Session 5- Autonomic nervous system/ Control of Blood pressure and Hypertension Flashcards
what happens when the heart is denervated
it still beats but at a faster rate
which parasympathetic nerve innervates the heart
the 10th cranial vagus nerve
where does where do the parasympathetic nerves in the heart synapse
synapse with postganglionic cells on epicardial surface or within walls of heart predominantly at SA and AV node
where do sympathetic nerves innervate the heart
innervate SA AV node and myocardium
what receptors do the parasympathetic nerves act on
M2 receptors
what receptors do the sympathetic receptors act on
b1
what does sympathetic activity do to the heart
sympathetic effect mediated by b1 receptors
G-protein coupled receptors
increased cAMP
speeds up pacemaker potential
increases slope
what does parasympathetic activity do to the heart
parasympathetic effect mediated by M2 receptors
G-protein coupled receptors
increase K+ conductance and decrease cAMP
opening of HCN channels
how does NA increase force of contraction
NA acting on b1 receptors in myocardium causes an increase in cAMP -> activates pKa
1) phosphorylation of Ca2+ channels entry during the plateau of the AP
2) Increased uptake of Ca2+ in sarcoplasmic reticulum
- more Ca2+ available for release from stores
Leads to increase force of contraction
what receptors do most arteries and veins have
a1 adrenoceptors
what receptors to coronary and skeletal muscles have as well as a1
b2
what innervation do most vessels have
sympathetic except some which also have parasympathetic- erectile tissue
what does having a basal vasomotor level of tone allow
both dilatation and constriction can occur
what does increased sympathetic output cause
vasoconstriction
more activation of alpha 1
more NA released
what does decreased sympathetic input cause
vasodilation
less activated of alpha 1
less NA released
which blood vessels have b2 adrenoceptors as well as a1
skeletal muscle
myocardium
liver
what effect does circulating adrenaline have on blood vessels
it has a higher affinity for b2 adrenoceptors than a1 receptors
at physiological concentration circulating adrenaline will preferentially bind to b2 adrenoceptors
at higher concentrations adrenaline will also activate a1 receptors
what receptors cause vasodilation
b2 adrenoceptors
G alpha s activates adenylyl cyclase which increases cAMP ->pKa -> opens potassium channeks + inhibits MLCK ->relaxation of smooth muscle
what receptors cause vasoconstriction
a1 adrenoceptors
g alpha q
stimulates IP3 production
increase in [Ca2+]in from stores and via influx of extracellular Ca2+ -> contraction of smooth muscle
DAG activates PKC which inhibits MLCP
what role do metabolites play
active tissue produce more metabolites
local increases in metabolites have a stronger vasodilator effect
metabolites are more important for ensuring adequate perfusion of skeletal and coronary muscle than activating b2 receptors
what is the baroreceptor reflex
inhibition of SNS to heart and vessels
Activation of PNS to heart in response to increase arterial pressure
what are sympathomimetics
mimic action of the sympathetic nervous system - agonists
- a adrenoceptor agonist - adrenaline in anaphylactic shock
- b1 adrenoceptor- dobutamine given in cardiogenic shock
-b2 adrenoceptor agonists salbutamol
what are cholinergics
muscarinic agonists
- pilocarpine
- used in treatment of glaucoma
antagonists
- atropine or tropicamide
- increases heart rate, bronchial dilation
- used to dilate pupils for examination of the eye
alpha adrenoceptor antagonists
a1 antagonists- prazosin
anti hypertensive agent- inhibits NA action on vascular smooth muscle
-inhibits NA action on vasculature smooth muscle a1 receptors- vasodilation
