In: Anatomy and Physiology
Explain the neural, renal, and hormonal regulation of blood pressure.
Ans:
Blood pressure is defined as pressure exerted by blood on the walls of the blood vessels. It is regulated through various mechanism in the body.
(i) Neural regulation of blood pressure: It is the short term regulation of blood pressure which is achieved through the role of cardiovascular centers and baroreceptor stimulation.
(ii) Renal regulation of blood pressure: The kidney plays a central role in the regulation of arterial blood pressure. The kidney influences blood pressure by causing the arteries and veins to constrict and also by increasing the circulating blood volume. Upon constriction of blood vessels, the increase in resistance to blood flow causes increase in blood pressure. The increased Na and water reabsorption from the distal tubules reduces urine output and increases the circulating blood volume. The increased blood volume helps stretch the heart muscle and generate more pressure with each beat, thereby increasing the blood pressure. There are three mechanisms of renal regulation for control of blood pressure by:
(iii) Hormonal regulation of blood pressure: The hormonal control mechanism of blood pressure involves renin-angiotensin-aldosterone system (RAAS) of kidneys to regulate blood volume. It is a long-term regulation of blood pressure. The juxtaglomerular cells in the kidneys secrete renin into the blood in response to decreased blood pressure. Renin facilitates the conversion of angiotensinogen to angiotensin I, which is then converted to angiotensin II using angiotensin converting enzyme (ACE). Angiotensin II is a potent vasoconstrictor. It acts directly on kidneys to increase sodium reabsorption in proximal convoluted tubules. Angiotensin II further promotes the stimulation of aldosterone. Aldosterone promotes salt and water retension by acting at the distal tubule to increase expression of epithelial sodium channels. Further, aldosterone increases the activity of basolateral Na+-K+ ATPase, thus increasing the electrochemical gradient for movement of sodium ions. This ultimately results in decreased water excretion, increases blood volume and blood pressure.
Another mechanism of regulating blood pressure is by release of anti-diuretic hormone (ADH) from hypothalamus in resonse to thirst or high plasma osmolarity. Prostaglandins acts as a local vasodilators to increase GFR and reduce sodium reabsorption to control blood pressure.