Sympathetic NS Flashcards
what neurones and receptors are involved in the sympathetic NS?
Ach on nicotinic receptors and NA on alpha/beta receptors
how is adrenaline release stimulated?
a cell body releases Ach on nicotinic receptor in adrenal tissue which then causes stimulation of adrenaline release
what are the two sources of outflow?
thoracic and lumbar
what is Thoracic outflow?
the spine in the upper back and lower abdomen
what is lumbar outflow?
the spine in the lower back
where are the ganglia that are involved in sympathetic NS?
close to the spinal cord
what is the pathway that results in NA onto alpha/beta receptors?
tyrosine - dopa - dopamine - NA in storage vesile - NA release
where do the neurones that release NA exist in the body?
in the brain as well as the sympathetic NS
what did dale provide evidence for?
that two distinct classes of adrenoreceptor exist
how did dale discover this?
observed that a vasoconstrictor effect of adrenaline becomes a vasodilator effect when pre-treated with ergot
what effect did ergot have in this observation?
in the absence of ergot, there was a large alpha mediated constriction yet when ergot blocked alpha, there was a large beta mediated dilation
what did ahlquist do?
observed responses to adrenaline, NA and isoprenaline in smooth muscle
what are alpha receptors sensitive to?
highly sensitive to adrenaline and noradrenaline
what are alpha receptors not sensitive to?
isoprenaline
what are beta receptors sensitive to?
highly sensitive to isoprenaline
what are beta receptors less sensitive to?
more sensitive to adrenaline than noradrenaline
what did lands do?
identified two types of beta receptor
what does beta 1 receptor cause?
increases in rate and force of cardiac contraction
what do beta 2 receptors do?
mediate bronchodilation and vasodilation
what do alpha 1 receptors do?
vasoconstriction and contraction
what do alpha 2 receptors do?
inhibition of NA release
what do direct drugs do?
mimic or block the effect of NA/A by acting on beta or alpha receptors
what do indirectly acting drugs do?
increase or decrease NA availability by non-receptor mechanisms
what are examples of ways in which an increase or decrease in NA is caused?
block of neuronal uptake or inhibition of MAO
what do directly acting alpha 1 agonists do?
mimic the effect of NA/A causing vasoconstriction in vascular smooth muscle
what is an example of a directly acting alpha 1 agonist?
phenylephrine
what are the clinical uses of alpha 1 agonists?
they cause vasoconstriction so nasal decongestion and raising low blood pressure
what effect do alpha 1 antagonists have?
inhibit vasoconstriction so reduces blood pressure
what is an example of an alpha 1 antagonist?
prazosin
what are the clinical uses for alpha 1 antagonists?
relaxing prostatic smooth muscle to allow urine flow
how is NA able to limit its own release?
as stimulation of alpha 2 adrenoceptors inhibits NA release
what does a reduction in NA release cause?
reduction in vasoconstriction and lower BP
what does NA cause?
contraction of smooth muscle
what is an example of an alpha 2 agonist?
clonidine
what do alpha 2 agonists do?
stimulate alpha 2 agonists which prevent NA release
what do alpha 2 antagonists do?
block the inhibition of NA release by blocking the alpha 2 receptor
what effect do alpha 2 antagonists have?
increase the amount of NA available to stimulate the postsynaptic receptors
what is an example of an alpha 2 antagonist?
yohimibine idazoxane
what type of drug is not used clinically?
alpha 2 antagonists
what does beta adrenoceptor stimulation cause?
causes heart rate and force of contraction to increase and more renin released from the kidney which also causes an increased BP
what are the clinical uses of beta agonists and antagonists?
cardiac arrest and low BP
what is dobutamine?
beta 1 agonist
what are beta 1 antagonists used to treat?
hypertension and angina
what are the non-selective beta drugs?
propanolol and timolol
what are the beta 1 selective drugs?
atenolol
what do beta 2 agonists do?
cause stimulation of beta 2 receptors causing bronchodilation and vasodilation
what are beta 2 agonists used to treat?
asthma
what are some examples of beta 2 agonists?
salbutamol, fenoterol and salmeterol
what are the adverse effects of beta 2 agonists?
tachycardia and fine muscle tremor if beta 2 stimulation
are there any beta 2 antagonist clinical uses?
no, however used for pharmacological research
what does MAO do?
converts NA that has been uptakes from the synaptic cleft into deaminated metabolites
what do MAO inhibitors do?
increase the synaptic availability of NA by blocking its breakdown
what is phenelzine?
an MAO blocker
what effect does cocaine have?
it blocks the neuronal uptake of NA increasing its synaptic concentration
what does cocaine block?
the dopamine transporter in dopaminergic neurones
what effect does amphetamine have?
displaces the NA from its storage vesicles and displaces the direction of the uptake pump, increasing its concentration in the cleft
what physiological effects of cocaine and amphetamine?
rapid heart rate, elevated blood pressure and decreased GI motility
