Venous constriction results in an increased venous return to the heart. This increases CO by increasing SV, and so allows the HR to partially reduce towards normal. These combined effects rapidly return blood pressure towards normal. However, the blood volume requires a longer time to be restored. Long-term effects Decreased capillary pressure promotes fluid reabsorption from tissues.
Fluid ingestion replaces fluids 'borrowed' from tissues.
Sympathetic control is particularly strong in skin, skeletal muscle, gut and kidneys, but weak in heart and brain. Hence blood flow to kidneys is reduced, further helping to retain water. Increased erythropoietin levels stimulate production of red blood cells by bone marrow. These processes may take several days to return blood volume to normal. There are no long term ill effects.