Efferent arteriole
Arteriola glomerularis efferens
Also known as: efferent glomerular arteriole
The arteriole that drains the glomerulus and leads to a second capillary bed (peritubular capillaries or vasa recta); its resistance maintains high glomerular pressure and is preferentially raised by angiotensin II.
Overview
Unusually, the glomerular capillaries drain into an arteriole rather than a venule. The efferent arteriole leaves the renal corpuscle at the vascular pole, beside the afferent arteriole, and then breaks up into a second capillary network: peritubular capillaries around the cortical tubules (from cortical nephrons) or the long hairpin vasa recta that descend into the medulla (from juxtamedullary nephrons). This two-capillary arrangement in series is a portal system.
Efferent resistance is the key to the high glomerular capillary pressure (≈55–60 mmHg) and to the low pressure in the downstream peritubular capillaries that favours reabsorption. Angiotensin II constricts the efferent more than the afferent arteriole at low concentrations, raising glomerular pressure and filtration fraction to preserve GFR when renal perfusion falls.
- Location
Renal cortex, from glomerular vascular pole to peritubular capillaries or vasa recta.
Function
- Maintain glomerular capillary hydrostatic pressure
- Supply the peritubular capillaries and vasa recta (second capillary bed)
- Raise filtration fraction when constricted (angiotensin II)
- Regulation
Constricted by angiotensin II (AT1), sympathetic stimulation, endothelin; dilated by ANP and by ACE inhibitors/ARBs (removal of angiotensin II).
Clinical significance
ACE inhibitors and ARBs
By dilating the efferent arteriole they lower intraglomerular pressure — renoprotective in diabetic and proteinuric kidney disease (a small initial rise in creatinine, ≤30%, is expected) but dangerous in bilateral renal artery stenosis or volume depletion, where GFR depends on efferent tone.
Test yourself
Which feature distinguishes juxtamedullary nephrons from cortical nephrons?
- Their glomeruli lie in the outer cortex
- They lack a thick ascending limb
- They have long loops reaching the inner medulla and their efferent arterioles give rise to the vasa recta
- They make up about 85% of all nephrons
Answer: They have long loops reaching the inner medulla and their efferent arterioles give rise to the vasa recta
Juxtamedullary nephrons (≈15%) have glomeruli near the corticomedullary junction, long loops with thin ascending limbs extending to the papilla, and efferent arterioles forming the vasa recta — they create the medullary osmotic gradient.
Compiled from standard anatomy and physiology references — see the Urinary System sources. For education only; not medical advice.