heart and blood vessel disorders
Low Blood Pressure
Changing the diameter of arterioles and veins
Muscle tissue (called smooth muscle) within the walls of arterioles allow these blood vessels to widen (dilate) or narrow (constrict). The more constricted arterioles are, the greater their resistance to blood flow and the higher the blood pressure. Constriction of arterioles increases blood pressure because more pressure is needed to force blood through the narrower space. Conversely, dilation of arterioles reduces resistance to blood flow, thus reducing blood pressure. The degree to which arterioles are constricted or dilated is affected by Nerves that contract smooth muscle in the arterioles, thus reducing their diameter Endocrine Function that are primarily made by the kidneys Certain drugs Veins also play a role in the control of blood pressure, although their effect on blood pressure is much less than that of arterioles. Veins dilate and constrict to change how much blood they can hold (capacity). When veins constrict, their capacity to hold blood is reduced, allowing more blood to return to the heart from which it is pumped into the arteries. As a result, blood pressure increases. Conversely, when veins dilate, their capacity to hold blood is increased, allowing less blood to return to the heart. As a result, blood pressure decreases. 