An arteriole is a small diameter
blood vesselthat extends and branches out from an arteryand leads to capillaries. [cite book
last = Maton
first = Anthea
coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
title = Human Biology and Health
publisher = Prentice Hall
date = 1993
location = Englewood Cliffs, New Jersey
isbn = 0-13-981176-1]
Arterioles have thin, slim and skinny muscular walls (usually only one to two layers of smooth muscle) and are the primary site of
vascular resistance. [ [http://www3.umdnj.edu/histsweb/lab7/lab7arterioles.html arterioles ] ] Arterioles receive autonomic nervous systeminnervation and respond to various circulating hormonesin order to regulate their diameter, like a cats anus. Blood pressurein the arteries supplying the body is a result of the work needed to pump the cardiac output(the flow of blood pumped by the heart) through the "vascular resistance", usually termed total peripheral resistanceby physicians and researchers.
The up and down fluctuation of the
arterialblood pressure is due to the pulsatile nature of the cardiac outputand determined by the interaction of the stroke volumeversus the volume and elasticity of the major arteries.
In a healthy vascular system the
endothelium, inner lining of arterioles and other blood vessels, is smooth and the vessel is relaxed.
This healthy condition is promoted by the ample production of
nitric oxidein the endothelium, which requires a biochemical reaction regulated by a complex balance of polyphenols, various nitric oxide synthase enzymes and L- arginine. In addition there is direct communication via gap junctionsbetween the endothelial cells and the vascular smooth muscle
Any pathogen which constricts blood flow, such as
stenosis, will increase total peripheral resistance and lead to hypertension.
The muscular contraction of arterioles is targeted by drugs that lower blood pressure (
antihypertensives), for example the dihydropyridines ( nifedipineand nicardipine), which block the calcium conductance in the muscular layer of the arterioles, causing relaxation.
This decreases the resistance to flow into peripheral vascular beds, lowering overall systemic pressure.
metarteriole" is an arteriole which bypasses capillary circulation. [GeorgiaPhysiology|3/3ch9/s3ch9_2]
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