37 - Vascular tone. Basal tone of blood vessels. Local, neural and humoral regulatory mechanisms

sections

vascular tone

extrinsic factors

intrinsic factors

intrinsic mechanism

vascular tone

• Vascular tone - degree of constriction experienced by a blood vessel relative to its maximally dilated state.

• All arterial and venous vessels under basal conditions exhibit some degree of smooth muscle contraction

• determines the diameter, and tone, of the vessel.

• Basal vascular tone differs among organs.

• The heart has - high vascular tone

• cerebral and renal circulations- low vascular tone.

• Vascular tone affects : pressure of blood and volume of blood that flows through the vessels

• affected by both intrinsic and extrinsic factors

extrinsic factors

extrinsic factors -orginate from outside the organ or tissue in which the blood vessel is located

• neurohumaral factors

• regulate arterial blood pressure by altering systemic vascular resistance

• involve activity of sympathetic nervous system as well as circulating

• angiotensin II - cause vasoconstriction leading to an increase in bp

• atrial natriuretic peptide thats decreases vascular tone

• regulated neural (autonomic) and humoral (circulating or hormonal) factors.

• The Neural factors include innervation by the parasympathetic and sympathetic nervous system.

intrinsic factors

intrinsic factors originate from the vessel itself or the surrounding tissue.

intrinsic mechanism

• are important for local blood flow regulation.

• sympathetic system involves adrenergic fibres that stimulates the heart and constricts blood vessels resulting in a rise in arterial pressure.

• The parasympathetic nervous system involves cholinergic fibres that secrete acetylcholine. It decreases cardiac activity and causes vasodilation

• The ANS has 5 effects on the heart:

  • Inotropic: strength of contraction

  • Bathmotropic: excitation of cardiomyocyte

  • Chronotropic: frequency of contraction

  • Dromotropic: conduction of impulses through cardiomyocytes

  • Tonotropic: tone of cardiomyocyte

  • Sympathetic effect: All the above five effects increase ●

  • Parasympathetic effect: All the above five effects decrease