GLOSSARY

The macula densa is a group of tightly packed, tall epithelial cells in the wall of the end of the thick ascending limb and the start of the distal convoluted tubule, next to the vascular pole of the glomerulus. Its name means “dense spot”, because the nuclei of these cells appear close together.

Sensing Mechanism

The macula densa senses the sodium chloride concentration of tubular fluid through the NKCC2 transporter on its surface:

• High sodium chloride: release of ATP and adenosine → afferent arteriole constriction → lower GFR and inhibition of renin.
• Low sodium chloride: release of prostaglandin E2 and nitric oxide → afferent arteriole dilation and more renin release.

Importance

This mechanism, called tubuloglomerular feedback