Reflex Control of the Circulation
This session will cover:
Arterial baroreceptors and the baroreflex
The role of cardiopulmonary receptors
The chief reflex effects of baroreceptors activation/inhibition and
role of the baroreflex (eg in the response to haemorrhage or
clinical shock)
The location and reflex effects of peripheral arterial
chemoreceptors
The role of muscle metaboreceptors
The meaning of 'alerting (stress) response'
The CVS has various types of sensory receptors:
Arterial baroreceptors – Are linked to a decrease in BP (a depressor response,
reducing HR, force of contraction, causing vasodilation)
Cardiac stretch receptors – Have mixed actions, some decrease BP, some increase
Arterial chemoreceptors – Increase BP (pressor response – switch on sympathetics)
Muscle metaboreceptors – Increase BP (pressor response – switch on sympathetics)
These receptors provide information via afferents to -> central pathways
Central Pathways
- Medulla relay station (nucleus tractus solitaries) --> relays info from receptors to
other parts of the body
- Vagal motor neurones (nucleus ambiguus)
- Pre-sympathetic neurones (rostro-ventral-lateral medulla, RVLM)
The effects on BP via sympathetic and vagus nerves
Heart --> Changes in heart rate and contractility
Resistance vessels --> TPR
Veins --> Contractility of veins hence CVP (will effect Starling’s law)
These connections can be summarised in the diagram below:
, As can be seen we have excitatory inputs from arterial chemoreceptors and muscle
work receptors to the medulla which modulates the info and sends information via
vagus or sympathetic nerves to control venous tone, heart rate and SV or resistance
vessel tone. These will change the variables controlling BP of CO and TPR hence we
will get a change in BP.
There are also inhibitory inputs to the medulla via the cardiac receptors and arterial
baroreceptors which switch off this pathway.
The Baroreflex
The baroreflex is very important to maintain blood flow to the brain and
myocardium, but we are not measuring blood flow to these organs – there are no
blood flow sensors.
What we do is we measure pressure and we do this by looking at the amount of
stretch in the carotid and coronary arteries or aorta.
The carotid arteries perfuse the brain so by having blood pressure sensors in the
walls measuring pressure changes this info can inform the brain of these changes.
We also have them in the aorta (tells brain about pressure changes in coronary
circulation). These sensors detect wall stretch and are called baroreceptors
The arterial baroreceptors are located in the carotid sinus and in the aorta. The ends
of the receptors are spread out over the area of blood vessel and send info (via
impulse frequency) back to the NTS.
This session will cover:
Arterial baroreceptors and the baroreflex
The role of cardiopulmonary receptors
The chief reflex effects of baroreceptors activation/inhibition and
role of the baroreflex (eg in the response to haemorrhage or
clinical shock)
The location and reflex effects of peripheral arterial
chemoreceptors
The role of muscle metaboreceptors
The meaning of 'alerting (stress) response'
The CVS has various types of sensory receptors:
Arterial baroreceptors – Are linked to a decrease in BP (a depressor response,
reducing HR, force of contraction, causing vasodilation)
Cardiac stretch receptors – Have mixed actions, some decrease BP, some increase
Arterial chemoreceptors – Increase BP (pressor response – switch on sympathetics)
Muscle metaboreceptors – Increase BP (pressor response – switch on sympathetics)
These receptors provide information via afferents to -> central pathways
Central Pathways
- Medulla relay station (nucleus tractus solitaries) --> relays info from receptors to
other parts of the body
- Vagal motor neurones (nucleus ambiguus)
- Pre-sympathetic neurones (rostro-ventral-lateral medulla, RVLM)
The effects on BP via sympathetic and vagus nerves
Heart --> Changes in heart rate and contractility
Resistance vessels --> TPR
Veins --> Contractility of veins hence CVP (will effect Starling’s law)
These connections can be summarised in the diagram below:
, As can be seen we have excitatory inputs from arterial chemoreceptors and muscle
work receptors to the medulla which modulates the info and sends information via
vagus or sympathetic nerves to control venous tone, heart rate and SV or resistance
vessel tone. These will change the variables controlling BP of CO and TPR hence we
will get a change in BP.
There are also inhibitory inputs to the medulla via the cardiac receptors and arterial
baroreceptors which switch off this pathway.
The Baroreflex
The baroreflex is very important to maintain blood flow to the brain and
myocardium, but we are not measuring blood flow to these organs – there are no
blood flow sensors.
What we do is we measure pressure and we do this by looking at the amount of
stretch in the carotid and coronary arteries or aorta.
The carotid arteries perfuse the brain so by having blood pressure sensors in the
walls measuring pressure changes this info can inform the brain of these changes.
We also have them in the aorta (tells brain about pressure changes in coronary
circulation). These sensors detect wall stretch and are called baroreceptors
The arterial baroreceptors are located in the carotid sinus and in the aorta. The ends
of the receptors are spread out over the area of blood vessel and send info (via
impulse frequency) back to the NTS.
