Hematopoiesis

00:00 Let us now look at some of the details of hematopoiesis. Firstly, it is important to know that all the blood cells that circulate in the blood have a very limited lifespan.

00:15 Red blood cells only have a life span of 120 days, neutrophils even less. So it is important that we have a tissue that continually renews all these blood cells and that is the process of hematopoiesis and it occurs in the bone marrow. The original stem cell that gives rise to all the lineages is called the hematopoeitic stem cell. It is a pluripotent stem cell. It is obviously a very important cell. It sits in the bone marrow.

00:54 It divides over and over again and it gives rise to the progenitor cells, which in turn go through all the process of providing lineages leading to the production of all the different blood cell types. So it is important that this hematopoietic stem cell divides continually to provide these progenitor stem cells as well because they are lost during the process of their differentiation into the final blood cell types. There are a number of different colonies that arise from these hematopoietic stem cells. One is the common lymphoid progenitor cell types that give rise to the lymphocytes and I am not going to talk about in this lecture.

01:48 Then there are the rather common myeloid progenitor cells of which have different progenitor cell populations that are then influenced by a number of factors that is not the scope of this lecture. A number of factors then stimulate these lineages to go through various processes of developing into the various cell types, erythrocytes, the white blood cells, megakaryocytes and the platelets. So in this lecture, I am going to concentrate on the lineage that is derived from the megakaryocytes, erythrocytes, progenitor cell. And then I am going to talk about the lineage that gives rise to the neutrophil, the lineage that is derived from a granulocyte, monocyte progenitor cell. But appreciate there are different colonies of these progenitor cells and as I've said they are influenced by a number of factors some of which are listed on this slide.