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

2nd year Medicine- IBLS Module May 2008

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Lecture 2Red Blood Cells, Anemias &

Polycythemias


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ObjectivesBy the end of this lecture the student should be able to:

1. Describe the functions of red blood cells.2. State the requirements for RBC production.3. Describe the regulation of RBC production.4. Define anaemia.5. Classify anaemias according to cause.6. Classify anaemias according to red cell size.7. Define polycythemia.8. Describe different types of polycythemias and their causes.9. Describe the hemodynamic effects of anaemia and

polycythemia.


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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


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What are the functions of RBCs


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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.


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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


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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.


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Anemia

• Definition:

–a low hemoglobin (Hb) level for age and sex.

– adult males: <14 g/dl

– adult females: < 12 g/dl


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Classification

According to cause According to cell size


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Anaemia according to cause

Blood loss Bone marrow failureDestruction of red cells

)Haemolytic(

Acute Chronic Nutritional Aplastic Hereditary Acquired


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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.


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Aplastic Anemia

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Hemolytic Anemia


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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.

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


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Polycythemia

Definition:

an increase in the Hb concentration above the upper limit of normal for the patient’s age and sex.


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Absolute Polycythemia


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Hemodynamic effects of polycythemia

• ↑ viscosity → sluggish blood flow.

• ↑ blood volume → increase venous return.

• Hypertension in 1/3 of patients.


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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?

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