Question

what role do stretch receptors play when there is a larger than normal volume of blood returning to the heart from the veins?

Answer 1

Bainbridge Reflex

• Venous return : It is the blood flowing from veins back to the heart.
• Cardiac output : It is the blood pumped out by the heart.

Under normal condition venous return and cardiac output must be equal inorder to avoid accumulation of blood in pulmonary and systemic circulation.

Increased venous return causes increase blood volume in vena cava. Blood flow from the venacavas to the right atrium increased blood volume increases the pressure on atrium, This  stimulate the arterial stretch receptors or cardiac receptors located in venoatrial junction, causing an increase in firing of B fibers which signlas the  medullary control centers through vagas nerve. The efferent fibers will lead to a decrease in parasympathetic activity and increase in sympathetic activity. Decreased activity of parasympathetic system causes increase in contraction of heart or Trachycardia( increased heart rate) leading to  increase in cardiac output. Increased heart rate helps to pump more blood out of heart and inturn reducing the pressure on venacava.

It can also cause a  decrease in the secretion of Vasopressin . This will lead to an decreased reabsorption of glomerular filtrate causing an increase in  the urine output

They act antagositic to the baroreceptor mechanism to control the heart rate. Baroreceptors helps control the blood pressure and Bainbridge reflex helps control blood volume.

Baroreceptor mechanism

Baroreceptor are stretch receptors that are  located in the carotid sinus and aortic arch monitoring the blood pressure on a contious basis. Decrease in the blood pressure and volume may result in the inadequate amount of blood reaching in the peripheral organs and tissue, however increase in the volume and pressure beyond normal can cause damage to the blood vessels. Therefor monitoring blood pressure is important for maintaining normal function.