G3vi: Describe the cardiac reflexes

G3vi: 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
  1. BaroR
  2. ChemoR
  3. Bainbridge
  4. Bezold – Jarisch
  5. Cushing’s
  6. 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

  1. Stimulates resp centre
  2. ↑SNS
  3. ↑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:

  1. ↓HR
  2. ↓BP
  3. ↓SVR

Cushing’s

  • ↑HR
  • ↑BP
  • ↑FoC (to trigerminal & CAP)
  • BaroR
  • Reflex brady

Oculocarrdiac

  • ↓HR
  • ↓Foc
  • ↓BP