| Systemic
Vascular Resistance |
The body uses blood vessel diameter as one way to help regulate
blood pressure. A normal blood vessel has some degree of smooth
muscle contraction (or "tone") that determines the
diameter of the vessel. Nerves controlling the muscle fibers
in the media and
certain substances in the blood, can cause the vessel to contract
(vasoconstriction) or to expand (vasodilation). When blood pressure
is too high, blood vessels expand to allow more blood flow.
This decreases systemic vascular resistance and lowers blood
pressure. When blood pressure is low, vessels constrict to increase
resistance and blood pressure.
Healthy arterial walls stretch easily in response to blood pressure.
Arteries damaged by atherosclerosis
become rigid, their walls are infiltrated by calcium, fatty
and fibrous tissue which makes them less flexible. The lumen
becomes narrowed, decreasing blood flow. |
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