Vascular smooth muscle
Vascular smooth muscle refers to the particular type of
smooth musclefound within, and composing the majority of the wall of blood vessels.
Vascular smooth muscle contracts or relaxes to both change the volume of blood vessels and the local
blood pressure, a mechanism that is responsible to redistribution of the blood within the body to areas where it is needed (i.e. areas with temporarily enhanced oxygen consumption). Thus the main function of vascular smooth muscle tonusis to regulate the caliber of the blood vessels in the body. Excessive vasoconstrictionleads to hypertension, while excessive vasodilationas in shock leads to hypotension.
Arteries have a great deal more
smooth musclewithin their walls than veins, thus their greater wall thickness. This is because they have to carry pumped blood away from the heart to all the organs and tissues that need the oxygenated blood. The endothelial lining of each is similar.
Vascular smooth muscle is innervated primarily by the
sympathetic nervous systemthrough adrenergic receptors ( adrenoceptors). Three types of adrenoceptors are present within vascular smooth muscle cells: , and . The main endogenous agonist of these cell receptors is norepinephrine(NE).
adrenergic receptors exert opposite physiologic effects in the vascular smooth muscle under activation:
* "receptors". Under NE binding receptors cause
vasoconstrictioni.e. contraction of the vascular smooth muscle cells decreasing the diameter of the vessels. receptors are activated in response to shock or hypotension as a defensive reaction trying to restore the normal blood pressure. Antagonists of receptors ( doxazosin, prazosin) cause vasodilationi.e. decrease in vascular smooth muscle tone with increase of vessel diameter and decrease of the blood pressure. (See also receptor antagonist)
Agonists of receptors in the vascular smooth muscle lead to vasoconstriction. However in clinical practice applied intravenously drugs being agonists of receptors ( chlophazolin) leads to powerful vasodilation and decrease in the blood pressure by presynaptic activation of receptors in the sympathetic ganglia. This presynaptic effect is predominant and completely overrides the vasoconstrictive effect of the receptors in the vascular smooth muscle.
* "receptors". Agonism at receptors causes
vasodilationand hypotension, i.e. the effect is opposite of the one resulting from activation of and receptors in the vascular smooth muscle cells. Usage of agonists of receptors as hypotensive agents is less widespread due to adverse effects such as unnecessary bronchodilation in lungs and increase in blood sugarlevels.
* [http://www.ii.bham.ac.uk/clinicalimmunology/CISimagelibrary/smoothmuscle.htm Image of smooth muscle in the arterial walls]
* [http://www.antibodypatterns.com/smoothmuscle.php Smooth muscle in stomach wall]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Smooth muscle tissue — Smooth muscle … Wikipedia
Smooth muscle — is a type of non striated muscle, found within the tunica media layer of large and small arteries and veins, the bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the… … Wikipedia
Muscle fascicle — Structure of a skeletal muscle. (Fascicle labeled at bottom right.) Latin fasiculus muscularis Gray s … Wikipedia
Muscle spindle — Latin fusus neuromuscularis Code TH H3.11.06.0.00018 Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via … Wikipedia
muscle — muscleless, adj. muscly, adj. /mus euhl/, n., v., muscled, muscling, adj. n. 1. a tissue composed of cells or fibers, the contraction of which produces movement in the body. 2. an organ, composed of muscle tissue, that contracts to produce a… … Universalium
Muscle — For other uses of Muscle , see Muscle (disambiguation). A top down view of skeletal muscle Muscle (from Latin … Wikipedia
Muscle contraction — See also: Twitch and Tremor Top down view of skeletal muscle Muscle fiber generates tension through the action of actin and myosin cross bridge cycling. While under tension, the muscle may lengthen, shorten, or … Wikipedia
Skeletal striated muscle — A top down view of skeletal muscle Latin textus muscularis striatus skeletalis Code TH … Wikipedia
Cardiac muscle — Dog Cardiac Muscl … Wikipedia
Connective tissue in skeletal muscle — Each skeletal muscle consists of two kinds of tissue: connective tissue, and muscle tissue. Connective tissue of skeletal muscle contains: Layers of connective tissue Tendon, and sometimes aponeurosis The layers of connective tissue have a major… … Wikipedia