Erythrocytes and Hematopoiesis Quiz

Erythrocytes (Red Blood Cells)

• Erythrocytes are specialized blood cells, highly numerous, transporting oxygen (O2) from the lungs to tissues and carbon dioxide (CO2) from tissues to lungs.
• Mature RBCs lack nuclei and cytoplasmic organelles.
• Red blood cell structure is characterized by its biconcave disc shape, with diameter of 7-8 µm and volume of 80-100 femtoliters (fl). This enables flexibility to pass through small blood vessels
• RBCs have a life span of 3-4 months (~120 days).

Hematopoiesis (RBC Production)

• The yolk sac is the initial site of RBC generation.
• By week 8, the liver becomes the exclusive source of RBCs until the 18th week of gestation.
• Afterward, the spleen, followed by the bone marrow, take over as the primary sites of RBC generation in adults.
• The adult bone marrow remains the sole site for RBC generation. An astounding 3 x 10⁵ erythrocytes are generated each second in a 70-kg adult.
• Development of mature RBC from pluripotent stem cells involves stages like BFU-E, CFU-E, pro-normoblast, basophilic erythroblast, polychromatic erythroblast, orthochromatic erythroblast, reticulocyte, and finally mature red blood cell.

Erythropoietin

• Erythropoietin (EPO) is a hormone responsible for the regulation of erythropoiesis.
• EPO is released in response to decreased hemoglobin (Hb) levels, primarily produced in the kidney.
• It travels to the bone marrow and promotes the production of erythroid stem cells.
• Increased EPO leads to an increase in erythroid cell line production.

RBC Indices

• RBC count: measurement of red blood cells. Normal range is different for males and females.

• Erythrocyte Sedimentation Rate (ESR): rate at which red blood cells settle in a sample of blood. Factors influencing its rate include plasma proteins, bile pigments, and pathological conditions.

• Hematocrit (Hct): percentage of whole blood occupied by red blood cells. Typical ranges are 42-52% for males and 37-48% for females

• Mean Corpuscular Volume (MCV): average volume of red blood cells. The normal range is 80-95 fL.

• Mean Corpuscular Hemoglobin (MCH): average weight of hemoglobin within a red blood cell, measured in picograms (pg). Normal range is 27–32 pg.

• Mean Corpuscular Hemoglobin Concentration (MCHC): concentration of hemoglobin within a red blood cell, measured in grams per deciliter (g/dL). Normal range is approximately 32–36 g/dL.

• Color Index (CI): the ratio of the percentage of hemoglobin and the percentage of the red blood cells. Normal range is 0.8-1.2.

• Reticulocyte count: measure of the number of young red blood cells in the circulating blood, representing the rate of red blood cell production. Typically 0.5-1.5% (50-100x10⁹/L).

• Red Cell Distribution Width (RDW): measures variation in red blood cell size (anisocytosis) Normal range is 10.2-14.5%.

Hemoglobin (Hb)

• Hb is the most abundant protein in red blood cells, responsible for carrying oxygen.
• Hb is a tetramer, composed of four heme groups and four polypeptide chains (globins) and a critical iron-containing component that enables O₂ binding and release.
• 1 g of Hb binds to 1.34 mL of O2.
• Different forms of Hb exist, including HbA, HbF and abnormal Hb forms (due to mutations).
• Conditions like thalassemia and sickle cell disease are associated with abnormal Hb production.
• A single amino acid change can drastically alter the properties of Hb.

Hemoglobinopathies

• Disorders categorized by abnormal Hb forms
• Sickle cell disease: a genetic disorder characterized by abnormal Hb causing RBCs to assume a sickle shape. This can cause blockages in blood vessels due to the unique ability of deoxygenated Hb to form an aggregated fibrillar structure.
• Thalassemia: a group of inherited blood disorders with reduced Hb production.

RBC Functions

• Transport Function: carrying crucial substances like oxygen, carbon dioxide, nutrients and hormones to different parts of the body.
• Protective function: participate in immune reactions due to the presence of specific glycoproteins and lipids.
• Regulatory function: maintaining acid-base balance – the iron carrying capabilities of hemoglobin bind carbon dioxide effectively reducing the content of H₂CO₃(carbonic acid) in blood.

Abnormal Increase and Decrease in RBC Count

• Polycythemia (Erythrocytosis): elevated RBC count beyond normal range.
• Anemia (Erythrocytopenia): reduced RBC count well below the normal range.

Other Oxygen-carrying Proteins

• Myoglobin: protein found in muscle tissue.
• Neuroglobin and cytoglobin: proteins found in nerve tissue and various other tissues, respectively.

Assignment

• Create a well-labeled diagram, outlining hematopoietic pathways.
• Briefly discuss the hemoglobinization process from pluripotent stem cells to erythrocytes.

Test your knowledge on erythrocytes, the vital red blood cells responsible for oxygen transport, and their production process known as hematopoiesis. This quiz covers the structure, lifespan, and generation sites of RBCs throughout development and adulthood.