Bone Marrow and Hematopoiesis

00:01 In this lecture, you are going to learn about the histological structure of bone marrow and the process of hematopoiesis. Sometimes the word hematopoiesis is also written and pronounced hemopoiesis. So I might use both terms intermittently throughout these lecture, but understand that hematopoiesis and hemopoiesis are the same process.

00:29 Well, in this lecture, I am just going to briefly cover some of the major lineages or major processes whereby stem cells can give rise to progenitor cells and each of those populations of progenitor cells can then give rise to the blood cells. And in this lecture, I am only going to cover the lineage that gives rise to the erythrocytes, red blood cells and as an example of the granulocytes I am going to look at the lineage that gives rise to the neutrophil. So in other words, I am going to describe the events called erythropoiesis, manufacturing or giving rise to red blood cells and granulopoiesis giving rise to the granulocytes of which only the neutrophil is going to be the example I am going to use.

01:34 Now bone marrow has a number of functions. It is an enormous tissue. It is important to give rise to all the blood cells. It produces all the blood cells and then releases those blood cells into the blood once they are in the mature functional form. Blood sinusoids or blood capillaries, special vessels in the bone marrow are very important to maintain a barrier between the circulation containing normal blood cells and all the cells that are undergoing all their training and development. I am not going to talk about the blood sinusoids in this lecture, but I just want to stress that they do form a very important barrier so that external factors do not interfere with the process of hematopoiesis and the training of all these different blood cells to be able to do their job once they are released into the circulation. I will talk about blood sinusoids in more detail when we look at the cardiovascular system and other systems. Hematopoiesis includes formation of the red blood cells, the white blood cells and also the thrombocytes or platelets.