WHAT IS HAEMOPOIESIS ???

"A journey of a thousand miles begin with a single step. And for blood, haemopoiesis is the start of it all. If you doesn’t know what is it, don’t worry, you are not stupid. Just a bit ignorant, I guess. Well, that is why in this week entry, we are going to tell you the ins and outs of haemopoiesis."

HAEMOPOIESIS

Haemopoiesis is the production of all of the cellular components of blood and blood plasma, including our loyal subordinates, leukocytes or commonly known as white blood cells, red blood cells or erythrocytes and platelets or also known as thrombocytes. In a simple word, haemopoiesis is all about how our blood is created to serve the human being.

Haemopoiesis basically takes place within the haemopoietic system which including organs and tissues such as bone marrow, spleen and liver. It occurs in many places depending on the age of the individual. Table below shows the specific sites of the haemopoiesis based on our age:

Age	Site of hematopoiesis
Embryo	yolk sac then liver
3rd to 7th month	spleen
4th and 5th months	marrow cavity - esp. granulocytes and platelets
7th month	marrow cavity - erythrocytes
Birth	mostly bone marrow; spleen and liver when needed
Birth to maturity	number of active sites in bone marrow decreases but retain ability for hematopoiesis
Adult	bone marrow of skull, ribs, sternum, vertebral column, pelvis, proximal ends of femurs

Haemopoiesis might seem complicated but this process is the most important part of the journey. This long and strenuous process occurs during embryonic and throughout the adulthood is to produce and replenish the blood in our body system. During embryonic phase, the primitive haemopoiesis is significant to ensure the tissue oxygenation is in a good condition as the embryo undergoes the rapid growth and development.

To provide a complete and thorough information, as well as to make sure our faithful readers are able to comprehend this process, let us tell you this process step by step.

THE PROCESS OF HAEMOPOIESIS

Ø At the embryonic phase, haemopoiesis first occurs in the yolk sac of an embryo and later move to the liver, spleen, thymus as well as the lymph nodes of the fetus. Red bone marrow becomes the primary site of haemopoiesis in the last 3 months before birth, it will then continue as the source of blood cells right after birth and also throughout life.

Ø About 0.05 to 0.1 % of red bone marrow are called PLURIPOTENTIAL STEM CELLS which derived from the mesenchyme. These cells are known as pluripotential as it has ability to develop and differentiate into various type of cells. These stem cells are able to reproduce themselves, proliferate and differentiate into cells that give rise to erythrocyte (red blood cells), leukocyte (white blood cells) which further divided into five different cells, as well as thrombocyte (platelete).

Ø To produce blood cells, pluripotential stem cells will synthesis two further types of stem cells, which then will give rise to several types of cells by differentiation process. These stem cells are called myeloid stem cells and lymphoid stem cells.

Ø Myeloid stem will then develop into red blood cells (erythrocyte), platelets (thrombocyte), monocytes, neutrophils, eosinophil, and basophils. On the other hand, lymphoid stem cells will develop to become lymphocytes.

Ø During haemopoiesis, some of the myeloid stem cells will develop into progenitor cells at the first point, meanwhile other myeloid stem cells and lymphoid stem cells will directly develop into precursor cells.

Ø In fact, progenitor cells is actually unable to differentiate to reproduce themselves, however they are committed to give rise into specific elements to aid the formation of blood cells. Some of the progenitor cells are known as colony-forming units (CFUs). Generally, CFU production was designed to indicate the mature cells that they will form later. For instance, CFU-E ultimately produce erythrocytes, CFU-Meg indicate the megakaryocytes (the source of platelets), and CFU-GM will indicate to things, G is for granulocyte cells while M is for monocyte.

Ø In another instance, precursor cells are known as blasts. After several cell divisions undergo by the stem cells, it develop into the actual form of the blood cells. For example, monoblasts will develop into monocyte, eosinophilic myeloblasts will develop into eosinophils and so on.

Ø Haemopoiesis process was also influenced by the haemopoietic growth factors in order to regulate the differentiation and proliferation of particular cells. One of it is erythropoietin, which mainly produce by the tubular cells of kidney to increase the number of red blood cells precursor. Next is thrombopoietin, which is a hormone produce mainly in liver helps to stimulate the production of platelets from megakaryocytes. Lastly is cytokines, which is the small glycoprotein that produce by the cells of red bone marrow in order to stimulate the proliferation of the progenitor cells within the red bone marrow. In fact, cytokines such as colony-stimulating factor and interleukins are vital in the stimulation of white blood cell formation.

Ø By referring to the flowchart above, we can clearly comprehend how is basically the blood cells is form from its stem cells, progenitor cells as well as the precursor cells.

"Complicated? Well, this is the simplest explanation for this process, okay. A good process produces a good result. Although, I’m sure most of you are not pleased to read this lengthy information, you still need to comprehend this process in order to know the correct way to maintain your health. Slow down, calm down, don’t worry and don’t hurry. You have an entire lifetime to digest all of this information. If by chance, you still have problem to understand this process, feel free to leave comment on this blog. We will do our best to satisfy your curiousity!"