Reflex control of CVS Flashcards
Cardiovascular reflexes
CVS responses to change through sensory/afferent pathways
Excitatory inputs
Stimulation of reflexes - increase CO, TPR, BP - PRESSOR RESPONSE
E.g. arterial chemoreceptors, muscle metaboreceptors
Inhibitory inputs
Stimulation of reflexes - decrease CO, TPR, BP - DEPRESSOR RESPONSE
E.g. arterial baroreceptors, cardiac pulmonary receptors
Arterial baroreceptors
Sensors detect arterial wall stretch
Where are arterial baroreceptors found
Sensors in walls of carotid arteries/aorta
Body monitors BP in carotid and coronary arteries
Baroreceptors response to increase in pressure
Fast firing which eventually slows down and becomes constant, but at a higher level than before
Baroreceptors response to decrease in pressure
Firing slows down proportionately
Baroreceptors response to continuous alternating pressure
Threshold for baroreceptor activation can change
E.g - long term hypertension - baroreceptors become normalised at the new pressure and less activated
Effect of decreased BP on baroreflex
- 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
Veno-atrial mechanoreceptors
Stimulated by increase in cardiac filling/CVP
Increased sympathetic activity, tachycardia
Ventricular mechanoreceptors
Stimulated by over distension of ventricles - depressor response
Weak reflex - mild vasodilation, lower blood pressure and preload
Noiciceptive sympathetic afferents
mediate pain of angina & myocardial infarction. Reflex increased sympathetic activity – pale, sweaty, tachycardia of angina
where are Arterial chemoreceptors located
Carotid and aortic bodies
What do arterial chemoreceptors do
Regulate ventilation and drive cardiac reflexes during asphyxia (low O2/high CO2) shock and haemorrhage
What stimulates arterial chemoreceptors
Low O2, high CO2, H+, K+
Pressor response of arterial chemoreceptors
Increased sympathetic activity
Tachycardia, increases selective arterial/venous constriction
Increased cardiac out put and blood pressure - especially preservation of cerebral blood flow
Muscle metaboreceptors
Sensory fibres in group IV motor fibres located in skeletal muscle
Activated by metabolites K+, lactate, adenosine
Pressor response of muscle metaboreceptors
- Increase sympathetic activity
- Tachycardia, increase arterial/venous constriction
- Increase cardiac output/blood pressure
Central role of the nucleus tractus solitarius (NTS)
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
Experimental link between CVLM and RVLM
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
Vagal and parasympathetic outflow SA and AV nodes stimulation
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
Sinus tachycardia
Inhibitory input from inspiratory centre
Each inhalation switches off nucleus ambiguous and HR increases slightly
What happens when afferent fibres form baroreceptors are removed
Arterial pressure varies enormously - all different
What happens when afferent fibres from cardiac receptors are removed
Arterial pressure varies and the means become different
What happens when the arterial pressure falls to 50mmHg
Insufficient perfusion to end organs
what happens when the arterial pressure rises to 150mmHg
Damage the CVS
