G3vii: Describe the cardiac reflexes
Cardiac Reflexes
- Definition: a fast-acting loop between H & CNS
- Consists of:
- Afferent Sensor (monitors cardiac function) in atria, ventricles, CA, great vessels
→ Control (CNS)
→ Effector organ (ANS)
- Function: to maintain constant CO & critical organ perfusion
- The 6 Cardiac Reflexes
- BaroR
- ChemoR
- Bainbridge
- Bezold – Jarisch
- Cushing’s
- Oculocardiac
Reflex Sensor
Afferents
Baroreceptor Stretch
Baroreceptors in aortic arch
Carotid sinus
Chemoreceeptor Chemo
Carotid + aortic bodies
Bainbridge Stretch
RA wall
Cavoatrial junction
Bezold-Jarisch Chemo & Mechano
Ventricle wall
Unmyelinated Type C fibres
Cushing’s
CNS
Oculocarrdiac
Extra-ocular muscle & globe
Reflex Sensor
Stimulators
Baroreceptor Stretch
↑Transluminal pressure
Chemoreceeptor Chemo
pO2 <80
pO2 >40
pH <7.4
Bainbridge Stretch
Stretch
↑filling
Bezold-Jarisch Chemo & Mechano
Noxious stimuli
Cushing’s
Ischaemia 2° ↑ ICP
Oculocarrdiac
↑pressure
Reflex Sensor
Control
Baroreceptor Stretch
Via glossoph. (carotid)
Vagus (arch) to CV Centre of Medulla
Chemoreceeptor Chemo
Via glossoph. (carotid)
Vagus (aortic) to CV Centre of Medulla
Bainbridge Stretch
Via vagus (X) to CV Centre in CNS
Bezold-Jarisch Chemo & Mechano
Medulla vasomotor centre
Cushing’s
Direct symp. stimulation of vasomotor centre
Oculocarrdiac
Ciliary nerve to Trigeminal
Reflex Sensor
Efferent
Baroreceptor Stretch
NEGATIVE FEEDBACK inhibits symp. & ↑parasymp. nerves
Chemoreceeptor Chemo
- Stimulates resp centre
- ↑SNS
- ↑catecholamine release from Adrenal Medulla
Bainbridge Stretch
PNS inhibition = ↑HR
Directly stimulates SA node = ↑HR,↑ANS, ↓ADH
Bezold-Jarisch Chemo & Mechano
↑PNS activity
Cushing’s
MASS SYMP. STIMULATION
Oculocarrdiac
Vagus
↑PNS
Reflex Sensor
Overall effect
Baroreceptor Stretch
@Heart
- ↓HR
- ↓FoC
- ↓CO
@Vessels
- ↓VR
- ↓venous/ arterial tone
Chemoreceeptor Chemo
- ↑MV
- ↑HR
- ↑FoC
- VD CA
- ↑SVR
Bainbridge Stretch
- ↑HR
- ↑NaCl/H2O excretion
- ↑urine output
Bezold-Jarisch Chemo & Mechano
Triad of:
- ↓HR
- ↓BP
- ↓SVR
Cushing’s
- ↑HR
- ↑BP
- ↑FoC (to trigerminal & ↑CAP)
- BaroR
- Reflex brady
Oculocarrdiac
- ↓HR
- ↓Foc
- ↓BP