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Renin Angiotensin Aldosterone System (RAAS) review

RAAS Review 
It’s critical to understand RAAS for critically ill/traumatically injured shock patients. The RAAS regulates blood pressure and fluid balance in the body. When blood volume or sodium levels in the body are low, or potassium is high, cells in the kidney release the enzyme, renin. Renin converts angiotensinogen, which is produced in the liver, to the hormone angiotensin I. An enzyme known as ACE or angiotensin-converting enzyme found in the lungs metabolizes angiotensin I into angiotensin II. Angiotensin II causes blood vessels to constrict and blood pressure to increase. Angiotensin II stimulates the release of the hormone aldosterone in the adrenal glands, which causes the renal tubules to retain sodium and water and excrete potassium. Together, angiotensin II and aldosterone work to raise blood volume, BP and sodium levels in the blood to restore the balance of sodium, potassium, and fluids in an attempt to normalize the BP in an otherwise “shocky” patient.


Hypovolemic shock occurs due to loss of in total volume of blood, available for circulation. Whether the bleeding is caused by blunt or penetrating trauma, the loss of blood stimulated baroreceptors in the carotid bodies and aortic arch to speed up the HR. HR X SV=CO.



When pts are trying to compensate hypovolemic shock, RAAS (Renin angiotensin aldosterone system) is activated.
The activated RAAS system releases angiotensin II. Angiotensin II causes vasoconstriction of arteries and veins, thereby increasing blood pressure. It also promotes adrenal cortex to secrete aldosterone. Aldosterone in turn stimulates sodium and water retention as well as excretion of potassium from kidneys. The resulting high sodium ions in the serum causes secretion of ADH (antidiuretic hormone). ADH intensifies water reabsorption, resulting in increased blood volume, BP (blood pressure) and CO (cardiac output). This is why we frequently see our hypovolemic trauma patients present with tachycardia and hypotension, depending on which stage of shock they present with. 
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