Juxtaglomerular apparatus
Complexus juxtaglomerularis
Also known as: JGA, juxtaglomerular complex
A sensory–secretory complex at the vascular pole of each glomerulus, formed by the macula densa of the distal tubule, renin-secreting juxtaglomerular cells of the afferent arteriole and extraglomerular mesangial cells; it regulates GFR (tubuloglomerular feedback) and renin release.
Overview
Each nephron's thick ascending limb returns to its own renal corpuscle and touches the angle between the afferent and efferent arterioles. Here three cell populations form the JGA:
Macula densa — a plaque of tall, closely packed tubular cells at the end of the TAL that senses luminal NaCl via NKCC2. Juxtaglomerular (granular) cells — modified smooth muscle cells in the wall of the afferent arteriole that store and secrete renin and act as intrarenal baroreceptors. Extraglomerular mesangial (lacis/Goormaghtigh) cells — located between the arterioles and the macula densa, coupled to the others by gap junctions.
The JGA links tubular and vascular function. Tubuloglomerular feedback: when GFR rises, more NaCl reaches the macula densa, which releases ATP/adenosine → A1-receptor-mediated afferent arteriolar constriction → GFR returns toward normal. Renin release increases with (1) low perfusion pressure sensed by JG cells, (2) low NaCl delivery to the macula densa (signalled by PGE₂ and NO), and (3) sympathetic stimulation via β1-adrenoceptors.
- Location
Vascular pole of each renal corpuscle, renal cortex.
Parts & subdivisions
- Distal tubular NaCl sensor.
- Renin-secreting cells of the afferent arteriole.
- Lacis cells relaying signals.
Function
- Tubuloglomerular feedback — autoregulation of single-nephron GFR
- Secretion of renin — initiation of the RAAS
- Integration of pressure, NaCl and sympathetic signals in blood-pressure control
- Regulation
Renin release ↑ by hypotension/hypovolaemia, low macula densa NaCl, β1-sympathetic stimulation, loop diuretics (block macula densa NKCC2); ↓ by angiotensin II (negative feedback), ANP, high NaCl intake, β-blockers.
Clinical significance
Renovascular hypertension
Reduced perfusion of the JGA (renal artery stenosis) drives inappropriate renin secretion and angiotensin-II-mediated hypertension.
Juxtaglomerular cell tumour (reninoma)
Rare renin-secreting tumour of young adults causing severe hypertension and hypokalaemia with very high renin and aldosterone.
β-blockers lower renin
Part of the antihypertensive action of β-blockers is suppression of β1-mediated renin release from JG cells.
Compiled from standard anatomy and physiology references — see the Urinary System sources. For education only; not medical advice.