Erythrocytes (RBCs)

• Erythrocytes, also known as RBCs, are the main topic, covering erythropoiesis and anemia. The presentation is by Professor Dr. Faten Mahmoud A. Diab, a professor of medical physiology from Egypt, from the College of Dentistry.
• The learning objectives include describing the structure and function of erythrocytes, defining erythropoiesis, and describing the regulation of erythropoiesis.

Blood components

• Blood components include plasma, erythrocytes (RBCs), leukocytes (WBCs), and platelets.
• Most formed elements in the bloodstream survive only for a few days.
• Erythrocytes normally constitute about 45% of the total volume of a blood sample. This percentage is known as the hematocrit value or packed cell volume (PCV).
• Normal hematocrit levels show the PCV in men ranges from 38% to 48%, while in women, the PCV typically ranges from 35% to 45%.

Erythrocytes

• Erythrocytes, or RBCs, are small corpuscles, not cells, shaped like a biconcave disc, with a diameter of 7.5 µm. They act as "bags" for hemoglobin (Hb).
• The biconcave shape of RBCs allows for flexibility, shape change while squeezing through capillaries, and increases the surface area for gas diffusion.

RBC Count

• Normal RBC count ranges from 4.7 to 6.1 million cells/µl or (mm³) in men and 4.2 to 5.4 million cells/mm³ in women; they have an average of 5 million/mm3.
• RBCs transport respiratory gases such as oxygen and carbon dioxide by the hemoglobin inside.
• Hemoglobin in RBCs functions as an excellent acid-base buffer, responsible for most of the acid-base buffering power of whole blood (pH regulation).
• Deoxyhemoglobin, a reduced hemoglobin in dark red, occurs in the tissues and is transported from tissues to lungs.
• Oxygen diffuses from the air of the lungs into the blood and then into the erythrocytes, binding to hemoglobin to form oxyhemoglobin.
• Hemoglobin A, the most common form of hemoglobin in adult humans, is a combination of two alpha chains (2α) and two beta (2β) chains.
• Each hemoglobin molecule can transport four molecules of oxygen because each iron atom can combine reversibly with one molecule of oxygen.
• Normal hemoglobin values are 13-18 grams per 100 milliliters of blood (g/100 ml) (g%) in adult males and 12-16 g/100 ml in adult females, with an average of 15 g/100 ml.
• Males have more RBCs, PCV, and hemoglobin (Hb) than females because males have testosterone which enhances the kidneys' production of erythropoietin, leading to more RBC production.
• Females are subjected to more blood loss due to menstruation and delivery.

Hematopoiesis

• Hematopoiesis in the bone marrow leads to erythropoiesis, leukopoiesis, and thrombopoiesis.

Erythropoiesis

• Erythropoiesis is the formation of RBCs.
• During intrauterine fetal life, it occurs 0-2 months in the yolk sac, 2-7 months in the liver and spleen, and 5-9 months in the bone marrow.
• In infants and children blood cells are formed in the all-bone marrow cavities of most all bones.
• In adults, it occurs only in the red bone marrow of the sternum (breastbone), vertebrae (backbone), ribs, the base of the skull, and upper ends of long limb bones.
• It is defined as stimulated by a decrease in RBC count and is subjected to negative feedback control.

Factors controlling erythropoiesis

• Tissue oxygenation and erythropoietin hormone stimulates it.
• Erythropoietin hormone is secreted 85% from kidneys and 15% from the liver and is mainly stimulated by tissue hypoxia due to hemorrhage, high altitude, heart failure, anemia, and lung disease.
• Nutritional requirements for erythropoiesis include protein of high biological value to form polypeptide chains of Hb and iron is essential for Hb synthesis, as it is a constituent of the heme molecule.
• Vitamins such as vitamin B12 and folic acid serve as maturation factors.
• It needs healthy bone marrow and liver.
• It is controlled by other hormones, including testosterone, thyroid hormones, growth hormones, and cortisol.
• Other factors such as Vitamin C, trace elements like cobalt and zinc and copper, and alkalosis also have an influence
• Red blood cells have a useful lifespan of approximately 120 days.
• As erythrocytes age, they lose flexibility, become increasingly rigid and fragile, and their hemoglobin begins to degenerate.
• Old erythrocytes become trapped and fragmented in smaller capillaries, especially in the spleen and liver; for this reason, the spleen is sometimes called the "red blood cell graveyard."

RBC Disorders

• RBC disorders include anemia and polycythemia.