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Efferent arteriole

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Title: Efferent arteriole  
Author: World Heritage Encyclopedia
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Subject: Afferent arterioles, Nephron, Hyaline arteriolosclerosis, Interlobular arteries, Interlobar veins
Collection: Kidney Anatomy
Publisher: World Heritage Encyclopedia

Efferent arteriole

Efferent arteriole
Scheme of renal tubule and its vascular supply. (Label "Efferent vessel" is visible in upper left.)
Distribution of bloodvessels in cortex of kidney.
Latin arteriola glomerularis efferens capsulae renalis
glomerular capillaries
Gray's p.1221
Anatomical terminology

The efferent arterioles are capillaries of the glomerulus. They play an important role in maintaining the glomerular filtration rate despite fluctuations in blood pressure.

In the mammalian kidney they follow two markedly different courses, depending on the location of the glomeruli from which they arise.

In the mammalian kidney about 15% of glomeruli lie close to the boundary between the renal cortex and renal medulla and are known as juxtamedullary glomeruli. The rest are simply undifferentiated cortical glomeruli.


  • In undifferentiated cortical glomeruli 1
  • In juxtamedullary glomeruli 2
  • Regulation of glomerular filtration rate 3
  • See also 4
  • Additional images 5
  • External links 6

In undifferentiated cortical glomeruli

The efferent arterioles of the undifferentiated cortical glomeruli are the most complex. Promptly on leaving the glomerulus they break up into capillaries and become part of a rich plexus of vessels surrounding the cortical portions of the renal tubules.

In juxtamedullary glomeruli

The efferent arterioles of the juxtamedullary glomeruli are much different. They do break up, but they form bundles of vessels (arteriolae recti) that cross the outer zone of the medulla to perfuse the inner zone.

Vessels returning from the inner medulla (rete mirabile.

This rete is responsible for the osmotic isolation of the inner medulla from the rest of the kidney and so permits the excretion of a hypertonic urine when circumstances require. Interestingly, since the rete also isolates the inner medulla from gaseous exchange, any metabolism in this area is anaerobic, and red cells, which would serve no purpose there, are ordinarily shunted from the arteriolae recti by an unknown mechanism into the capillary plexus surrounding the tubules of the outer zone of the medulla.

Blood in this plexus and returning from the inner medulla finds its way to the renal vein and the general circulation by pathways similar to those providing drainage for the rest of the cortex.

Regulation of glomerular filtration rate

When angiotensin II levels are increased due to activation of the renin-angiotensin-aldosterone system, most of the arteries in the body experience vasoconstriction, in order to maintain adequate blood pressure. However, this reduces blood flow to the kidneys. To compensate, the efferent arterioles constrict to a greater degree than the other arteries, in response to increased levels of angiotensin II. Pressure in glomerular capillaries is therefore maintained and glomerular filtration rate remains adequate.

See also

Afferent arteriole

Additional images

External links

  • Physiology at MCG 7/7ch03/7ch03p10
  • Anatomy photo: Urinary/mammal/vasc0/vasc3 - Comparative Organology at University of California, Davis - "Mammal, renal vasculature (EM, Low)"
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