Lecture 13 – Reflex control of the CVS

Question 1

Cardiovascular reflexes

Answer 1

Cvs responses to change through sensory ad afferent pathways.

Question 2

Stimulation of sensory receptors (4)

Answer 2

Arterial baroreceptors
Cardiac receptors
Arterial chemoreceptors
Muscle metaboreceptors

Question 3

Central pathways (3)

Answer 3

Medulla relay station (NTS) area in BS.

Vagal motor neurone (nucleus ambiguous) area in BS and integrates the activity of the vagus nerve.

Pre-sympathetic neurones (RVLM) - located in BS/medulla.

Question 4

Effects of BP via S and vagus nerved (3)

Answer 4

Heart - HR/ Contractility
Arterioles - Resistance vessels/TPR.
Veins - CVP - capacitance vessels can be constricted, increases CVP/CO (starlings law).

Question 5

Excitatory inputs (3)

Answer 5

Arterial chemoreceptors detect low CO2 or include H+ muscle metaboreceptors (work).
Stimulation of reflexes increases CO,TPR and BP.
PRESSOR response

Question 6

Inhibitory inputs (3)

Answer 6

Arterial baroreceptors and cardiac receptors
Stimulation of reflexes decrease CO, TPR, BP.
DEPRESSOR response.

Question 7

Arterial baroreceptors (5)

Answer 7

Vital to maintain blood flow to brain/myocardium.
There are NO BF SENSORS, monitors BP in CAROTID and CORONARY arteries. Monitoring BP tells us about BF due to CO x TPR = Pa.
A decrease in Pa = decrease in CO, TPR so compromised BF.

Carotid arteries pressure detected by baroreceptors on carotid sinus and the aorta, when stretched signal along carotid sinus nerve and the vagus/glossopharyngeal nerve to the base of the brain.

Question 8

Baroreceptors respond to changes in pressure (4)

Answer 8

Not much firing at rest, as P IN fast firing which eventually slows down and becomes constant, but at a higher level than before. ADAPTATION to a new normal level.
For a DE in P firing slows down proportionately.

When there is a long term high/low pressure the threshold can change e.g. hypertension patients have a new normal so there baroreceptors are less activated.
During exercise, P IN so firing of BR and BP IN. These slow down once a new steady state of BP is reached and adapt to a new normal.

Question 9

Effect of IN BP on baroreflex (1,4)

Answer 9

FC

Question 10

Effect of DE BP on baroreflex ()

Answer 10

FC

Question 11

Cardiac receptors (4)

Answer 11

Venoatrial mechanoreceptors - detects increased cardiac filling pressure, increase sympathetic activity, tachycardia in order to get more blood back to the heart.
Bainbridge effect/reflex - increased diuresis (increased production of urine via increased ADH, AMP and RAAS system). S activity to kidneys switched off and IN in GFR, reduces BV.

Stimulated by over distension of the ventricles. VD to reduce BP as protective preload.

Nociceptive sympathetic afferents - stimulated by K/H/bradykin during ischaemia. Mediate the pain of angina and MI, fibres converge onto the same neurone in spianl cord as somatic afferents. There will be a reflex increased sympathetic activity - pale sweaty, tachycardia or angina/MI systems.

Question 12

Arterial chemoreceptors (5)

Answer 12

Located in the carotid and aortic bodies.
Stimulated by low O2 (hypoxia) and high CO2 (hypercapnia).
Well supplied within blood flow 20 ml/g/min.
Regulate ventilation and drive cardiac reflexes during asphyxia,shock (systemic hypotension) and haemorrhage.
When BP is below the range of baroreflex (max unloaded) the chemoreceptors are still active and may compensate.

Question 13

Arterial chemoreceptors - PRESSOR response (4)

Answer 13

When BP falls, the min level of baroreflex (max unloaded), chemoreceptors detect this and try to raise BP, resulting in:

• increased S activity
• tachycardia increased selective arterial/venous constriction
• increased CO and BP - especially preservation of cerebral BF.

Question 14

Muscle metaboreceptors (work receptors) (3)

Answer 14

• Sensory fibres in Group IV motor fibres located in skeletal muscle
• Pressor response
Important duing isometric exercise.
o Continually contracted muscle but joint angle

Question 15

Muscle metaboreceptors (work receptors) - in detail (1,3,3)

Answer 15

• Sensory fibres in Group IV motor fibres located in skeletal muscle
o Activated via metabolites K+, lactate, adenosine.
• Pressor response
o Increased sympathetic activity
o Tachycardia increase arterial/venous constriction.
o Increase cardiac output/blood pressure.
• Important during isometric exercise
o Continually contracted muscle but joint angle and muscle length do not change e.g. weight lifting/handgrip.
o Higher BP drives blood into the contracted muscle to maintain perfusion.
o These muscles undergo metabolic hyperaemia allowing blood flow to the contracted tissue.

Question 16

Human muscle metaboreceptors in static exercise (3)

Answer 16

Human muscle metaboreceptors in static exercise:
• Maintaining hand grip exercise.
• Metaboreceptor afferent fibres blocked by local anaesthetic fibres (LA) injected into muscle prevent pressor response.
• Increasing arterial BP drives blood into contracted muscle. Bring in O2 and glucose, take away CO2.

Question 17

Central role of the nucleus tractus solitarius /LINKS ON FC

Answer 17

FC

Question 18

Experimental link between CVLM and RVLM (6)

Answer 18

Experimental link between CVLM and RVLM-1:

1) Intravenous injection - phenylephrine (alpha1 agonist increases TPR and BP).
2) BP rises and loads baroreceptors on the carotid arteries and the aorta will become ‘loaded’.
3) Signal from baroreceptors to NTS then to CVLM.
4) CVLM signal to inhibit RVLM signals.
5) Sympathetic activity to heart and vessels decreases.
6) Lower sympathetic gives vasodilation and decreased BP

Question 19

Vagal parasympathetic outflow SA and AV nodes (4)

Answer 19

Vagal parasympathetic outflow SA and AV nodes:
• Loading of the baroreceptors also stimulates the vagus nerve which again activates the NTS.
• The signal from the NTS stimulates the nucleus ambiguous (vagal nuclei).
• Vagal parasympathetic impulses are sent to the heart and these have a depressor effect.
• Sinus tachycardia
o Inhibitory input from inspiratory centre.
o Each inhalation switches off nucleus ambiguous & HR increases.

Question 20

Sinus tachycardia 2

Answer 20

FC

Question 21

limbic stim of cardiac vagal activity 2

Answer 21

FC

Question 22

Cardiovascular afferents - stabilising blood pressure 6

Answer 22

FC