baroreflexer

The baroreflex, also known as the baroceptor reflex, is a rapid, short-acting reflex that, through the autonomic nervous system, helps maintain blood pressure homeostasis. It is primarily mediated by baroreceptors, which are stretch receptors located in the walls of the carotid sinuses and the aortic arch. These receptors sense changes in blood pressure.

When blood pressure increases, the baroreceptors are stretched more, leading to increased firing of afferent nerves to the brainstem. This stimulates the parasympathetic nervous system and inhibits the sympathetic nervous system. The result is a decrease in heart rate, vasodilation (widening of blood vessels), and reduced cardiac output, all of which work to lower blood pressure.

Conversely, when blood pressure decreases, the baroreceptors are stretched less, resulting in decreased firing. This leads to inhibition of the parasympathetic nervous system and stimulation of the sympathetic nervous system. The consequence is an increase in heart rate, vasoconstriction (narrowing of blood vessels), and increased cardiac output, which collectively work to raise blood pressure.

The baroreflex is crucial for maintaining blood pressure within a narrow range during everyday activities, such as standing up, which would otherwise cause a significant drop in blood pressure due to gravity. It acts as a buffer against transient fluctuations in blood pressure, ensuring adequate blood flow to vital organs. While effective for rapid adjustments, it is not the primary long-term regulator of blood pressure.