Overview
This lecture explains the structure, function, and life cycle of red blood cells (erythrocytes), how their levels are regulated, and the science and dangers behind blood doping in sports.
Blood Doping and Erythrocytes
- Blood doping involves artificially increasing red blood cell (RBC) count to enhance athletic performance.
- RBCs (erythrocytes) make up about 45% of blood volume and transport oxygen and carbon dioxide.
- Their biconcave shape increases surface area for gas exchange and enhances flexibility in small vessels.
- RBCs lack a nucleus and most organelles, living about 120 days due to membrane wear and limited repair ability.
Hemoglobin: Function and Structure
- RBCs are 97% hemoglobin (by dry weight), a protein that binds and transports oxygen efficiently.
- Hemoglobin consists of four globin proteins, each with an iron-containing heme group that binds oxygen.
- Each RBC contains about 250 million hemoglobin molecules, each binding four oxygen molecules, totaling about a billion oxygen molecules per cell.
- Free hemoglobin in blood is dangerous because it thickens blood and impedes flow.
Erythrocyte Formation and Regulation
- RBCs are produced in red bone marrow through hematopoiesis, beginning as hemocytoblasts (stem cells).
- Developing erythroblasts produce hemoglobin and lose organelles, becoming reticulocytes before maturing into erythrocytes.
- Erythropoietin (EPO), a hormone mainly produced by kidneys, stimulates RBC production when oxygen levels drop.
- EPO regulation uses hypoxia-inducible factor, which monitors blood oxygen and triggers EPO release if low.
Erythrocyte Life Cycle and Breakdown
- Old and damaged RBCs are removed by macrophages, primarily in the spleen ("RBC graveyard"), liver, and bone marrow.
- Hemoglobin is broken down: globin becomes amino acids, iron is stored or reused, and heme is converted to bilirubin and excreted.
Blood Doping Risks
- Doping methods include injecting EPO or re-infusing stored blood to increase RBC count and oxygen delivery.
- Excessive RBCs thicken blood, making it harder to pump and increasing risks of clots, stroke, and heart failure.
- Blood doping is banned and considered cheating in sports.
Key Terms & Definitions
- Erythrocyte (Red Blood Cell) — cell responsible for carrying oxygen and carbon dioxide in blood.
- Hemoglobin — protein in RBCs that binds and transports oxygen.
- Hematopoiesis — process of blood cell formation in bone marrow.
- Erythropoietin (EPO) — hormone that stimulates red blood cell production.
- Hypoxia — condition of insufficient oxygen in tissues.
- Reticulocyte — immature red blood cell with residual ribosomes.
- Bilirubin — yellow pigment from heme breakdown, excreted in bile.
Action Items / Next Steps
- Review oxygen transport mechanisms and details of the respiratory system for deeper understanding.
- Prepare for discussion or assessment on blood cell formation and regulation.
- Read about the ethical and health implications of doping in sports.