Overview
This lecture covers the formation, characteristics, and functions of blood's formed elements—red blood cells, white blood cells, and platelets—as well as the processes of hematopoiesis and erythropoiesis.
Red Blood Cells (RBCs)
- RBCs (erythrocytes) transport oxygen from lungs to cells and carbon dioxide from cells to lungs.
- Mature RBCs have a biconcave shape, lack a nucleus and mitochondria, maximizing space for hemoglobin.
- The biconcave shape increases surface area for gas diffusion and allows cell deformability for capillary passage.
- RBCs are key in bicarbonate buffering via carbonic anhydrase, aiding COâ‚‚ transport as bicarbonate.
White Blood Cells (WBCs)
- WBCs (leukocytes) are immune cells that defend against pathogens and toxins.
- WBCs retain nuclei and organelles and are less numerous than RBCs.
- Various WBC types exist, each with specific immune roles.
Platelets
- Platelets (thrombocytes) are cell fragments involved in blood clotting and vessel repair.
- Platelets release PDGF, promoting blood vessel formation and healing.
- Produced by megakaryocytes in bone marrow.
Hematopoiesis
- Hematopoiesis is the continuous process of forming new blood cells and platelets in red bone marrow.
- Hematopoietic stem cells (HSCs) are undifferentiated cells that can become any blood cell type.
- Myeloid cell line produces RBCs, platelets, and several WBC types (neutrophils, eosinophils, basophils, monocytes, mast cells).
- Lymphoid cell line produces lymphocytes (B cells, T cells, natural killer cells).
- Hematopoiesis is regulated by cytokines, including colony-stimulating factors and thrombopoietin.
Erythropoiesis (Red Blood Cell Formation)
- Erythropoiesis is the specific process of creating new RBCs from myeloid stem cells.
- This process takes about a week, with the nucleus ejected near the end to form mature RBCs.
- Erythropoietin (EPO), produced primarily by the kidneys during low oxygen, controls erythropoiesis.
- RBC production requires iron (for hemoglobin), vitamin B9 (folate), and vitamin B12 (for DNA synthesis).
Hemoglobin & Oxygen Transport
- Hemoglobin is an iron-containing protein in RBCs responsible for 98–99% of blood's oxygen transport.
- Each hemoglobin molecule has four globin chains and four heme groups; each heme binds one oxygen molecule.
- Oxygen binding to hemoglobin increases its affinity for more oxygen (cooperative binding).
- Adult hemoglobin typically consists of two alpha and two beta chains.
Key Terms & Definitions
- Erythrocyte (RBC) — red blood cell, transports oxygen and carbon dioxide.
- Leukocyte (WBC) — white blood cell, provides immune defense.
- Platelet (Thrombocyte) — cell fragment involved in blood clotting.
- Hematopoiesis — formation of all blood cells.
- Erythropoiesis — formation of new red blood cells.
- Hemoglobin — iron-containing protein in RBCs that binds oxygen.
- Erythropoietin (EPO) — hormone that stimulates RBC production.
- Cytokine — signaling molecule that regulates cell activity.
Action Items / Next Steps
- Review the roles and characteristics of formed elements in the blood.
- Study the steps and regulation of hematopoiesis and erythropoiesis.
- Read ahead on details of the immune system and cardiovascular physiology.