Final answer:
Baroreceptors are specialized stretch receptors located within blood vessels and heart chambers that respond to the degree of stretch caused by blood. During hypotension, baroreceptors detect the decrease in blood pressure and initiate a reflex response to increase the blood pressure.
Step-by-step explanation:
Baroreceptors are specialized stretch receptors located within thin areas of blood vessels and heart chambers that respond to the degree of stretch caused by the presence of blood. They send impulses to the cardiovascular center to regulate blood pressure. Vascular baroreceptors are found primarily in sinuses (small cavities) within the aorta and carotid arteries: The aortic sinuses are found in the walls of the ascending aorta just superior to the aortic valve, whereas the carotid sinuses are in the base of the internal carotid arteries. There are also low-pressure baroreceptors located in the walls of the venae cavae and right atrium.
During hypotension (low blood pressure), the baroreceptors detect the decrease in blood pressure and initiate a reflex response to increase the blood pressure. The rate of baroreceptor firing decreases, and the cardiovascular center increases sympathetic stimulation and decreases parasympathetic stimulation. This leads to vasoconstriction (narrowing of blood vessels) and an increase in heart rate and contractility, all of which help raise the blood pressure and restore homeostasis.