Blood pressure in the arterial system is controlled by changes in the cardiac rate, total peripheral resistance and blood volume. And they are arranged by centers within the medulla oblongata.
Reasons Affecting Blood Pressure
As these vessels have the tiniest diameters, resistance to flow in the arterial system is greatest in the arterioles. As a result, blood flow rate and stress are decreased in the capillaries. Capillaries are located downstream of the high resistance imposed by the arterioles. What is more, within the capillaries, the blood flow and stress rate are farther decreased . Their cross-sectional area is more greater by this truth as a whole, thanks to their bigger number, than the cross-sectional area of arteries and arterioles.
Because of vasodilation and vasoconstriction, variations in the diameter of arterioles simultaneously affect on two sides. On one hand, they have an influence on the arterial blood pressure ” upstream” from the capillaries. On the other hand, they have an influence on blood flow across capillaries. The total peripheral resistance and the cardiac rate, stroke volume (decided basically by the blood volume) are the most significant variables affecting blood stress. An improvement in any of those, once do not offset by a reduction in another variable will lead to an increased blood pressure.
As a result, blood pressure can be controlled by the kidneys, and by the sympathoadrenal system. In addition, the kidneys have function of regulating blood volume. Increased activity of the sympathoadrenal system can improve blood pressure, according these two ways as following:
- by promoting an increased cardiac output
- by stimulating vasoconstriction of arterioles (improving total peripheral resistance)