Hematopoiesis

Hematopoiesis Overview

• Hematopoiesis is the process of blood cell formation
• Prof. Dr. Siti Balkis Budin lectured on this topic
• Blast cells and mature cells have differences
• Erythropoiesis and leukopoiesis are different processes

Lecture Objectives

• Identify organs involved in fetal hematopoiesis
• Detail the stages of hematopoiesis throughout development (prenatal and postnatal)
• Understand the steps of post-natal blood cell formation (erythropoiesis, granulopoiesis, monocytopoiesis, megakaryopoiesis)

Hematopoiesis (Hemopoiesis)

• Negative feedback regulates RBC and platelet count
• Immune response influences WBC type abundance
• Red bone marrow is the primary site for hematopoiesis
• Pluripotent stem cells differentiate into many cell types

Sites of Hematopoiesis

• Embryonic hematopoiesis starts in the yolk sac, followed by the liver, then the spleen
• By the fourth and fifth month, the marrow cavity becomes the primary site for granulocytes and platelets
• By the seventh month, the bone marrow is primarily responsible for the formation of erythrocytes (RBCs)
• After birth, the bone marrow is primarily responsible, with some involvement from the spleen and liver
• In adulthood, active hematopoietic sites are primarily in the bone marrow of the skull, ribs, sternum, vertebral column, pelvis, and proximal ends of the femurs

Hematopoiesis Details

• Hematopoiesis is the process of immature precursor cells becoming mature blood cells
• A single pluripotent stem cell produces all mature blood cell types
• The image shows a schematic illustrating the development of committed progenitor cells into various mature blood cells

Bone Marrow Types

• Two types exist: red and yellow
• Red bone marrow contains blood and blood-forming cells, providing blood cells
• Yellow bone marrow contains a high proportion of adipose cells

Red Bone Marrow Structure

• Stroma: a network of reticular cells and fibers (type I and III collagen, fibronectin, laminin, and hemonectin) supporting hematopoietic cells
• Hematopoietic cords: areas in the marrow containing blood cells
• Sinusoidal capillaries: specialized capillaries in the marrow, facilitating blood cell passage

Erythropoiesis

• The process of forming erythrocytes and hemoglobin synthesis
• Cell size and organelles change during maturation
• The nucleus disappears, and hemoglobin takes over
• Maturation takes about 7 days

Erythropoiesis Stages

• Proerythroblast: the first recognizable cell with loose chromatin
• Differentiating basophilic to orthochromatophilic, the nucleus condenses, disappears
• Reticulocytes are released from bone marrow into blood; they mature into erythrocytes in spleen
• Erythrocytes lack nuclei, are biconcave, and contain hemoglobin

Leukopoiesis

• Myeloblast, promyelocyte, myelocyte are capable of division
• Maturation of metamyelocyte and band cells reduces cell size

Granulopoiesis

• Involves protein synthesis in granules for maturation
• Early stage involves azurophilic granules for lysosomal enzymes
• Later stages develop specific granules depending on granulocyte type

Lymphocyte Maturation

• Lymphocytes originate in lymphoid organs and bone marrow
• Lymphoblasts are early progenitor cells, typically large.
• Lymphocytes eventually develop into smaller, more condensed chromatin cells.

Monocyte Maturation

• Monoblasts appear like myeloblasts are committed progenitors
• Develop into large cells with slightly indented nuclei
• Monocytes in the blood will mature to tissue macrophages or dendritic cells when activated

Megakaryopoiesis

• Megakaryoblasts are precursors of platelets
• Cells produce many nuclei without dividing (increasing cell size) which differentiates in morphology from other cells.
• Cytoplasm is filled with organelles that mature to become platelets via fragmentation. Platelets are components of the blood.

Explore the fascinating process of hematopoiesis, or blood cell formation, as outlined by Prof. Dr. Siti Balkis Budin. This quiz covers the stages of fetal and postnatal hematopoiesis, the functions of different blood cells, and the organs involved in this critical biological process.