Lecture 2 Red Blood Cells, Anemias & Polycythemias 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Objectives By the end of this lecture the student should be able to: Describe the functions of red blood cells. State the requirements for RBC production. Describe the regulation of RBC production. Define anaemia. Classify anaemias according to cause. Classify anaemias according to red cell size. Define polycythemia. Describe different types of polycythemias and their causes. Describe the hemodynamic effects of anaemia and polycythemia. 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Red Blood Cells Shape: biconcave disc Size: 7 m in diameter, 2 m thick Count: men 5.4 million/mm3 women 4.8 million /mm3 Hemoglobin concentration: men 16 ± 2 g/dl women 14 ± 2 g/dl 2nd year Medicine- IBLS Module May 2008

What are the functions of RBCs 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Functions of RBC Transport hemoglobin (Hb) which carries O2. Contain carbonic anhydrase enzyme (CO2 transport in the form of bicarbonate ion). Hb is an acid-base buffer. RBC are important for normal blood viscosity. 2nd year Medicine- IBLS Module May 2008

Requirements for effective erythropoiesis Healthy bone marrow Metals: iron, cobalt Vitamins: B12 and folic acid, vit C Hormones: androgens, thyroxine Healthy kidney: erythropoietin. Healthy liver: Formation of globin part of Hb. Storage of vit. B12, iron Formation of 10-15% of erythropoietin 2nd year Medicine- IBLS Module May 2008 6

Control of RBC production (Erythropoiesis) Any condition that causes the quantity of O2 transported to the tissue to decrease (tissue hypoxia), increases the rate of RBC production. 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Anemia Definition: a low hemoglobin (Hb) level for age and sex. adult males: <14 g/dl adult females: < 12 g/dl 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Blood Loss Anemia Acute: after rapid hemorrhage, plasma portion is replaced in 1-3 days→ ↓ RBC concentration. Chronic blood loss: Not enough Fe is absorbed from intestines to form hemoglobin as rapidly as it is lost. 2nd year Medicine- IBLS Module May 2008

Chemicals, drugs, viruses Aplastic Anemia Aplastic anemia Primary Congenital Acquired Secondary Chemicals, drugs, viruses Ionizing radiation, Decrease bone marrow function 2nd year Medicine- IBLS Module May 2008

Immune (transfusion reactions), infection (malaria), drugs Hemolytic Anemia Hemolytic Anemia Hereditary Membrane (e.g. sherocytosis) Metabolism (e.g. G6PD deficiency) Hemoglobin (e.g. sickle cell) Acquired Immune (transfusion reactions), infection (malaria), drugs

2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Megaloblastic anemia Slow reproduction of erythroblasts due to vitamin B12 or folic acid deficiency (defective DNA synthesis-maturation failure). Causes of vitamin B12 deficiency: Nutritional: especially vegans. Malabsorption (Gastric or intestinal causes): Pernicious anemia: due to intrinsic factor deficiency in patients with autoimmune atrophic gastritis. Total or partial gastrectomy Small intestinal lesions. 2nd year Medicine- IBLS Module May 2008

Hemodynamic effects of anemia ↑ cardiac output and pumping workload on the heart due to: ↓ blood viscosity → ↓ peripheral resistance Hypoxia → vasodilation of arterioles → ↑ V.R. to heart 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Polycythemia Definition: an increase in the Hb concentration above the upper limit of normal for the patient’s age and sex. 2nd year Medicine- IBLS Module May 2008

Polycythemia (rubra) vera (↑ Red cell mass) Absolute Polycythemia (rubra) vera Primary Secondary (Normal red cell mass) Relative ↓ Plasma volume 2nd year Medicine- IBLS Module May 2008

Absolute Polycythemia Secondary Compansatory erythropoietin increase Physiological e.g. High altitude Pathological e.g. Cardiac and pulmonary diseases Inappropriate erythropoietin increase e.g. tumors secreting erythropietin 2nd year Medicine- IBLS Module May 2008

Hemodynamic effects of polycythemia ↑ viscosity → sluggish blood flow. ↑ blood volume → increase venous return. Hypertension in 1/3 of patients. 2nd year Medicine- IBLS Module May 2008

2nd year Medicine- IBLS Module May 2008 Summary What are the main functions of RBCs? What is the main stimulus for increased RBC formation? What are the main requirements for effective erythropoiesis? Define anemia and polycythemia and list their different causes. What are the circulatory consequences of anemia and polycythemia? 2nd year Medicine- IBLS Module May 2008