The Renin Angiotensin Aldosterone System RAAS Image Brady

The Renin. Angiotensin. Aldosterone System (RAAS) Image: Brady Urology (2014) Academic Portfolio Roll Number: 542 Word Count: 358

Functions RAAS is a complex endocrine negative feedback control system which controls blood pressure and fluid balance � Regulates systemic blood pressure by compensating for hypotension � Regulates renal blood flow � Regulates extracellular volume � Regulates sodium concentration Atlas (2007)

• Renin Components (Major components shown in yellow) - An enzyme produced and stored in the juxtaglomerular cells of the kidneys which converts angiotensinogen to angiotensin II • Angiotensinogen - An enzyme produced in the liver which causes vasoconstriction • Angiotensin I - A peptide hormone which acts as a precursor to angiotensin II • Angiotensin II - A peptide hormone which causes the release of aldosterone from the adrenals and increases blood pressure • Angiotensin-Converting-Enzyme (ACE) - An enzyme secreted by the lungs and kidneys which converts angiotensin I to angiotensin II • Aldosterone - A mineralocorticoid produced by the adrenal cortex which is involved in regulation of sodium, potassium and water balance • Anti-diuretic Hormone (ADH) - A hormone produced by the hypothalamus and released by the anterior pituitary gland, which stimulates reabsorption of water by the kidneys Goodman (2009)

Mechanisms In the kidneys, juxtaglomerular cells detect hypotension through signals received by the macula densa and convert pro-renin to renin Renin cleaves angiotensinogen to angiotensin I Angiotensin I enters the lungs and is converted to angiotensin II by ACE • • Angiotensin II causes: Vasoconstriction in arterioles decrease in blood flow & increase in blood pressure • Absorption of sodium and water in renal tubule increase in blood pressure • Increase in ADH secretion from pituitary water reabsorption • Increase in aldosterone secretion from adrenal glands Aldosterone causes: Principle cells in kidney to reabsorb sodium and water, and to secrete potassium increase in blood pressure • Alpha-intercalated cells in kidney to acidify urine using ATPase pump Atlas (2007)

Hypotension e. g. haemorrhage, dehydration Renin Angiotensinogen Hypertension - ACE Angiotensin II Other effects: Sympathetic Activity Na+ , Cl-, H 2 O reabsorption K- excretion Arteriolar vasoconstriction ADH secretion - Na+ , Cl-, H 2 O reabsorption - K- excretion Figure 1. The Renin-Angiotensin-Aldosterone System : This diagram represents the basic mechanisms of the pathway Aldosterone

Regulation • The system is initiated by the release of renin, which can be triggered by a number of ways: Ø Activation of the sympathetic nervous system Ø Renal artery hypotension Ø Reduced sodium delivery to the distal tubules of the kidney • The RAAS pathway is also modulated by natriuretic peptides (ANP and BNP) which are released by the heart • Therefore, this system is an important target for treatment of hypertension and heart failure Goodman (2009), Richards (1996)

References Atlas SA (2007). The Renin-Angiotensin Aldosterone System: Pathophysiological Role and Pharmacological Inhibition. Supplement to Journal of Managed Care Pharmacy. 13, 9 -20. Brady Urology (2014). Accessed at http: //bradyurology. blogspot. co. uk/2014_04_01_archive. html on 22 Feb 2015. Goodman HM (2009). Regulation of Salt and Water Balance. In: Basic Medical Endocrinology, 4 th Ed. pp 175 -195. USA: Elsevier Ltd. Richards AM (1996). The Renin-Angiotensin Aldosterone System and the Cardiac Natriuretic Peptides. Heart. 76, 36 -44