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

2. 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

3. 2nd year Medicine- IBLS Module May 2008
Red Blood Cells
Shape: biconcave disc
Size: 7 m in diameter, 2 m thick
Count:
men million/mm3
women 4.8 million /mm3
Hemoglobin concentration:
men ± 2 g/dl
women 14 ± 2 g/dl
2nd year Medicine- IBLS Module May 2008

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

5. 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

6. 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

7. 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

8. 2nd year Medicine- IBLS Module May 2008

9. 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

10. 2nd year Medicine- IBLS Module May 2008

11. 2nd year Medicine- IBLS Module May 2008

12. 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

13. 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

14. 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

15. 2nd year Medicine- IBLS Module May 2008

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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