Question

Explain the negative feedback loop between baroreceptors, the cardiovascular (CV) center, and the heart. Address: dropping blood pressure, heart stimulation, and hormonal vessel constriction. How do these all work together to achieve homeostasis?

Answer 1

A negative feed back system reverses a change in the controlled condition. The negative feed back mechanism between baroreceptors, the cardiovascular center and the heart plays an important role in controlling the blood pressure and there by maintaining the homeostasis. The baroreceptors receptors are specialised stretch receptors which are located with in the areas of blood vessels and the heart chambers. These receptors respond to degree of stretch caused by the presence of blood. In case of drooping blood pressure , the degree of stretch in the baroreceptors is lowered which would result in an increase in sympathetic stimulation to the heart. This causes an increase in cardiac output. This also triggers sympathetic stimulation of the peripheral vessels which results in vaso constriction thereby increase in the blood pressure and maintaining homeostasis. This forms the negative feedback loop between baroreceptors, CV center and the heart.

The feed back loop also involves endocrine regulation which is caused by changes in blood volume or by the stimulation of the heart. Endocrine regulation is brought about by catecholamines, epinephrine, nor epinephrine, and hormones ADH, erythropoieitin and renin angiotenisn mechanisms.

• sympathetic activation causes adrenal glands to release epinephrine, norepinephrine which in turn increase the cardiac output and peripheral vasoconstriction resulting in an increase in blood pressure.
• Kidney in response to decrease in blood pressure / volume produces renin and erythropoietin.
  • Renin causes activation of angiotensin II which stimulates release of Anti Diuretic hormone (ADH) and aldosterone by adrenal cortex which results in increase in blood volume thereby raising the blood pressure.
  • Erythropoietin causes increase in red blood cell formation there by incresing the blood volume and restoring homeostasis

when the homeostatsis is achieved the feed back loop stops and normal conditions are retrived.