WHAT IS HAEMOPOIESIS?

 

HAEMOPOIESIS

What you need to know 

Haemopoiesis is the process through which all the blood's and plasma's cellular components are produced. It occurs inside the hematopoietic system, a collection of organs and tissues that includes the bone marrow, liver, and spleen. 

Where does it happens

     The bone marrow is the primary site of haemopoiesis in mature humans. It includes a varied population of haematopoietic stem cells, which are stimulated to differentiate into adult blood cells by a variety of biochemical signals that are released from the bone marrow. Spongy bone and compact bone are the two types of bone that exist in the human body's bone anatomy. Spongy bones contain crimson marrow, which is made up of veins that carry blood. It has a high concentration of blood stem cells, red blood cells, white blood cells, and platelets. There are just a few cells that are involved in haemopoiesis, and these include stem cells, progenitor cells, and precursor cells, among others.

    During the development of the foetus, the sites of haemopoiesis occur in the yolk sac from 0 to 2 months of age, and from 2 to 7 months of age, the sites occur in the liver and spleen until 2 weeks after delivery, respectively. However, haemopoiesis may occur in the bone marrow of the foetus when the development of the bone marrow is complete, which happens between the ages of 5 and 9 months after conception. This stage is referred to as extramedullary haemopoiesis because it is the first step of blood creation in the human body. It is the first stage of blood formation in the human body.

     Medullary haemopoiesis occurs in the bone marrow during the infants and child stage, and the majority of the red blood cells, white blood cells, and platelets are produced from stem cells in the bone marrow during this period. At this point, the majority of the bone in the newborns' skeletal system is filled with red marrow, which is characteristic of this stage.

      However, by the age of 40, the cavities in the bone marrow have been replaced by yellow bone marrow, which is primarily composed of fat, with the composition of fat and haemopoetic tissue being equal to each other. Extramedullary haemopoiesis can occur in adults if the bone marrow is no longer functional or cannot keep up with the demand for blood cells. As a consequence of this situation, the spleen and liver will grow in size. 

The Process of Haemopoiesis

     Haemopoiesis begins with pluripotential stem cells, which are also known as mother cells, since they are the cells that initiate the process of hemopoiesis in the body. This cell is immature because it has not completely developed in order to perform its functions in the body. In order for this cell to develop and function properly, it must divide into myeloid and lymphoid progenitor cells. Myeloid stem cells will differentiate into blood components such as red blood cells, white blood cells, and platelets, whereas lymphoid stem cells will differentiate into lymphocytes such as B cells, T cells, and Natural Killer cells.

ERYTHROPOIESIS

What you need to know

      The development of erythrocytes, often known as red blood cells, takes place in the bone marrow and starts with pluripotent stem cells that differentiate into progenitor colony forming cells such as BFU-E and CFU-E, which in turn differentiate into erythrocytes. The progenitor cells will undergo a series of differentiation events before becoming erythroblast precursors. It is expected that the stem cells would differentiate into myeloid progenitor cells, which will subsequently differentiate into precursor cells, which will create younger cells of the erythroblast. In the first stage, the cell will evolve into a Proerythroblast, which the division or replication occurs at this stage. This cell type is characterised by a large nucleus that occupies most of the cytoplasm, as well as a blueish colour and a larger size than the other types. Then it grows into Basophilic Normoblasts, which have a similar structure to the precursor cells but are more blue in colour than the precursor cells, and these cells produce proteins inside the bone marrow. After that, it grows into Polychromatic Normoblast, which emerges with a large nucleus that occupies most of the cytoplasm and is a little more purple than before, and it also develops into Orthochromatic Normoblast, which has a structure that is quite similar to that of Polychromatic Normoblast. Following that, it develops into a Reticulocyte, which is completely blue in colour with a nucleus that is slightly separated from the cytoplasm, and then it develops into the final stage of Haemopoiesis, which produces the perfect structure of an Erythrocyte, which is red in colour and does not contain a nucleus.

LEUKOPOIESIS

What you need to know

The formation of white blood cells or called as leukocytes that are responsible as Antibody synthesis, direct cell-mediated death of infected and tumour cells, and modulation of the immune response.

The Formation Process

       Leukopoiesis consist of 3 different types such as Granulopoiesis which is the formation of granulocytes cells such as neutrophil, eosinophil and basophils, Monopoiesis which is the formation of monocytes and Lymphopoiesis the formation of lymphocytes that are B and T cells. Initial stages of Granulopoiesis begin with the development of Myeoblast Promyelocyte cells, which differentiate into three different types of myelocytes which is Basophilic Myelocyte, which develops into Metamyelocyte and Band and eventually produces Basophils, Neutrophilic Myelocyte, which develops into Metamyelocyte and Band and eventually produces Neutrophils, and Eosinophilic Myelocyte, which develops into Metamyelocyte, Band and eventually produce Eosinophils.

     It is only the stem cells that divide into Monoblasts, which then mature into Promonocytes, and finally become Monocytes, that are involved in the Monopoiesis stage.

THROMBOPOIESIS

What you need to know

The formation of thrombocytes or can be called as platelet that function as the blood clotting factors in our body. 

The Formation Process

After the pluripotent stem cells have developed into early stage thrombocytes, which is an Early Megakaryoblast, the process progresses to the development of the Megakaryoblast. Afterwards, it progresses to the formation of Megakaryocytes, which in turn create Platelets in the peripheral circulation, and finally to the formation of Platelet aggregate.

REFERENCES

• Crumbie L. (2017, October 2). Hematopoiesis: Definition, embryology and cell lines. Kenhub. Retrieved October 27, 2021, from https://www.kenhub.com/en/library/anatomy/histology-of-hematopoiesis

• Crumbie, L. (2017, August 25). Bone marrow histology. Kenhub. Retrieved October 27, 2021, from https://www.kenhub.com/en/library/anatomy/histology-of-bone-marrow

• Pescarmona, G. (2007, October 20). Bone marrow. Biochimica Clinica. Retrieved October 28, 2021, from https://flipper.diff.org/app/items/info/550

• Villinies Z. (2012, September 27). What to know about hematopoiesis. MedicalNewsToday. Retrieved October 27, 2021, from https://www.medicalnewstoday.com/articles/319544