Polycythaemia vera: affects circulatory system function

2021-05-07 11:37 PM

In polycythaemia vera, the amount of blood in this plexus is greatly increased. Furthermore, since blood flows slowly through the skin capillaries before entering the venous plexus, a larger amount of reduced haemoglobin is required.

Due to the greatly increased viscosity in polycythaemia vera, peripheral blood circulation is usually very slow. Consistent with the law of the factors that regulate blood return to the heart, as discussed in chapter 20, increasing blood viscosity lowers venous blood return to the heart. In contrast, the greatly increased blood volume in polycythaemia vera tends to increase venous blood return. In fact, the cardiac output in polycythaemia vera does not deviate much from normal because the two factors more or less neutralize each other. Arterial pressure is also normal in most people with polycythaemia vera, although there is about a third of increased arterial pressure. This means that blood pressure regulation can often compensate for the tendency to increase blood viscosity, increase peripheral resistance and, therefore, increase arterial pressure.

However, beyond certain limits, these mechanisms are ineffective and high blood pressure occurs. Skin colour is highly dependent on the amount of blood in the subcutaneous venous-venous plexus. In polycythaemia vera, the amount of blood in this plexus is greatly increased. Furthermore, since blood flows slowly through the skin capillaries before entering the venous plexus, a larger amount of reduced haemoglobin is required. The blue colour of all these deoxygenated haemoglobins mixed with the red colour of oxygen haemoglobin. Therefore, a person with polycythaemia vera usually has a ruddy complexion with a bluish colour (cyanosis).

 

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