Juxtaglomerular Apparatus

00:01 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.

00:28 They're called macula densa cells because they're concentrated together, the nuclei look very close together.

00:36 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.

01:01 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.

01:35 And renin, therefore being a hormone, passes into the vascular system and initiates what we term the renin-angiotensin-aldosterone complex 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.

02:13 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.