The blood in the human body travels through vessels which are not leaky. This is an example of closed vascular circulation. Blood comprises of plasma (55%) and cellular components (45%).
Hematopoiesis
Hematopoiesis is defined as the process of forming these components. In the embryonic phase, the yolk sac does the work of hematopoiesis. In a developing fetus till the 3rd month after birth, the liver and spleen do the process and after that, the process takes place in the bone marrow.
The bone marrow in a neonate is present in all the long bones of the body, which is located in the central region of the bone. As aging occurs, this region gets substituted with fat. But there are certain bones that still contain bone marrow irrespective of age. The vertebral column, ribs, sternum, skull, sacrum, and pelvis are some of them. They are also present in the proximal ends of bones of the lower body.
There are also some conditions where the non-hematopoietic marrow can get activated. However, this is autonomous. This condition is also observed in the liver and spleen in some adults. The two main phases in hematopoiesis are proliferation (mitotic division) and differentiation (maturation).
Hematopoietic stem cells (HSC)
The hematopoietic stem cells (HSC) are identified in bone marrow by surface protein CD34. When HSCs are introduced into the blood, this surface protein is responsible for directing them into the bone marrow. These cells self-replicate and then differentiate into lymphoid stem cells and myeloid stem cells, which further differentiate into specific stem cells as displayed by the flowchart below.
Processes involved in production of blood components
Erythropoiesis- formation of RBC
Thrombopoiesis- formation of platelet and occurs by thrombopoietin
Granulopoiesis- formation of granulocyte Lymphopoiesis- formation of B and T lymphocytes
Erythropoiesis
Erythropoiesis is the conversion of HSC to RBC. This occurs in the presence of certain growth factors and hormones. The main one is erythropoietin. The flowchart below represents the process in detail. One of the characteristic features of the RBC is that they are devoid of nucleoli. At this stage the transcription ceases. Gradual necrosis of the nucleoli leads to pyknotic nuclei, where the chromatin cannot undergo condensation. Thus the cell division fails. This is observed in the orthochromatic stage. The nucleus is completely destroyed in the reticulocyte stage.
The RBC, also known as erythrocytes, consists of a lipid bilayer along with a protein bilayer. The skeleton is framed by carbohydrates, attached to the inner membrane, and is responsible for maintaining the shape of the cell. The proteins present in RBC are spectrin, glycophorin, and band proteins. The following are the nutritional requirements for erythropoiesis. Minerals- cobalt, manganese, iron Vitamin- B12, folate, B6, C, E, and riboflavin There are some cases or situations that can affect the process of erythropoiesis. These can simply be put together as the diseases affecting erythropoiesis. The most prominent disease is anemia.
Anemia
Anemia in general is known as an iron deficiency disease, but there is a lot more beyond that. Anemia is a medical condition that arises due to the reduction in the blood supply to the target site. This can be easily deciphered from the name. An- none emia- blood. There are a lot of factors that can cause this disease, but all of them can be categorized into two- decreased production of RBC and increased destruction of RBC. The next blog covers anemia in more detail.
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