Urinary System: Juxtaglomerular complex

Some background information:

Part of this distal convoluted tubule is opposed to the glomerulus. This region is densely nucleated, and is known as the macula densa. Here the epithelial cells are narrower, and the nuclei lie close together.

The afferent arteriole in this region contains specialised secretory cells (smooth muscle cells) called juxtaglomerular cells, that secrete renin.

These cells do two things:

1. They monitor blood pressure, by measuring how much the arteriole wall is stretched.
2. They monitor the concentration of sodium and chloride ions in the filtrate of the macula densa.

These two inputs tell these cells how much renin to release, to maintain blood pressure within normal limits, and keep the glomerular filtration rate constant.

For example, a decrease in blood pressure, causes release of renin, which acts on Angiotensinogen (from liver) resulting in conversion of Angiotensin I to Angiotensin II, which increases smooth muscle tone in arterioles, and thus increases blood pressure.

In between the epithelial cells of the macula densa regionof the tubule and the juxtaglomerular cells, are some paler staining cells called lacis cells.

Together all three types of cell make up the juxtaglomerular complex.