Local Regulation of Blood Flow Flashcards
(32 cards)
How do changes in metabolic demand affect local blood flow?
Vasodilator intermediates produced by local tissues reduce arteriole smooth muscle tone and induce vasodilation to metabolically active tissue. (called active hyperemia)
What metabolites promote vasodilation?
Potassium, adenosine, nitric oxide, prostaglandins, hydrogen peroxide
How can a tissue overcome arteriole occlusion?
Vasodilating metabolites can increase locally and force the arteriole to open enough to allow an occlusion to pass (reactive hyperemia)
What is autoregulation?
A tissue can increase peripheral resistance in response to an increase in blood pressure (or vice versa) so that there is no change to local blood flow
In what two types of tissue is autoregulation especially strong?
Coronary and cerebral
What are the metabolic mechanisms of autoregulation?
If arterial pressure increases, local blood flow will increase. This causes local vasodilating metabolites to be washed away. The decrease then permits an increase in smooth muscle tone and vasoconstriction results
What is the myogenic mechanism of autoregulation?
Increase in arterial pressure will cause an increase in the stretching of local smooth muscle. This opens mechanical calcium channels which trigger contractions that induce vasoconstriction
From what compound is nitric oxide produced?
L-arginine
What are two means of triggering an increase in nitric oxide production?
Chemical (serotonin, Ach) or mechanical (blood flow shear forces)
What are two functions of nitric oxide?
1) Serves as a tonic vasodilator which modulates resistance on a local level
2) Inhibits platelet activity
What are two main local vasodilators?
Nitric oxide and prostacyclin
What are three main local vasoconstrictors (and two platlet activators)?
Endothelin (no platelet activity though)
Serotonin
Thromboxane
What are the two main neurotransmitters that the sympathetic nervous system uses in its postganglonic fibers?
Norepinephrine
Neuropeptide Y
What is the receptor target of sympathetic system in the heart? in the vasculature?
1) beta-adrenergic receptors
2) alpha receptors
How is the magnitude and duration of sympathetic activation limited?
Postganglionic nerve fibers have a norepinephrine reuptake mechanism in their nerve terminals; norepinephrine’s presence will inhibit further release. The presence of vasodilator metabolites will also prevent release
What are the main effects of sympathetic innervation in the arterioles and venules?
In arterial system: promotes vasoconstriction (increases resistance)
in venous system: reduces compliance
In which tissues is sympathetic vasoconstrictive tone active?
Skin, inactive skeletal muscles, viscera, kidneys
In which tissues is sympathetic vasoconstrictive tone inactivated?
Brain, heart, and active skeletal muscle
What are the effects of the parasympathetic nervous system on blood flow?
Essentially none in the vasculature itself;
In the heart, lowers heart rate, atrial contractility, and A-V conduction
What is the effect of hormonal norepinephrine on blood flow?
increases heart rate and contractility (beta-adrenergic) increases vasoconstriction (alpha receptor)
What is the effect of hormonal epinephrine on blood flow?
increases heart rate and contractility (beta-adrenergic)
increases vasoconstriction (alpha receptor–high concentrations)
increases vasodilation in skeletal muscle (beta receptor)
What is the effect of hormonal renin on blood flow?
Responds to decreased arterial pressure to promote conversion of angiotensinogen to angiotensin I (which in turn becomes angiotensin II); angiotensin II promotes vasoconstriction
What is the effect of hormonal vasopressin on blood flow?
Released from the posterior pituitary in response to low pressure; promotes vasoconstriction and in the kidneys promotes sodium and water reabsorption (ADH)
What is the upstream pressure for blood delivery to the heart?
Since most coronary vessels are closed during ventricular contraction, aortic diastolic pressure is the driving force for blood flow
