Baroreceptor Reflex

High Pressure Baroreceptor (HP BR)

• Carotid sinus and aortic arch receptors
  • Detects > 5-10 % change in plasma volume
  • ↓ Plasma volume → Increased central SNS tone and decreased PSNS tone
• Sensor:
  • Stretch receptor: ↑ distension of vessel → ↑ discharge rate
  • Threshold > 60mmHg → normally has baseline tone.
  • Located at Carotid Sinus and Aortic Arch
  • Spray like visceral nerve endings
  • Transmitted by:
    • Unmyelinated C-fibres (most receptors)
    • Myelinated A-fibres (↑ sensitivity at lower BP)
    • Individual fibres have narrow BP range
  • Increased reponsiveness to pulsitile rather than continuous flow
• Afferent signal:
  • Carotid sinus → Nerve of Hering → CN9
  • Aortic Arch → CN10 → NTS
  • Both then divide to:
    • Stimulatory afferents → ↑ Medullary vagal outflow
    • Inhibitory afferents → ↓ RVLM SNS outflow
• Outcome:
  • ↑’d distension → ↓’d HR/Contractility/SVR
  • Provides strict negative feedback to Δ’s in CO

Low Pressure Baroreceptors (LP BR)

• Location
  • Located at junction of return vessels and atria, vetricular walls, pulmonary vessles
  • Throughout the peripheral vasculature (esp kidney)
• Sensor:
  • Stretch receptor: ↑ distension of vessel → ↑ discharge rate
  • Detect > 10% decrease in plasma volume as decreased atrial stretch
  • ↓ Discharge rate with
    • Reduced ANP release
    • Increase SNS output
• 2 types
  • A receptors → fire at atrial contraction (a wave)
  • B type → fire at atrial filling (v wave)
• Outcome
  • ↓ PL → ↓ CO → ↓BR discharge rate
    • Medulla afferents cause
      • ↓ SNS (NA) and ↑PSNS (RVLM) outflow → peripheral vascular vaso and venodilation
      • ↓ SNS activity to kidney → ↓ Na/H2O conservation
      • ↑ SNS activity to sinus node
    • Hypothalamic afferents cause
      • → ↓ ADH release and ↓ Thirst
  • ↑ contractility/HR/SV/CO
  • ↑ SVR → autotransfusion and ↑ perfusing pressure (but ↑AL)

Gladwin 2016

Answer by Gladwin