Changes

Hormonal responses exist for the purpose of both lowering and raising blood pressure. They act in various ways, including vasoconstriction, vasodilation and alteration of blood volume.

Hormonal responses exist for the purpose of both lowering and raising blood pressure. They act in various ways, including vasoconstriction, vasodilation and alteration of blood volume.

[[Renin Angiotensin Aldosterone System|'''Renin-Angiotensin-Aldosterone System''' (RAAS)]]:

====Renin-Angiotensin-Aldosterone System (RAAS)====

The juxtaglomerular apparatus of the kidneys plays an important role in the control of blood volume and blood pressure - renin is released from this area. The stimulus for renin release into the circulation includes; local baroreceptors in afferent renal arteriole - a drop in renal blood flow stimulates renin release; cardiac and arterial baroreceptors (in response to reduced local perfusion) - beta-1 mediated effect via innervation of the juxtaglomerular apparatus (JGA); decreased chloride delivery to the macula densa (detected by chemoreceptors) - a drop in glomerular filtration rate (GFR) leads to increased reabsorption in the proximal convoluted tubule, that is sensed as a drop in chloride presented at the macula densa. Renin then leads to the cleavage of circulating Angiotensinogen (produced by the liver) to angiotensin I, and then angiontensin converting enzyme (ACE) catalyses the production of angiotensin II from angiotensin I - this occurs mainly in the lungs. ACE is bound to endothelial cells throughout the vascular system. Angiotensin II acts as a stimulus to aldosterone release from the zona glomerulosa of the adrenal cortex, which in turn leads to sodium and water retention in the cortical collecting duct of the renal tubule.

The juxtaglomerular apparatus of the kidneys plays an important role in the control of blood volume and blood pressure - renin is released from this area. The stimulus for renin release into the circulation includes;  

*local baroreceptors in the afferent renal arteriole - a drop in renal blood flow stimulates renin release

*cardiac and arterial baroreceptors responsd to reduced local perfusion - beta-1 mediated effect via innervation of the juxtaglomerular apparatus (JGA)  

*decreased chloride delivery to the macula densa is detected by chemoreceptors - a drop in glomerular filtration rate (GFR) detected as a drop in chloride presented at the macula densa leads to increased reabsorption in the proximal convoluted tubule.

 

Renin then leads to the cleavage of circulating Angiotensinogen (produced by the liver) to angiotensin I, and then angiontensin converting enzyme (ACE) catalyses the production of angiotensin II from angiotensin I - this occurs mainly in the lungs. ACE is bound to endothelial cells throughout the vascular system. Angiotensin II acts as a stimulus to aldosterone release from the zona glomerulosa of the adrenal cortex, which in turn leads to sodium and water retention in the cortical collecting duct of the renal tubule.

'''NOTE''' This system is responsible for the long-term maintenance of blood pressure, but is also activated very rapidly in the presence of hypotension.

'''NOTE''' This system is responsible for the long-term maintenance of blood pressure, but is also activated very rapidly in the presence of hypotension.