FRCEM Primary: Core Physiology: Hormones and renal blood flow

Question.

Renal blood flow is increased by which one of the following set of circulating hormones?

a. Dopamine and angiotensin II

b. Dopamine and renin

c. Angiotensin II and renin

d. Prostaglandins and angiotensin

e. Prostaglandins and dopamine

 

 

Answer.

The correct answer is e. Dopamine and prostaglandins both increase renal blood flow.

Explanation.

Renal blood flow is highly auto regulated and maintained at about 25% of cardiac output (or 1.2-1.3L/min for a 70kg adult). Renal blood flow depends on renal vascular resistance as well as on systemic arterial and venous pressures.

Circulating factors which increase renal blood flow include:

  • Dopamine: Vasodilation of renal vessels
  • Prostaglandins: Increases renal blood flow by vasodilating afferent* arterioles particularly at times of renal hypoperfusion (hence the nephrotoxic effect of NSAIDS which inhibit prostaglandin synthesis)
  • Atrial natriuretic peptide (ANP) also vasodilates afferent renal vessels to promote promote glomerular filtration and reduce blood volume.

Those which reduce renal blood flow include:

  • Angiotensin II: Vasoconstriction of both afferent and efferent arterioles*, though with greater effect on efferent vessels to increase glomerular filtration
  • Norepinephrine: Vasoconstriction.

Local factors: CO2, lactate, H+, K+, hypoxia all vasodilation renal vessels and increase renal blood flow.

[* afferent arterioles branch from the renal artery and supply blood to the glomerulus; efferent arterioles remove blood from the glomerulus and supply it to the capillaries of the renal medulla (vasa recta) and renal cortex.]

 

 

 

 

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