Session 5- Autonomic nervous system/ Control of Blood pressure and Hypertension

Question 1

what happens when the heart is denervated

Answer 1

it still beats but at a faster rate

Question 2

which parasympathetic nerve innervates the heart

Answer 2

the 10th cranial vagus nerve

Question 3

where does where do the parasympathetic nerves in the heart synapse

Answer 3

synapse with postganglionic cells on epicardial surface or within walls of heart predominantly at SA and AV node

Question 4

where do sympathetic nerves innervate the heart

Answer 4

innervate SA AV node and myocardium

Question 5

what receptors do the parasympathetic nerves act on

Answer 5

M2 receptors

Question 6

what receptors do the sympathetic receptors act on

Answer 6

b1

Question 7

what does sympathetic activity do to the heart

Answer 7

sympathetic effect mediated by b1 receptors
G-protein coupled receptors
increased cAMP
speeds up pacemaker potential

increases slope

Question 8

what does parasympathetic activity do to the heart

Answer 8

parasympathetic effect mediated by M2 receptors
G-protein coupled receptors
increase K+ conductance and decrease cAMP
opening of HCN channels

Question 9

how does NA increase force of contraction

Answer 9

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

Question 10

what receptors do most arteries and veins have

Answer 10

a1 adrenoceptors

Question 11

what receptors to coronary and skeletal muscles have as well as a1

Answer 11

b2

Question 12

what innervation do most vessels have

Answer 12

sympathetic except some which also have parasympathetic- erectile tissue

Question 13

what does having a basal vasomotor level of tone allow

Answer 13

both dilatation and constriction can occur

Question 14

what does increased sympathetic output cause

Answer 14

vasoconstriction
more activation of alpha 1
more NA released

Question 15

what does decreased sympathetic input cause

Answer 15

vasodilation
less activated of alpha 1
less NA released

Question 16

which blood vessels have b2 adrenoceptors as well as a1

Answer 16

skeletal muscle
myocardium
liver

Question 17

what effect does circulating adrenaline have on blood vessels

Answer 17

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

Question 18

what receptors cause vasodilation

Answer 18

b2 adrenoceptors
G alpha s activates adenylyl cyclase which increases cAMP ->pKa -> opens potassium channeks + inhibits MLCK ->relaxation of smooth muscle

Question 19

what receptors cause vasoconstriction

Answer 19

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

Question 20

what role do metabolites play

Answer 20

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

Question 21

what is the baroreceptor reflex

Answer 21

inhibition of SNS to heart and vessels

Activation of PNS to heart in response to increase arterial pressure

Question 22

what are sympathomimetics

Answer 22

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

Question 23

what are cholinergics

Answer 23

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

Question 24

alpha adrenoceptor antagonists

Answer 24

a1 antagonists- prazosin

anti hypertensive agent- inhibits NA action on vascular smooth muscle
-inhibits NA action on vasculature smooth muscle a1 receptors- vasodilation

Question 25

beta adrenoceptor antagonists

Answer 25

propanolol

• non selective b1/b2 antagonist
• slows heart rate and reduces force of contraction (b1) but also acts on bronchial smooth muscle (b2) bronchoconstriction

atenolol
-selective b1 (cardio-selective) - less risk of bronchoconstriction

Question 26

what is the normal range for diastolic blood pressure

Answer 26

60-80 mmHg

Question 27

what is the normal range for systolic blood pressure

Answer 27

90-120 mmHg

Question 28

Explain how the baroreceptor reflex prevents acute

fluctuations in arterial BP

Answer 28

A reduction in BP would cause less firing of baroreceptors
which would be detected by cardiovascular control centre in
the medulla leading to reduced vagal drive and increased
sympathetic drive to heart to increase cardiac output.
Importantly it will also increase sympathetic drive to
peripheral resistance vessels to cause vasoconstriction.
An increased BP would reduce sympathetic drive to the heart
and peripheral vessels and increase vagal drive to the heart.
This will reduce cardiac output and reduce peripheral
vasoconstriction.

Question 29

stage 1 hypertension

Answer 29

Stage 1 hypertension Clinic blood pressure is 140 /9 0

mmHg or higher

Question 30

stage 2 hypertension

Answer 30

Stage 2 hypertension Clinic blood pressure is 160 /100

mmHg or higher

Question 31

severe hypertension

Answer 31

Severe hypertension Clinic systolic blood pressure is 180
mmHg or higher or clinic diastolic blood pressure is 110
mmHg or higher.