Updated: 12/29/2019

Renin-Angiotensin-Aldosterone System

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Overview
 


Introduction
  • The renin-angiotensin-aldosterone system (RAAS) attempts to maintain arterial blood pressure by controlling blood volume
    • a decrease in arterial blood pressure is sensed by the kidneys as decreased renal perfusion pressure
      • this in turn stimulates the juxtaglomerular cells to secrete renin into circulation
        • note that increased sympathetic activity and β1-agonists (e.g., isoproterenol) increase renin secretion
        • renin converts angiotensinogen into angiotensin I, a precursor of angiotensin II
          • angiotensin-converting enzyme (ACE) in the lung and kidneys converts angiotensin I → angiotensin II
      • note that a decrease in Na+ delivery to the macula densa also stimulates RAAS
    • angiotensin II activates type I G protein-coupled angiotensin II receptors (AT1) receptors which
      • acts on the adrenal cortex (zona glomerulosa) to increase aldosterone secretion
        • aldosterone will increase Na+ reabsorption and K+ secretion in the principal cells of the distal tubule and collecting duct 
        • aldosterone will also increase H+ secretion in the alpha-intercalated cells 
      • directly stimulates the Na+-H+ exchange 
      • acts on the hypothalamus to increase thirst and the pituitary to increase anti-diuretic hormone (ADH) secretion
        • ADH will act on the principal cells to increase aquaporin-2 expression
          • this increases the collecting duct's permeability to water and thus increases water reabsorption
      • acts on arterioles to increase total peripheral resistance and thus increasing arterial pressure
      • preferrentially constricts the efferent arteriole to maintain glomerular filtration rate (GFR) in low volume states (e.g., hemorrhaging)
 
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(M1.RL.15.4671) A researcher is testing an unknown compound, X, and seeing the effect it has on renal function. When she applies compound X to the cells, she finds that the urinary concentration of sodium and the pH decreases while the urinary potassium increases. Which of the following correctly states:
1) the cells of the kidney this compound acts on and
2) the identity of compound X?
Tested Concept

QID: 107159
1

Distal convoluted tubule; atrial natriuretic peptide

3%

(3/108)

2

Loop of Henle; furosemide

10%

(11/108)

3

Distal convoluted tubule; hydrochlorothiazide

11%

(12/108)

4

Principal cells; aldosterone

53%

(57/108)

5

Principal cells; spironolactone

19%

(21/108)

M 2 D

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