Macula densa
Macula densa
A plaque of tall, densely packed epithelial cells in the wall of the terminal thick ascending limb, facing the vascular pole, that senses tubular NaCl and signals to the afferent arteriole and JG cells.
Overview
Macula densa cells are narrower and taller than neighbouring TAL cells, so their nuclei appear crowded together (hence "dense spot"). Their apical NKCC2 transporters sample NaCl in the tubular fluid. High NaCl delivery (reflecting high GFR) → increased NaCl uptake → release of ATP, metabolised to adenosine, which constricts the afferent arteriole through A1 receptors (tubuloglomerular feedback) and inhibits renin. Low NaCl delivery → COX-2-derived PGE₂ and nNOS-derived NO → afferent dilatation and renin release from JG cells.
Because loop diuretics block NKCC2 here too, the macula densa "sees" low NaCl and renin rises.
- Location
End of the thick ascending limb, at the vascular pole of its own glomerulus.
Anatomy
- Histology
Tall columnar cells with crowded nuclei and a polarised basal aspect facing the lacis cells and JG cells.
Function
- Sense distal tubular NaCl concentration
- Mediate tubuloglomerular feedback
- Regulate renin release
Clinical significance
SGLT2 inhibitors and TGF
By reducing proximal Na⁺ reabsorption, SGLT2 inhibitors increase NaCl delivery to the macula densa, restoring tubuloglomerular feedback, constricting the afferent arteriole and reducing glomerular hyperfiltration — one explanation for their renoprotective effect.
Test yourself
The macula densa regulates afferent arteriolar tone (tubuloglomerular feedback) by sensing:
- Afferent arteriolar wall stretch
- NaCl concentration of tubular fluid at the end of the thick ascending limb
- Plasma osmolality
- Plasma K⁺ concentration
Answer: NaCl concentration of tubular fluid at the end of the thick ascending limb
Macula densa cells take up NaCl via NKCC2. High NaCl delivery (high GFR) → ATP/adenosine release → A1-receptor-mediated afferent constriction → GFR falls; low NaCl → afferent dilation and renin release.
Compiled from standard anatomy and physiology references — see the Urinary System sources. For education only; not medical advice.