Renin production in the kidneys Learn the three major triggers for Renin production by the Juxtaglomerular cells. Rishi is a pediatric infectious disease physician and works at Khan Academy.
Renin production in the kidneys
- We talked about how there's an efferent and an afferent arteriole.
- This is the afferent arteriole, going towards the glomerulus, there's a whole clump of blood vessels here.
- There's the efferent arteriole which leaves that clump of blood vessels.
- Those blood vessels we know are gonna be surrounded by Bowman's capsule.
- We named all the different parts of the nephron.
- The proximal convoluted tubule, the loop of Henle,
- and this is the distal convoluted tubule. I'm drawing it in between the afferent and efferent arteriole on purpose.
- This is where all the different distal convoluted tubules meet up into that collecting duct.
- In this section, in this little video, I want to expand on this little piece.
- Where the efferent and afferent arteriole are coming together into that glomerulus
- between that there's that distal convoluted tubule.
- Just keep that picture in mind as I start expanding this drawing.
- Over here we have the afferent arteriole, I'm gonna start drawing it, I have enough space here.
- Something like that.
- These are the endothelial cells that are lining that blood vessel, that arteriole.
- On this side we have the same endothelial cells of course, but now it's leaving the glomerulus.
- We've got coming and going, over here is the efferent arteriole.
- The other one is of course the afferent arteriole.
- I'm gonna reverse that arrow, just so there's no confusion about the direction of the blood flow.
- I don't want you to be confused about where the blood is going.
- It's gonna be going like that and this is the afferent arteriole.
- I've got my blood vessels labeled.
- Between the two I also have the distal convoluted tubule, so let's draw that in.
- This are the cells surrounding the distal convoluted tubule.
- There are some very special cells in here, I'm gonna draw them in a different color.
- They are the macula densa cells.
- They're part of the tubule, but they're very special, so I'm gonna draw them for that reason.
- This is the distal convoluted tubule.
- And in green are the macula densa cells.
- I'm throwing a lot of names at you and I want you to start feeling comfortable with these names,
- because they're gonna be used quite a bit.
- It's not particularly hard once you get used to the language, but I know it can be confusing to see all these funny words thrown at you.
- The next thing I want you to think back about and remember is that arterioles don't just have one layer.
- We know that arterioles have multiple layers.
- The inner layer, the tunica intima, is the endothelial cells, we know that.
- There's also smooth muscle cells. We know that there's also a layer called the tunica media.
- That's here, with smooth muscle cells.
- I'm gonna try to draw some smooth muscle cells right there.
- We have a layer of these smooth muscle cells.
- If you look closely under a microscope, you'll see that there are also some interesting cells right here.
- I'm drawing them in blue, just to highlight that they're different.
- They are actually very similar to smooth muscle cells.
- In a way they're specialized smooth muscle cells.
- Let me label these two cell types that I've drawn for you.
- Smooth muscle cells, they're on the afferent arteriole side.
- You'll see them a little bit on the efferent arteriole side as well, but mostly on the afferent arteriole side.
- Smooth muscle cells. Then you have these juxtaglomerular cells.
- Juxta, talk about a funny word...
- Juxtaglomerular cells.
- All right, so the juxtaglomerular cells are there.
- If you looked under a microscope, they'd be full of granules.
- Sometimes they're even called granular cells.
- Let me draw in some granules just to remind you that's what people see under a microscope.
- Little green granules in this case.
- I'll put them into all of them.
- You know that these cells are on both sides of the vessel, because of course we cut it longways,
- so we're just looking as if it's disconnected.
- But these two sides are obviously touching, if you thought of it in three dimensions.
- Now I've talked about four cell types, let's round it up with a last cell type.
- This is in orange now, these are the mesangial cells.
- Mesangial cells are there for structure.
- They're really there to hold the whole thing together so that the blood vessels and the nephron are in close contact.
- So that they're structurally sound. Think of them as being there for support reasons.
- These are the mesangial cells.
- Combined, if you think about all this stuff together, remember this is all the white box in the little picture blown up.
- If you think about all this stuff together, the macula densa cells, the endothelial cells, the smooth muscle cells,
- the juxtaglomerular cells and the mesangial cells, put together, this whole thing is the juxtaglomerular complex.
- Or apparatus rather, the juxtaglomerular apparatus.
- Kind of a funny word, but it's how people refer to all these cells, the juxtaglomerular apparatus.
- The key here is to remember that the goal of the juxtaglomerular apparatus is to release renin.
- Think about where renin is. I mentioned these little granules here.
- These are actually each gonna be loaded with renin.
- These little granules dump themselves into the vessels, this is your renin.
- That renin is gonna make its way into the afferent arteriole, just like I drew it,
- then it's gonna make its way through the glomerulus.
- On the other and it's gonna sprinkle out and go into the efferent arteriole.
- That's the way renin gets released.
- What we hadn't figured out yet, what we hadn't said, is how, why would the juxtaglomerular apparatus release renin.
- What is the trigger?
- Let's figure out what are the key triggers for the release of renin.
- What are the triggers?
- There are three actually. Three common ones we know.
- One is simply low blood pressure. This cells are gonna feel mechanically less blood pressure.
- They're gonna say 'What's going on here? Pressure is low, we've got to do something about it.'
- 'We're gonna release renin.'
- So one trigger would be low blood pressure.
- That's the first one and it's actually directly sensed by the juxtaglomerular cells.
- That's actually sensed right here. I'm gonna draw a 1 for that.
- The second trigger is a nerve cell trigger.
- Actually I haven't even drawn that in for you yet.
- Remember that this is a blood vessel, right here, with our two layers, our endothelial layer and our tunica media layer.
- There's also an external layer, the tunica externa.
- We also have a blood vessel here, these mesangial cells, they're also specialized smooth muscle cells.
- We have these layers of blood vessels and the two blood vessels are kind of merging and fusing right here.
- They're coming together right here.
- In this external layers you actually have, I'm gonna draw it in yellow, you have these little nerve endings.
- Remember that nerves can end in that layer, the external layer.
- You have the sympathetic nerve endings.
- They come and sit with their nerve endings right on the juxtaglomerular cells.
- They're sitting right there and when they fire, that's gonna make the JG cells want to dump their renin.
- So the second trigger is sympathetic nerves.
- Now there's one more trigger, the third trigger.
- This one is actually a little distance away.
- It's the macula densa cells.
- I mentioned them earlier and I said that they're special.
- I haven't really gotten into why they're special. Let me tell you what happens.
- What happens is these macula densa cells, they're sitting there in the distal convoluted tubule,
- sampling what comes through. They're just kind of feeling what comes through.
- They're seeing sodium come through.
- They're checking and checking, is there a lot of sodium coming through, or a little bit of sodium.
- When they start sensing that the sodium content, that the amount of sodium
- coming through that distal convoluted tubule is really quite low,
- when they start feeling like not too much sodium is coming through,
- they start thinking to themselves 'Why is this happening?'
- If you think about it, you can figure it out too.
- If there is not a lot of sodium here, that's probably because there's not a lot of sodium here.
- And that could be because there's not enough sodium here or here.
- So really, when the distal convoluted tubule senses low sodium,
- it's probably related to the fact that not enough sodium is getting in at the getgo, at the point of filtration.
- And that could be a reflection of low blood pressure.
- So when the macula densa cells sense low sodium levels, what they're sensing is low pressure in the glomerulus.
- So if there's low pressure in the glomerulus, our glomerulus right here,
- they think 'Ok,that's probably the reason our sodium levels are low.'
- 'Let's send a signal out to the juxtaglomerular cells.'
- Low sodium in the macula densa, picked up by the macula densa rather.
- It means that the filtration pressure in the glomerulus was too low.
- So what they decide to do, let me find a new color, maybe something like this.
- They send a little messenger.
- I'll do my messenger in orange.
- They send a messenger to go over to the juxtaglomerular cells.
- That messenger is a little molecule called prostaglandin.
- It's a local messenger.
- It really doesn't act far away from these cells, it just acts locally.
- This local hormone, it's sometimes called a paracrine hormone, I'll write that here, paracrine hormone,
- is going to send a signal from the macula densa cells over to the juxtaglomerular cells.
- They say 'Hey, there's a trigger, we sensed low sodium and we think it's because of low blood pressure.'
- 'Why don't you go and do something about it?'
- So those are the three triggers.
- Actually I don't think I've labeled them well.
- This is trigger number two and this is trigger number three.
- These are the three triggers that will make the renin get released into our blood stream.
- This is a picture of renin, this is a picture of the molecule.
- I've actually already drawn kind of like a pacman-like shape around it.
- When I talk about renin coming out of the juxtaglomerular cells, you get a sense of what it actually looks like.
- This is a three dimensional figure of this protein.
- Keep in mind this is a protein hormone.
- Meaning it's a protein that has the ability of letting one cell talk to other cells at a distance.
- This is what that renin looks like.
- We'll discuss more about how renin works in the next video.
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