Question

Describe the physiologic changes that affect blood pressure and other aspects of cardiovascular function as the patient goes from the supine to standing position; explain the impact of alpha- and beta-adrenergic blockers on those compensatory processes.

Answer 1

Gravitational forces affect not only material objects but also the human body.When the person lies down gravitational forces are similar on the thorax ,abdomen and legs as these compartments lie in the horizontal plane..Thereby the venous blood pressure and volume are distributed evenly throughout the body.But when he stands up ,due to the gravitys influence the vascular volume causing blood to accumulate in the lower extremities.Because venous compliance is high and the veins expand with blood,most of the bloodshift occurs in the veins.Therefore venous volume and pressure become very high in the feet and lower limbs while standing.This shift in blood volume decrease thoracic venous blood volume and therefore CVP decreases.This decreases right ventricular filling pressure ,leading to a decline in stroke volume by the Frank-Starling mechanism.

2 There are two types of adrenergic receptors alpha and beta.Beta blockers produce bronchoconstriction,vasoconstriction of some arterioles,miosis and decreased contractility of skeletal muscle.it increases the hert rate and force of contraction,increases renin secretion which increases blood pressure.Alpha increases the force of contraction,vasoconstriction increases BP,mydriasis.When alphal receptors in vascular tissues of muscles are stimulated the arterioles and venules constrict which increaseses peripheral resistance and blood return to the heart.Circulation is improved and BP increases.