Lecture Notes: Baroreceptors and Blood Pressure Regulation

Introduction to Baroreceptors

• Definition:
  • Barrow (pressure/stretch) receptors are nerve cells that sense blood pressure through the stretch of blood vessel walls.
• Function:
  • Send information to the brain to help regulate blood pressure.

Types of Baroreceptors

1. Arterial Baroreceptors
   • Located in the blood vessel walls of the aortic arch and carotid sinus.
   • Nerve endings form cranial nerves:
     • Vagus nerve (10th cranial nerve): from aortic arch.
     • Glossopharyngeal nerve (9th cranial nerve): from carotid sinus.
2. Cardiopulmonary Baroreceptors
   • Found in walls of the right atrium, right ventricle, and pulmonary artery/veins.
   • Known as low-pressure or volume baroreceptors.

Mechanism of Arterial Baroreceptors

• Signal Transmission:
  • Synapse at the nucleus tractus solitarius in the medulla oblongata.
  • Information is relayed to cardiovascular centers.
• Cardiovascular Centers:
  • Located in the lower third of the pons and medulla oblongata.
  • Control sympathetic and parasympathetic branches of the autonomic nervous system.
  • Two main centers:
    • Vasomotor control center: Controls blood vessel diameter via sympathetic fibers (causes vasoconstriction).
    • Cardiac control center: Divided into:
      • Cardiac accelerator center: Increases heart rate and contractility.
      • Cardiac decelerator center: Decreases heart rate.

Baroreceptor Reflex (Baroreflex)

• Function: Adjusts blood pressure rapidly.
• Example Scenarios:
  • Increased Blood Pressure (e.g., running):
    • Increased firing of baroreceptors due to higher pressure.
    • Signals via glossopharyngeal and vagus nerves.
    • Inhibition of sympathetic system, stimulation of parasympathetic system.
    • Results in decreased cardiac output and peripheral resistance.
  • Decreased Blood Pressure (e.g., blood loss):
    • Decreased firing of baroreceptors due to lower pressure.
    • Stimulation of sympathetic system, inhibition of parasympathetic system.
    • Results in increased cardiac output and peripheral resistance.

Mechanism of Cardiopulmonary Baroreceptors

• Function: Regulate blood volume.
• Response to High Blood Volume:
  • Increased firing via vagus nerve.
  • Signal to hypothalamus to reduce vasopressin (ADH) production.
  • Stimulates atrial natriuretic peptide (ANP) secretion.
  • Increased heart rate and cardiac output.
• Response to Low Blood Volume:
  • Decreased firing.
  • Increased vasopressin production and reduced ANP secretion.
  • Reduced heart rate and cardiac output.

Summary

• Arterial Baroreceptors: Located in high-pressure areas, respond to blood pressure changes, and influence cardiac output and peripheral resistance.
• Cardiopulmonary Baroreceptors: Located in low-pressure areas, regulate blood volume via water and sodium excretion by the kidneys.