What Happens When Baroreceptors Are Stimulated?

Baroreceptors are stretch-sensitive mechanoreceptors located primarily in the carotid sinuses and aortic arch. They continuously monitor arterial blood pressure and provide feedback to the brain to maintain blood pressure homeostasis through the baroreflex.

• When blood pressure rises, the arterial walls stretch more, leading to increased baroreceptor firing.

• This increased firing signals the brainstem (medulla oblongata) to reduce sympathetic nervous system activity and increase parasympathetic outflow.

• The resulting physiological effects include:

  • Bradycardia: Reflex slowing of heart rate through increased parasympathetic (vagal) tone.

  • Hypotension: Because vasodilation (relaxation of arterial smooth muscle) reduces peripheral resistance, lowering blood pressure.

  • Venodilation: Venous dilation reduces venous return and preload, helping reduce cardiac output and blood pressure.

These responses combine to lower elevated blood pressure rapidly.

What Does NOT Occur?

• Vasoconstriction does NOT occur upon baroreceptor stimulation when blood pressure is high.

• Instead, sympathetic inhibition causes vasodilation to decrease blood pressure.

• Vasoconstriction is a response to decreased baroreceptor activity, i.e., when blood pressure falls and sympathetic outflow increases.

Summary Table

Conclusion

The correct answer to the question:

Which one of the following does NOT occur due to stimulation of baroreceptors?

(4) Vasoconstriction

Baroreceptor stimulation inhibits sympathetic activity leading to vasodilation, not vasoconstriction, as part of the negative feedback loop maintaining blood pressure within normal range.

Additional Insights

This negative feedback loop helps prevent excessive rises in blood pressure and protects vital organs from hypertensive damage. Understanding this reflex is fundamental in cardiovascular physiology and clinical settings such as managing hypertension and syncope.