Physiology of Red Blood Cells (RBCs) Erythrocytes Structural characteristics Hemoglobin Erythropoiesis Erythrocytes destruction Anemia Polycythemia

Filled with hemoglobin Shape and Size of Red Blood Cells. 1 µm No nucleus (anucleate) or organelles (no mitochondria, no endoplasmic reticulum) biconcave discs having a mean diameter of about 7.8 micrometers and a thickness of 2.5 micrometers at the thickest point and 1 micrometer or less in the center. The average volume (MCV) of the red blood cell is 90 to 95 cubic micrometers (fL). 7.8 The red blood cell is a “bag” that can be deformed into almost any shape Life Span of Red Blood Cells is About 120 Days Filled with hemoglobin Concentration of Red Blood Cells in the Blood Men 5,200,000 (±300,000); women, it is 4,700,000 (±300,000)

Red Blood Cells Function O2 transport CO2 transport Buffer

RBCs concentrate Hb in their cytoplasm Quantity of Hemoglobin Hb in the Cells. RBCs concentrate Hb in their cytoplasm Each 100 ml of RBCs , the concentration of Hb is about 34g (MCHC) This is the maximum metabolic limit and normal people always Hb near the maximum value If hematocrit (Hct) is normal, then Hb is one third of Hct value Hct =45% then Hb = 15 Each gram of Hb can bind 1,34 ml of O2 So 100 ml of blood carry 20 ml of O2 in man Women the amount is less.

Production of Red Blood Cells Erythropoiesis

Production of RBC Early few weeks of embryo nucleated RBCs are formed in yolk sac. Middle trimester mainly in liver & spleen & lymph nodes. Last months RBCs are formed in bone marrow of all bones Bone marrow of flat bone continue to produce RBC into adult life Shaft of long bone stop to produce RBC at puberty while epiphysis continued

Production of RBC

Genesis of RBC All blood cell are formed from Pluripotential hematopoietic stem cells  committed cells: Committed stem cells for RBC Committed stem cells for WBC Growth of different stems cells are controlled by different growth factors

Stages of Differentiation of Red Blood Cells The first cell that can be identified as belonging to the red blood cell series is the proerythroblast The first-generation cells are called basophil erythroblasts, very little hemoglobin At the satge of reticulocytes, the nucleus condenses to a small size, and its final remnant is absorbed or extruded from the cell. At the same time, the endoplasmic reticulum is also reabsorbed Reticulocytes pass from bone marrow into blood capillaries by diapedesis In the blood stream the remaining basophilic material will disappear in 1-2 days and mature erythrocytes will developed

Formation of Hemoglobin Red Blood Cells (cont.) Formation of Hemoglobin Fig. 32.5 Formation of hemoglobin Fig. 32.6 Basic structure of hemoglobin

About 300 million molecules of HB in every red cell. Each molecule of HB carries 4 oxygen O2 molecules. Normal values: Females: 14 g/100ml blood Males: 15 g/100 ml blood Oxygenated Hemoglobin Bright Red (systemic) *Deoxygenated Hemoglobin dull (venous circulation)

Regulation of RBC production Erythropoiesis is stimulated by erythropoietin hormone produced by the kidney in response to hypoxia (low oxygen in the blood) Hypoxia caused by: Low RBC count (Anaemia) Hemorrhage High altitude Prolong heart failure Lung disease

Tissue oxygenation and RBC formation

Erythropoietin Glycoprotein 90% from renal cortex 10% liver Stimulate the growth of early stem cells Does not affect maturation process Can be measured in plasma & urine High levels of erythropoietin anemia High altitude Heart failure Lung Disease (Result in polycythemia)

maintain pliability of the cell membrane, Life Span of Red Blood Cells is About 120 Days RBCs contain cytoplasmic enzymes that are very important for: metabolizing glucose and forming small amounts of ATP. These enzymes also maintain pliability of the cell membrane, (2) maintain membrane transport of ions, (3) keep the iron of the cells’ hemoglobin in the ferrous form rather than ferric form, and (4) prevent oxidation of the proteins in the red cells.

Destruction of RBCs take place in macrophages of the: Spleen Liver Lymph nodes urobilinogen

Anemias 1. Blood Loss Anemia. 2. Aplastic Anemia. 3. Megaloblastic Anemia. 4. Hemolytic Anemia. Effects of Anemia on Function of the Circulatory System Viscosity, resistance and cardiac output Exercise

Polycythemia Secondary Polycythemia. red cell count commonly rises to 6 to 7 million/mm3, about 30 percent above normal. physiologic polycythemia Polycythemia Vera (Erythremia) Effect of Polycythemia on Function of the Circulatory System Viscosity,