I want to now go back to what I was talking
about earlier when I mentioned
the macula densa cells and the juxtaglomerular
apparatus. On the left-hand side
of the diagram, the macula densa cells are a
group of cells right up close to the
efferent arteriole. They're part of the distal
convoluted tubule, and they're shown in
yellow at the top of the diagram.
They're called macula densa cells because
they're concentrated together, the nuclei
look very close together.
Dense spot is what macula densa means.
And they're actually in very intimate
contact with mesangial cells outside the
glomerulus called the extraglomerular
mesangial cells, but also they're in direct
contact with cells or smooth muscle cells
of the afferent arteriole. And those smooth
muscle cells get a special name.
They're called juxtaglomerular cells. And
there are gap junctions joining all these
cell components together. And the distal
tubule detects sodium chloride
concentration and blood pressure. When
sodium chloride concentration is very
low in the distal convoluted tubule or
if blood pressure is low,
those macula densa cells stimulate the
juxtaglomerular cells to secrete renin.
And renin, therefore being a hormone,
passes into the vascular
system and initiates what we term the
or system that again, you'll learn in your
physiology. So this is a very important
component of the kidney, controlling
blood pressure and also some degree
oxygen levels and content of the blood
itself. It's a monitoring unit.
These juxtaglomerular cells are often
difficult to see because often, you don't
see sections where you see both the
relationship of the distal convoluted
tubule to the afferent arteriole.