Cardiac circulation control Flashcards
What is a cardiac reflex
◦ “Reflex loops between the heart and central nervous system” which regulate heart rate and peripheral vascular resistance to maintain physiologic homeostasis
List the cardiac reflexes
4B’s 2C’s and a ROD
Bainbridge
Baroreceptor
Bezold Jarish
Barcroft Edholm
Chemoreceptor
Cushing
Respiratory sinus arrhythmia
Oculocardiac
Diving
What is the most important cardiac reflex
Baroreceptor
What are the 5 domains you need to consider for every reflex and every endocrine system
Sensor
Afferent
Processor
Efferent
Effector
Barorecepotr reflex
◦ Sensors: mechanoreceptors detect pressure (carotid sinus and aortic arch)
◦ Afferent: vagus and glossopharyngeal nerves
◦ Processor: nucleus of the solitary tract and nucleus ambiguus (vasomotor centre)in medulla oblongata
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: increased HR and BP (via SVR + increased stroke volume/cardiac output) in response to a fall in BP
Bainbridge reflex
◦ Afferent: vagus (atrial stretch) - increase in central venous pressure triggers low pressure mechanoreceptors in great veins and RA
◦ Processor: nucleus of the solitary tract and the caudal ventral medulla
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: increased RA pressure produces an increased heart rate;
Chemoreceptor reflex
◦ Afferent: carotid / aortic chemoreceptors (low PaO2 and/or high PaCO2) - in the context o response to MAP this will only occur under extreme hypotension
◦ Processor: nucleus of the solitary tract and nucleus ambiguus
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: bradycardia and hypertension in response to hypoxia
‣ (also secondary tachycardia from Bainbridge and Hering-Breuer reflexes)
Cushings reflex
◦ Afferent: mechanosensors in the rostral medulla?
◦ Processor: rostral ventrolateral medulla
◦ Efferent: sympathetic fibres to the heart and peripheral smooth muscle
◦ Effect: hypertension and baroreflex-mediated bradycardia
Bezold Jarish reflex
◦ Afferent: vagus (mechanical/chemical sttimuli to the cardiac chambers - ventricular) C fibres
◦ Processor: nucleus of the solitary tract
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: hypotension, coronary artery dilation and bradycardia
Oculocardiac reflex
◦ Afferent: trigeminal nerve (pressure to the globe of the eye)
◦ Processor: sensory nucleus of CN V; nucleus of the solitary tract
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: vagal bradycardia, systemic vasoconstriction, cerebral vasodilation
Diving reflex
◦ Afferent: trigeminal nerve (cold temperature; pressure of immersion)
‣ Processor: sensory nucleus of CN V; nucleus of the solitary tract
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: vagal bradycardia, systemic vasoconstriction, cerebral vasodilation
Barcroft Edholm reflex
◦ Afferent: emotional distress, hypovolaemia
◦ Processor: unknown
◦ Efferent: vagus nerve and sympathetic chain
◦ Effect: bradycardia, systemic vasodilation, hypotension
Respiratory sinus arrhtyhmia
◦ Afferent: central respiratory pacemaker
◦ Processor: nucleus ambiguus
◦ Efferent: vagus nerve, via the cardiac ganglion
◦ Effect: cyclical increase of heart rate during inspiration
What type of receptor is a baroreceptor? How are they activated?
- Baroreceptors are mechanoreceptors which respond to stretch stimuli.
- This strecth deforms mechanically sensitive sodium channels (DEG/ENaC, degenerin/epithelial sodium channels)
- With sufficient stimulus, sodium current increases to the point where the membrane potential reaches the threshold of local voltage-gated sodium channels, and generates a propagating action potential
Where are baroreceptors located
- Arterial baroreceptors (“high pressure baroreceptors”) are located at the junction of the intima and media of the aortic arch and carotid sinuses
◦ stretch sensitive mechanoreceptors
◦ Carotid sinus - small neurovascular structure in the adventitia in the dilated portion of the common carotid artery (carotid bulb) at its bifurcation. Not to be confused with the carotid body which is a PaO2/PaCO2 sesning chemoreceptor at the same location at the bifurcation of the vessels
◦ sinus senses stretch, and body senses breathing
◦ Aortic arch - medio-adventitial junction mainly confined to a saddle shaped area between the brchiocephalic trunk and the origin of the left subclavian
What layer of the vessel are baroreceptors in
- Arterial baroreceptors (“high pressure baroreceptors”) are located at the junction of the intima and media of the aortic arch and carotid sinuses
◦ stretch sensitive mechanoreceptors
◦ Carotid sinus - small neurovascular structure in the adventitia in the dilated portion of the common carotid artery (carotid bulb) at its bifurcation. Not to be confused with the carotid body which is a PaO2/PaCO2 sesning chemoreceptor at the same location at the bifurcation of the vessels
◦ sinus senses stretch, and body senses breathing
◦ Aortic arch - medio-adventitial junction mainly confined to a saddle shaped area between the brchiocephalic trunk and the origin of the left subclavian
Where is the carotid baroreceptor
- Arterial baroreceptors (“high pressure baroreceptors”) are located at the junction of the intima and media of the aortic arch and carotid sinuses
◦ stretch sensitive mechanoreceptors
◦ Carotid sinus - small neurovascular structure in the adventitia in the dilated portion of the common carotid artery (carotid bulb) at its bifurcation. Not to be confused with the carotid body which is a PaO2/PaCO2 sesning chemoreceptor at the same location at the bifurcation of the vessels
◦ sinus senses stretch, and body senses breathing
◦ Aortic arch - medio-adventitial junction mainly confined to a saddle shaped area between the brchiocephalic trunk and the origin of the left subclavian
Where is aortic baroreceptor
- Arterial baroreceptors (“high pressure baroreceptors”) are located at the junction of the intima and media of the aortic arch and carotid sinuses
◦ stretch sensitive mechanoreceptors
◦ Carotid sinus - small neurovascular structure in the adventitia in the dilated portion of the common carotid artery (carotid bulb) at its bifurcation. Not to be confused with the carotid body which is a PaO2/PaCO2 sesning chemoreceptor at the same location at the bifurcation of the vessels
◦ sinus senses stretch, and body senses breathing
◦ Aortic arch - medio-adventitial junction mainly confined to a saddle shaped area between the brchiocephalic trunk and the origin of the left subclavian
How does the baroreceptor receptor respond to changes in BP –> how does it convey the change to the controller
- Increased blood pressure (increased stretch, increased receptor firing rate)
- Decreased blood pressure (decreased receptor firing rate)
How does the carotid baroreceptor get to the central controller
- From the carotid sinus: carotid sinus nerve, a branch of the glossopharyngeal nerve - courses anteromedially to the internal carotid artery and joins the body of the glosspharngeal nerve at the base of the skull where its cell bodies lie in the petrosal ganglion
◦ Carotid sinus receptors are innervated by the sinus nerve of Hering, which is a branch of the glossopharyngeal nerve
How does the aortic baroreceptor get back to the central controller
- From the aortic arch: aortic nerve, a branch of the vagus nerve - cell bodies also in the petrosal ganglion which is in the jugular foramen where the nerves then synapse with NTS
- Both of these nerves travel through the jugular foramen to enter the medulla
◦ Both myelinated (A) and unmyelinated (C) fibres - fast response and baseline slower regulation
What is the processor of the baroreflex?
Nucleus of the solitary tract
* Sensory interneurons in the posteiror medulla (caudal ventrolateral medulla)
* Roles
◦ ANS
◦ Taste information - mediating cough and gag
◦ Middle ear - tympanic branch of CN9
What does the NTS do?
Nucleus of the solitary tract
* Sensory interneurons in the posteiror medulla (caudal ventrolateral medulla)
* Roles
◦ ANS
◦ Taste information - mediating cough and gag
◦ Middle ear - tympanic branch of CN9
What connections does the NTS have?
◦ Excitatory glutamate-mediated neurotransmission to the nucleus ambiguus translates the afferent signal into increased vagal activity
◦ GABA-ergic inhibitory neurons of the caudal ventral medulla translate the afferent signal into the inhibition of the rostral ventrolateral medulla (vasomotor centre - constant tonic output), which coordinates sympathetic tone
◦ Effrent fibres to the hypothalamus help coordinate the humoural response to changes in blood pressure.