide greater surface area in which the exchange of gases occurs, relative to its volume. The shape of the erythrocytes optimizes the ratio of surface area to volume this also enables them to fold as they move through the narrow blood vessels. In the capillaries, the gas that is oxygen which is carried by the erythrocytes can diffuse into plasma and then through the capillary walls to reach the cells, whereas some percent of carbon dioxide which is produced by the cells as a waste product diffuses into the capillaries in order too picked up by the erythrocytes. The capillary beds are very narrow which slows the passage of the erythrocytes which provides an extended opportunity for exchange of gases. It is marked that the space within the capillaries can be so minute and thin that even with their small size; erythrocyte can fold and make their way through the vessels. The erythrocytes, possess structural protein like spectrin, which are flexible in nature which allows them to bend over to a certain degree and make them spring back when they enter to a wider space.

Lifecycle of erythrocytes

The production of new erythrocytes is carried out through a process called as erythropoiesis. The whole process takes around seven days developed from committed stem cells. When they get matured these cells circulates in the blood stream for around 100 to 120 days performing their overall function in the body that is transportation of gases. Later they get degraded and are removed from circulation at the end of their life span. Erythrocytes are constantly produced in the red bone marrow of large bones producing 2 million cells per second in a healthy human body.

The erythrocyte differentiates from erythrotropietic bone marrow cells, a type hemopoietic stem cell found in bone marrow. The bone marrow cells contains nucleus unlike erythrocyte. The liver is the main site of the red blood cells production in the embryo and nears similar types of steam cells at this stage of development. The stem cells are converted into erythroblast and then reticulocyte. The reticulocytes are released into the bloodstream where they mature into erythrocytes. The old and damaged erythrocytes are phagocytized by macrophages in the bone marrow, liver and spleen. The globin protein which is broken down into amino acids, are refused for protein synthesis. The cell components like organelles, membrane, and structure are also recycled. The hemoglobin that is not phagocytized is broken down in the circulation releasing alpha and beta chains that are removed from the circulation by the kidney. The iron contained in the heme portion is stored in the liver or may be spleen in the form of ferritin o hemosiderin or carried through the blood stream by transferrin to red bone marrow for further recycling of erythrocytes. The heme portion is broken down into biliverdin for transportation in the blood which is a waste product; bilirubin is another waste product a yellow pigment. The unused heme group can be recycled and used in erythropoiesis.

Haemoglobin

The haemoglobin molecule is composed of four heme groups which is surrounded by a globin group, forming a tetrahedral structure. Heme, which holds only 4 percent of the weight of the molecule, is comprised of an ring-like organic compound which is referred as porphyrin to which an iron atom is attached. Haemoglobin carries oxygen from the lungs to the tissue and also helps in transportation of hydrogen and carbon dioxide ions back to the lungs.