Lecture 5a: Pathophysiology of Anaemias and Polycythemia

There are essentially three reasons why an anaemia (lack of RBC’s) occurs:

1. rapid loss of RBC’s
2. a deficiency in the RBC’s
3. a too slow or no production of RBC’s.

1.

Acute bleeding: In that situation, plasma is replaced in 1-3 days (hematocrit decreases!) while RBC’s are replaced (by the bone marrow) in 3-4 weeks.

2.

Chronic bleeding: This will often cause a lack of iron. Then the hemoglobine concentration in the RBC will decrease => microcytic (small) hypochromic (light color) anemia.

3.

Chronic bleeding is often caused by a small seeping wound in the gastrointestinal system (ulcer) or, in females, due to excessive menstruation.

1.

Bone marrow aplasia (not enough functioning bone marrow).

2.

caused by excessive radiation, X-ray treatments (CT-scans!), drugs, chemotherapy.

3.

or nuclear disasters such as Chernobyl (remember?).

1.

Deficiency in intrinsic factor ( = pernicious anaemia), or vitamin B12 and/or folic acid.

2.

Causes slow RBC production => too large, odd shaped cells => megaloblasts => fragile, short life span.

1.

These anaemia’s are caused by abnormal RBC (many hereditary), and short life span, such as:

2.

Hereditary Spherocytosis: spherical and small

3.

Sickle Cell anaemia: HbS (formation of crystal cells in hypoxia). Cave: sickle cell crisis!

4.

Erythroblastosis Foetalis: Rhesus+ fetal RBC’s attacked by antibodies from Rh- mother.

5.

Thalassaemias. The most common thalassaemias have abnormal or deficient beta-globuline chains. Major problem here is iron overload due to repeated transfusions.

6.

Inherited enzyme deficiencies G6PD deficiencies is the most common, X-chromosome linked type. Upon oxidative stress hemoglobine is changed into met-hemoglobine which does not bind oxygen.

But there are also other classification possible, such as:

1. Microcytic anaemia (low MCV)
2. Macrocytic anaemia (high MVC)
3. Normocytic anaemia (normal MCV)

1.

Physiological Polycythemia (high altitude for example).

2.

Secundary Polycythemia: due to cardiac or pulmonary problems

3.

Polycythemia Vera: (“true” polycythemia) due to cancer in the bone marrow

4.

Doping: autotransfusion. About one month before the competition, you bleed a vein and store one litre of your blood in the fridge. The body will detect this loss of blood and make new RBC’s. A few days before the competition, you take out the blood in the fridge and infuse it back into your circulation. Great; you now have more RBC’s then the competition!

5.

Doping: EPO EPO is shorthand for artifical erythropoietin. This hormone is important for patients that do not make enough erythropoietin; kidney patients for example. But in competition, you can also inject EPO in a normal person to increase the RBC’s to higher levels. This is for example very popular in sports as cycling (Tour de France!), marathon etc where the body has to work very hard and where you want to WIN!

1.

In both cases, the problem is the same; the heart has to work much

2.

In the case of anaemia, the heart will pump harder and faster to circulate the blood, with its smaller amount of RBC’s and haemoglobin, faster around the circulation to get more oxygen to the working tissues.

3.

In the case of polycythemia, the viscosity of the blood has increased. Therefore, it is more difficult for blood to flow through the arteries, veins and capillaries. Therefore, the blood pressure has to increase to push the blood through the circulation and this means that the heart must work harder.

4.

Therefore, the symptoms in both anaemia and polycythemia are similar and are:

a) increase heart rate (tachycardia)

b) stronger heart contractions (palpitations)

c) if chronic => cardiomegaly (big heart)

d) finally; heart failure, death