Define peripheral resistance. Explain several factors that cause it to increase

Peripheral resistance is the amount of friction encountered by blood as it flows through the blood vessels. Probably the most important factor that increases peripheral resistance is the narrowing of the diameter of a blood vessel (mainly by arterioles), which is called vasoconstriction. Vasoconstriction occurs normally due to an increase in sympathetic nervous system firing. It can also occur abnormally in atherosclerosis. Another factor that causes an increase in peripheral resistance is increased volume of blood in the vascular system or increased viscosity (thickness) of the blood. Regardless of the cause of this increase in peripheral resistance, the result is an increase in arterial blood pressure.