S5: ANS, control of blood pressure & hypertension

Question 1

Detail the neurotransmitters and receptors involved in the autonomic nervous system

Answer 1

Two divisions of the ANS: parasympathetic (acetylcholine) & sympathetic (acetylcholine and noradrenaline)
Adrenoreceptors, muscarinic ACh receptors, nicotinic ACh receptors

Question 2

Name the different inputs by the autonomic nervous system and their effects on the heart

Answer 2

Parasympathetic input to the heart -> acts on M2 receptors -> decreases heart rate & decreases AV node conduction velocity
Sympathetic input to heart -> mainly on B1 receptors -> increases heart rate & increases force of contraction

Question 3

Describe the effect of sympathetic input on pacemaker potentials

Answer 3

Increases pacemaker potential slope
Mediated by B1 receptors (GPCRs)
Increase cAMP -> speeding up pacemaker potential

Question 4

Describe the effect of parasympathetic input on pacemaker potentials

Answer 4

Decreases pacemaker potential slope
Mediated by M2 receptors (GPCRs)
Increased K+ conductance & decrease cAMP

Question 5

How does noradrenaline increase force of contraction?

Answer 5

Increase in cAMP -> activates PKA
Phosphorylation of Ca2+ channels increase Ca2+ entry during the plateau of the AP
Increased uptake of Ca2+ in SR (more Ca2+ available for release)

Question 6

Describe the mechanisms which control contraction of vascular smooth muscle cells

Answer 6

Most arteries and veins have A1 adrenoreceptors (coronary & skeletal muscle vasculature also have B2 receptors)
Activating B2 adrenoreceptors causes vasodilation
Activating A1 adrenoreceptors causes vasoconstriction
Local increases in metabolites also have a strong vasodilator effect (active tissue produces more metabolites)

Question 7

Explain the role of the autonomic nervous system in controlling peripheral resistance (binding of adrenaline)

Answer 7

Physiological concentration circulating adrenaline will preferentially bind to B2 adrenoreceptors
At higher concentrations adrenaline will also activate A1 receptors

Question 8

Explain how blood pressure is controlled in the short and longer term

Answer 8

Short term: baroreceptor reflex

Longer term: renin-angiotensin-aldosterone system, sympathetic nervous system, ADH, ANP

Question 9

Describe the baroreceptor reflex

Answer 9

Nerve endings in the carotid sinus and aortic arch are sensitive to stretch
Increases arterial pressure stretches these receptors, decreased pressure stretches less
Works well to control acute changes in BP
Does not control sustained increases because the threshold for baroreceptor firing resets

Question 10

Describe the role of the renin-angiotensin-aldosterone system in maintain blood pressure

Answer 10

Decreasing circulating volume stimulates renin release
Angiotensin II causes vasoconstriction, stimulates Na+ reabsorption at kidney, stimulates aldosterone (all to increase BP)
Aldosterone: acts on principal cells of collecting ducts, stimulates Na+ and therefore water reabsorption

Question 11

How does ADH act to maintain BP?

Answer 11

Only released in a response to a relatively large fall in blood volume
Its more sensitive to changes in plasma osmolarity (retains water by increasing reabsorption)

Question 12

How does ANP act to maintain BP?

Answer 12

Released in response to an increase in circulating blood volume
Acts on the kidneys to promote the loss of sodium and hence reduces blood volume

Question 13

Define the stages of hypertension

Answer 13

Stage 1 = > 140/90 mmHg
Stage 2 = > 160/100 mmHg
Severe hypertension = > 180 systolic or > 110 diastolic

Question 14

List impacts of hypertension on organs and tissues in the body

Answer 14

Increased CVS disease risk
Stroke
Vision loss
Kidney disease/failure
Sexual dysfunction