Reflex control of CVS

Question 1

Cardiovascular reflexes

Answer 1

CVS responses to change through sensory/afferent pathways

Question 2

Excitatory inputs

Answer 2

Stimulation of reflexes - increase CO, TPR, BP - PRESSOR RESPONSE
E.g. arterial chemoreceptors, muscle metaboreceptors

Question 3

Inhibitory inputs

Answer 3

Stimulation of reflexes - decrease CO, TPR, BP - DEPRESSOR RESPONSE
E.g. arterial baroreceptors, cardiac pulmonary receptors

Question 4

Arterial baroreceptors

Answer 4

Sensors detect arterial wall stretch

Question 5

Where are arterial baroreceptors found

Answer 5

Sensors in walls of carotid arteries/aorta

Body monitors BP in carotid and coronary arteries

Question 6

Baroreceptors response to increase in pressure

Answer 6

Fast firing which eventually slows down and becomes constant, but at a higher level than before

Question 7

Baroreceptors response to decrease in pressure

Answer 7

Firing slows down proportionately

Question 8

Baroreceptors response to continuous alternating pressure

Answer 8

Threshold for baroreceptor activation can change

E.g - long term hypertension - baroreceptors become normalised at the new pressure and less activated

Question 9

Effect of decreased BP on baroreflex

Answer 9

• Increase sympathetic activity and decreased vagus activity
• Increase HR and CO
• Arteriole constriction = Increase TPR
• Venous constriction = increase CVP - increase SV and CO
• Increase blood vol. - vasoconstriction - decrease capillary pressure - increase absorption of interstitial fluid

Question 10

Veno-atrial mechanoreceptors

Answer 10

Stimulated by increase in cardiac filling/CVP

Increased sympathetic activity, tachycardia

Question 11

Ventricular mechanoreceptors

Answer 11

Stimulated by over distension of ventricles - depressor response
Weak reflex - mild vasodilation, lower blood pressure and preload

Question 12

Noiciceptive sympathetic afferents

Answer 12

mediate pain of angina & myocardial infarction. Reflex increased sympathetic activity – pale, sweaty, tachycardia of angina

Question 13

where are Arterial chemoreceptors located

Answer 13

Carotid and aortic bodies

Question 14

What do arterial chemoreceptors do

Answer 14

Regulate ventilation and drive cardiac reflexes during asphyxia (low O2/high CO2) shock and haemorrhage

Question 15

What stimulates arterial chemoreceptors

Answer 15

Low O2, high CO2, H+, K+

Question 16

Pressor response of arterial chemoreceptors

Answer 16

Increased sympathetic activity
Tachycardia, increases selective arterial/venous constriction
Increased cardiac out put and blood pressure - especially preservation of cerebral blood flow

Question 17

Muscle metaboreceptors

Answer 17

Sensory fibres in group IV motor fibres located in skeletal muscle
Activated by metabolites K+, lactate, adenosine

Question 18

Pressor response of muscle metaboreceptors

Answer 18

• Increase sympathetic activity
• Tachycardia, increase arterial/venous constriction
• Increase cardiac output/blood pressure

Question 19

Central role of the nucleus tractus solitarius (NTS)

Answer 19

1) Signal from baroreceptor afferent fibres enter NTS
2) Sends information to the CVLM
3) CVLM sends inhibitory information to the RVLM
4) Results in inhibiton of sympathetic efferent nerves to heart and vessels
5) Less sympathetic efferent signals result in reduction in HR, less vasoconstriction, lower BP

Question 20

Experimental link between CVLM and RVLM

Answer 20

1) Intravenous phenylphrine (α1 agonist increases TPR and BP).
2) BP rises and loads baroreceptors (carotid & aortic)
3) Signal from baroreceptor 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 lowers BP

Question 21

Vagal and parasympathetic outflow SA and AV nodes stimulation

Answer 21

Loading of the baroreceptors stimulates the vagus nerve which activates the NTS
Signal from NTS stimulates the nucleus ambiguous (vagal nuclei)
Vagal parasympathetic impulses are sent to the heart and these have a depressor effect

Question 22

Sinus tachycardia

Answer 22

Inhibitory input from inspiratory centre

Each inhalation switches off nucleus ambiguous and HR increases slightly

Question 23

What happens when afferent fibres form baroreceptors are removed

Answer 23

Arterial pressure varies enormously - all different

Question 24

What happens when afferent fibres from cardiac receptors are removed

Answer 24

Arterial pressure varies and the means become different

Question 25

What happens when the arterial pressure falls to 50mmHg

Answer 25

Insufficient perfusion to end organs

Question 26

what happens when the arterial pressure rises to 150mmHg

Answer 26

Damage the CVS