Question

Describe extrinsic controls regulating the diameter of smooth muscle in skeletal muscle arterioles.

Answer 1

• Resistance to blood flow through a vascular network is determined by the size of individual vessels( length and diameter) , physical characteristics of blood etc..
• Of many factors , change in vessel diameter is most important quantitatively for regulating blood flow within an organ as well as for regulating arterial pressure.
• Change in vessel diameter , particularly in small arteries and arterioles , will enable organ to adjust their blood accroding metabolic demand of tissue.
• If an organ need to adjust blood flow , cell surrounding blood vessel release vasoactive substances , which can constrict or dialate the resistance vessels.
• Other than local regulatory mechanisms, there are extrinsic mechanisms acting on the vasculature to regulate vessel diameter.
• One important extrinsic mechanism regulating vascular diameter operates through the autonomic innervation of blood vessels. In general, sympathetic adrenergic influences acting through vascular alpha-adrenoceptors cause resistance vessels as well as veins to be partially constricted under basal conditions. This is termed "sympathetic vascular tone." Therefore, removal of sympathetic adrenergic influences (for example, by administration of an alpha-adrenoceptor antagonist or by sympathectomy) leads to vasodilation and an increase in organ blood flow.
• A second type of extrinsic influence on the vasculature is circulating vasoactive hormones such as angiotensin II, epinephrine and norepinephrine, vasopressin (antidiuretic hormone, ADH), atrial natriuretic peptide (ANP), and endothelin.
• Hence both neural and hormonal factors primarily function in regulation of arterial pressure by changing systemic vascular resistance.