The peripheral circulatory system adapts to changes in the body such as:

• Assumption of an upright posture—Circulation is maintained by immediate changes in heart rate and then by adjustment in arterial resistance (the amount of constriction of the arterial vessels).

• Hemorrhage—Severe blood loss is compensated for by vasoconstriction (increase in heart rate and constriction of arterioles) and capillary fluid resorption (re-absorption of fluid).

• Muscle Activity—As cardiac output increases, arterial blood pressure increases, and veins and arteries to contracting muscles dilate, providing more blood to the muscle and also removing the excess heat generated by working muscle.

• Temperature and other changes—When we are chilled and our temperature decreases, veins (as well as arteries) become constricted (vasoconstriction) and skin blood flow decreases. When we are overheated or have a fever, skin blood flow increases over 10 times the norm. Other conditions can cause vasoconstriction such as hyperventilation (overly rapid and deep breathing), cold showers, and extreme stress or strong emotions.

Mainly, compensations are reflexive changes in resistance vessels with adjustments in tone in veins.