What changes occur in the circulatory system when a person stands up from a prone position?

Question

How do these changes affect the heart rate and blood pressure of the individual?

Answer 1

Typically when we stand from prone, the blood in our venous system tends to pool in our lower extremities. This causes a reduction to the blood flow to our heart, in medical terms, decreased preload. Since there is a small decrease to the total volume of blood going to the heart, the heart compensates by increasing its heart rate. People may experience a very small drop in blood pressure only for a short time.
In healthy individuals, the little changes in heart rate and blood pressure are not enough for us to feel any different.

Answer 2

There are compensatory mechanisms that prevent too severe drop in blood pressure. The carotid sinus has pressure receptors that determine if there's a significant change in MAP (mean arterial pressure) and respond by increasing or decreasing the capacitance of the vessels thereby compensating. In the elderly, these mechanisms are sluggish and decreased.