Describe the effects of low oxygen (O2) levels on both the systemic and pulmonary circulations.
Low oxygen levels cause lower oxygen saturation of haemoglobin and thereby less supply to body tissues. To compensate for this vasodilation occurs in systemic circulation so that more of blood reaches to tissue to meet oxygen demand.
In pulmonary circulation ,hypoxia (low oxygen levels) cause vasoconstriction to maintain the ventilation-perfusion ratio. In hypoxic alveoli where perfusion is low, capillary beds around this allveoli undergo vasoconstriction to lower the perfusion so that ventilation- perfusion ratio is not disturbed. This blood is shifted towards the more perfused alveoli. This hypoxia induced vasoconstriction is the major cause of pulmonary hypertension.
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