Hematopoiesis

• Hematopoiesis, also known as Hemopoiesis, is the formation of RBCs, WBCs and platelets.
• Prenatal Hematopoiesis begins in the mesoderm of the yolk sac where mesenchymal cells aggregate into clusters, blood islands, and primitive nucleated erythrocytes are formed.
• The Mesoblastic Phase of Prenatal Hematopoiesis is in the mesoderm of the yolk sac where mesenchymal cells aggregate into clusters, blood islands, and primitive nucleated erythrocytes are formed.
• The Hepatic Phase of Prenatal Hematopoiesis is in the liver, where definitive enucleated erythrocytes and some leukocytes appear.
• The Splenic Phase of Prenatal Hematopoiesis is in the spleen.
• The Myeloid Phase of Prenatal Hematopoiesis is in the bone marrow.
• Postnatal Hematopoiesis occurs almost only in the bone marrow, lymphatic organs, and spleen, and if necessary, extramedullary hematopoiesis resumes function.
• More than 10^11 blood cells are produced daily in the bone marrow.
• Multipotent partially differentiated cell lineage pluripotent HSCs.
• Postnatal Hematopoiesis is a continuous process that maintains a constant level of different cell types in the body.
• Bone marrow is a soft, gelatinous, highly vascular and cellular tissue that constitutes almost 5% of the total body weight.
• Stromal cells are supporting cells in bone marrow, including endothelial, adipocytes, and fibroblasts.
• Numerous cytokines and growth factors act on specific stem cells, progenitor cells, and precursor cells by inducing mitosis and/or differentiation.
• Hematopoietic stem cells (HSCs) are pluripotent and can self-renew and differentiate by various growth factors and cytokines, giving rise to all blood cell types.
• Red bone marrow, also known as medulla ossium rubra, consists mainly of hematopoietic tissue including red blood cells, platelets and most white blood cells.
• Hematopoiesis occurs in the bone marrow, specifically in the medulla ossium, which is located in the medullary cavity of long bones and the spaces between trabeculae of spongy bones.
• Common myeloid progenitors and common lymphoid progenitors have the capability of self-renewal and committed differentiation.
• Yellow marrow, also known as medulla ossium flava, is mainly made up of fat cells and does not support hematopoiesis.
• Monocytes mature into azurophilic granules and lysosomes.
• Thrombopoietin increases polyploidy as much as 64 times before chromosomal replication ceases.
• In mammals, B cells are originate d in several sites including the marrow, the gut-associated lymphatic tissue, and the spleen.
• Precursor T cells leave the bone marrow, proliferate and mature in the Thymus into T cells.
• Monocytes in circulation last for 1-2 days before differentiating into macrophages.
• Lymphatic organs such as lymph nodes and spleen are sites of proliferation of lymphocytes.
• Platelets mature into megakaryocytes, which endomitosis and produce platelet-producing megakaryocytes with scattered azurophilic granules.
• Monocytes are produced at a rate of 10^10 cells per day.
• Monocytic maturation takes 55 hours.
• Trombocytopoiesis, also known as thrombocytopoiesis or thrombopoiesis, is the production of platelets, also known as thrombocytes.
• Granulocytic maturation, also known as granulocytic opoiesis, is the production of neutrophils, eosinophils, and basophils.
• Cells in thrombopoiesis do not divide, become larger, and the cytoplasmic and nuclear degenerate and are phagocytosed by macrophages.
• Neutrophils, eosinophils, and basophils are produced in hematopoiesis.
• Platelets are produced at a rate of 10^6 cells per day.
• Neutrophils leave the hemopoietic cords by piercing the endothelial cells lining the sinusoids and in the circulatory system they marginate, adhering to the endothelial cells of blood vessels and remaining there until needed.
• Growth factors are delivered to the body through the bloodstream, endocrine hormones, secretion by stromal cells of bone marrow, paracrine hormones, direct cell-to-cell contact, and surface signaling molecules.
• Neutrophils, eosinophils, and basophils are produced in granulopoiesis, which takes approximately two weeks in the bone marrow.
• Granulocytopenia, or a decrease in granulocytes, can lead to tissue hypoxia and infections.
• Granulocyte-CSF, Monocyte-CSF, IL2, IL5, IL6, IL11, and IL12 are examples of cytokines.
• Granulocytopenia can be caused by a decrease in the production of granulocytes, an increase in the destruction of granulocytes, or a combination of both.
• Steel factor and stem cell factor are examples of growth factors.
• Macrophage inhibitory protein-α (MIP-α) is an example of a cytokine.