Our hematopoietic system has too many secrets that are not known to us. They are hard-working and dedicated to us, and we should know them, love them, and make them work better for us. Our hematopoietic system is one of the most proliferating and renewing organs in our body. The blood that flows in our blood vessels is made up of blood cells and plasma. Blood cells, also known as “hemocytes”, are cells that are present in the blood and can travel throughout the body with the flow of blood. The red color of our blood is due to the red color of red blood cells, which make up about half of the blood. In addition to red blood cells, there are also white blood cells and platelets, but they occupy a smaller share, but their function is very important. During the life of the organism, blood cells are constantly metabolized. Every day, some of the senescent blood cells are destroyed, while some new blood cells enter the circulation. The average life span of red blood cells is about 120 days, that of white blood cells is in hours, and that of platelets is a few days, as measured by isotope labeling. Therefore, in clinical practice, after transfusion of blood (mainly concentrated red blood cells) in some patients, if the disease itself does not improve, soon, the red blood cell count will drop again. The same holds true for platelet transfusions. White blood cells are rarely transfused clinically because of their short life span in the body and the greater risk of transfusion (possible rejection). The two processes, production and destruction of blood cells, maintain a dynamic balance. Therefore, the number of blood cells in the blood of a normal person remains relatively stable. What does such a rapid renewal rate rely on, while maintaining normal function? Blood cells are derived from hematopoietic pluripotent stem cells in the bone marrow. They are a very small group of cells that are the “grandparents” of our blood cells that can be renewed at any time. They have two main characteristics: they can differentiate into the next lineage of blood cells, and they can replicate themselves to maintain their stability. However, in general, they are not in a proliferative state, but in the resting G0 phase. In mammals, blood cells contain the following three main components: Erythrocytes: The main function is to transport oxygen and maintain the oxygen needs of each organ to maintain its normal function. Leukocytes: mainly play the role of immunity. When pathogenic bacteria or foreign bodies invade the body, or when there are senescent or dead cells or malignant cells of their own, leukocytes can cross the capillary walls and concentrate on the site of the lesion and engulf it. Platelets: play an important role in the process of hemostasis. Among blood cells, only white blood cells have nuclei, while mature red blood cells and platelets are non-nucleated. The human hematopoietic system begins to develop during fetal life, and after birth, hematopoietic tissues are mainly concentrated in the bones of the whole body. In adulthood, hematopoietic cells mainly originate from the bone marrow in the human skull, ribs, sternum, spine, and pelvis, which is why iliac bone marrow aspiration is often performed when hematologic disorders are suspected. The sternum, too, is a commonly used site for bone marrow aspiration, while other bones such as ribs, skull, and vertebrae are generally used sparingly in clinical practice due to the difficulty and high risk of puncture. The blood flowing in the blood vessels is called peripheral blood, while the blood in the bone marrow is called bone marrow blood, referred to as “bone marrow”, and most diseases of the blood system require bone marrow collection to assist in diagnosis. Under normal circumstances, peripheral blood cells include red blood cells, white blood cells and platelets, and white blood cells include neutrophils, lymphocytes, monocytes, eosinophils, basophils and plasma cells, which are also called mature blood cells. In bone marrow blood, in addition to these mature blood cell components, there are some naive cells (progenitors of these mature cells at all levels), such as primitive and naive granulocytes, primitive and naive erythrocytes, megakaryocytes (progenitors of platelets), etc., which are called hematopoietic cells; there are also some non-hematopoietic cells in bone marrow, which are stromal cells that support hematopoietic cells, like the soil in which blood cells grow and develop, including adult Fibroblasts, histiocytes, adipocytes, etc. With the development of medicine, some blood cells (derived from the lymphatic system) in very small numbers, such as NK cells, dendritic cells, and Langerhans cells, have also been gradually recognized. In conclusion, blood cells originate from hematopoietic pluripotent stem cells in bone marrow, which first differentiate into colony-forming unit cells (bone marrow stem cells) and lymph-like stem cells, and then differentiate into directed stem cells of various lineages from bone marrow stem cells, which develop and proliferate through primitive and naive stages and finally mature into erythrocytes, granulocytes and monocytes and platelets. Lymphocytes develop and proliferate through primitive and naive stages and mature; under the stimulation of antigen, they are transformed into prolamellar cells and proplasma cells respectively, and proliferate and mature into immunologically active lymphocytes and plasma cells. The proliferation of blood cells is carried out by division, but only naive cells have the ability to divide, and once they reach a certain stage of development and maturity. The proliferation stops.