Factors influencing production and maintenance of blood pressure
Heart beat
During systole, the arterial pressure increases. The rate at which blood enters the arterial system exceeds the rate at which it drains through arterioles and capillaries, increasing the pressure.
During diastole, the BP decreases since blood passes out of arteries into capillaries. When other three factors remain constant, an increase in rate of the heart raises BP and decrease in heart rate will cause a fall in BP.
Peripheral resistance
Peripheral resistance is caused by internal friction produced by the viscosity of blood and mostly present in arterioles and capillaries (peripheral circulation). BP is directly proportional to peripheral resistance. When most capillaries are opened peripheral resistance decrease causes reduction in BP.
BP = TPR x Cardiac output
Resistance varies inversely with the fourth power of the radius of the vessels and directly proportional to the viscosity, and length of the vessel. Total peripheral resistance (TPR) is the resistance to flow of blood in the whole of systemic vessels.
Elasticity of arteries
The elastic recoil of large arteries is responsible for the continuous flow of blood in the arterioles and capillaries. During systole when more blood enters aorta and large arteries, they expand to store the blood i.e. potential energy is stored and during diastole, the stored blood is released due to elastic recoil of the walls of arteries causing blood to flow into arterioles during diastole.
Arterial stiffening increases systolic pressure (due to reduced expansion of artery) and decreases diastolic pressure (since less blood is stored by reduced expansion).
Volume flow
An increase and decrease in the blood volume through the circulatory system causes either increase or decrease in BP. When hemorrhage occurs in a large artery, the BP falls immediately due to drop in the blood volume. On moderate hemorrhage and when small arteries are cut, the fall in BP will be negligible because of the compensatory vasomotor mechanism and spleenic constriction.