RED BLOOD CELLS PHYSIOLOGY vvvvvvvvv.pptx

physiology

1. Blood

2. Composition of Blood Blood is the body’s only fluid tissue It is composed of liquid plasma and formed elements Formed elements include: Erythrocytes , or red blood cells (RBCs) Leukocytes , or white blood cells (WBCs) Platelets Hematocrit – the percentage of RBCs out of the total blood volume

3. 1) Erythrocytes (RBCs) Biconcave discs, anucleated, essentially no organelles Filled with about 60% water and 34% hemoglobin (Hb) , a protein that functions in gas transport ATP is generated anaerobically , so the erythrocytes do not consume the oxygen they transport Contain the plasma membrane protein spectrin and other proteins that: Give erythrocytes their flexibility Allow them to change shape as necessary

4. 1) Erythrocytes (Continued): Function RBCs are dedicated to respiratory gas transport Hb reversibly binds with oxygen Most oxygen in the blood is bound to Hb Hb is composed of the protein globin, made up of 2 alpha & 2 beta chains , each bound to a heme group Each heme group bears an atom of iron (Fe) , which can bind to one oxygen molecule Each Hb molecule can transport four molecules of oxygen

5. 1) Erythrocytes (continued): Production Hematopoiesis – blood cell formation Hematopoiesis occurs in the red bone marrow of the: Axial skeleton and girdles Epiphyses of the humerus and femur Hemocytoblasts give rise to all formed elements Specifically, production of erythrocytes: erythropoiesis

6. 1) Erythrocytes (continued): Erythropoiesis A h emocytoblast (the stem cell that gives rise to all of the formed elements) is transformed into A p roerythroblast, which develops into An early e rythroblast, which is characterized by the ribosome synthesis phase A late erythroblast is characterized by Hb accumulation A normoblast continues the Hb accumulation phase. Ejection of the nucleus leads to A reticulocyte which matures into An erythrocyte

7. Erythrocytes (continued): Regulation and Requirements for Erythropoiesis Circulating erythrocytes – the number remains constant and reflects a balance between RBC production and destruction Too few RBCs leads to tissue hypoxia Too many RBCs causes undesirable blood viscosity Erythropoiesis is hormonally controlled and depends on adequate supplies of iron , amino acids , and B vitamins Intracellular iron is stored in protein-iron complexes such as ferritin and hemosiderin Circulating iron is loosely bound to the transport protein transferrin Erythropoietin (EPO) release by the kidneys is triggered by: Hypoxia due to decreased RBCs Decreased oxygen availability Increased tissue demand for oxygen

8. 1) Erythrocytes (continued): Erythropoietin Mechanism Homeostasis: Normal blood oxygen levels Increases O 2 -carrying ability of blood Erythropoietin stimulates red bone marrow Reduces O 2 levels in blood Kidney (and liver to a smaller extent) releases erythropoietin Enhanced erythropoiesis increases RBC count Stimulus: Hypoxia due to decreased RBC count, decreased amount of hemoglobin, or decreased availability of O 2 Start Imbalance Imbalance Figure 17.6

9. 1) Erythrocytes (continued): Life and death of Erythrocytes The life span of an erythrocyte is approximately 120 days Old RBCs get rigid & fragile, and Hb begins to degenerate Dying RBCs are engulfed by macrophages Heme and globin are separated and the iron is salvaged Heme is degraded to a yellow pigment called bilirubin The liver secretes bilirubin into the intestines as bile The intestines metabolize it into urobilinogen This degraded pigment leaves the body in feces, in a pigment called stercobilin Globin (polypeptide chains) is metabolized into amino acids and is released into the circulation Hb released into the blood is captured by haptoglobin and phagocytized

10. Hemoglobin Amino acids Globin Raw materials are made available in blood for erythrocyte synthesis. Iron is bound to transferrin and released to blood from liver as needed for erythropoiesis Food nutrients, including amino acids, Fe, B 12 , and folic acid are absorbed from intestine and enter blood Heme Circulation Iron stored as ferritin, hemosiderin Bilirubin Bilirubin is picked up from blood by liver, secreted into intestine in bile, metabolized to stercobilin by bacteria and excreted in feces Erythropoietin levels rise in blood. Erythropoietin and necessary raw materials in blood promote erythropoiesis in red bone marrow. New erythrocytes enter bloodstream; function about 120 days. Low O 2 levels in blood stimulate kidneys to produce erythropoietin. Aged and damaged red blood cells are engulfed by macrophages of liver, spleen, and bone marrow; the hemoglobin is broken down. 1 2 3 4 5 6 Figure 17.7 Life and Death of Erythrocytes

11. Anemia – blood has abnormally low oxygen-carrying capacity It is a symptom rather than a disease itself Blood oxygen levels cannot support normal metabolism Signs/symptoms include: fatigue, paleness, shortness of breath, and chills Types Hemorrhagic anemia – result of loss of blood Hemolytic anemia – prematurely ruptured RBCs Aplastic anemia – destruction/inhibition of red bone marrow Iron-deficiency anemia results from lack of iron Pernicious anemia results from either deficiency of vitamin B 12 or lack of intrinsic factor needed for absorption of B 12 Treatment is intramuscular injection of B 12 Thalassemias – absent or faulty globin chain in Hb Sickle-cell anemia – results from a defective gene & causes RBCs to become sickle-shaped in low oxygen situations 1) Erythrocytes (continued): Disorders

12. Erythrocytes (continued): Disorders - Polycythemia Polycythemia – excess RBCs increase blood viscosity Three main polycythemias are: Polycythemia vera , bone marrow cancer Secondary polycythemia , low levels of oxygen or EPO increases Blood doping , results in enhanced endurance and speed.