Osmosis and Osmolarity

by Jason Amores Sumpter
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before we get into the nitty gritty of how the kidney works, I want to review some concepts surrounding osmosis and diffusion. So to start, let's go over a little terminology. A salute is a substance that's dissolved in a solution, and an electrolyte is a specific type of salute that, when it dissolves, will actually disassociate in tow ions. So, for example, we have salt here. This is just like table salt, and it will dissociate into a sodium ion and chloride ion in water. Now, when salutes dissolve in water, if they don't spread out evenly, they will form a concentration Grady in, which is basically a difference in concentration of a salute over some areas. So here you can see we have a high concentration on this side and a low concentration on this side. There's blue dots representing the solids. This means that we have a concentration Grady int across this area. Now what's gonna happen if we have a concentration radiant and nothing is blocking. The movement of these salutes is we're gonna have diffusion, which is the movement of molecules, or atoms from an area of high concentration to an area of low concentration and you can see that happening here. This is diffusion, and you can see we have a high concentration here. But the's salutes are going to diffuse and spread out evenly throughout this solution. No, if we have something blocking those salutes from moving, there won't be any diffusion of solids. As you can see here we have a U shaped tube and there is a higher concentration of salutes on, uh, this particular side and a lower concentration of salt. It's on this side, but there's a membrane separating the two sides of the tube so those salutes won't be able to pass through on either side, so they can't defuse to spread out evenly. But what's gonna happen is we're gonna have movement of water across that membrane or osmosis, and the water is going to move from the area of low solute concentration to the area of high solute concentration. And the result is going to be that the water will balance the solute concentrations on each side. So here we actually have a higher volume on this side now. But as you can see, the concentrations of the two sides here and here is the same and that is due to osmosis. And, uh, that membrane is displaying selective permeability. Right? That is that the ability of salutes to cross or the prevention of solids from crossing due to the presence or absence of transport proteins. So here there's no transport proteins on this membrane, this membrane here for those salutes, so they are not going to be able to cross its impermeable to them. Now there are terms to describe the concentrations of salutes of two solutions. We use the term Osma Larry T to talk about the concentration of a salute, and it's a measurement of moles of dissolved solute per leader. You don't really need to worry about units for this. I mean, this is biology, you know, We just want to kind of think about it in terms of, you know, qualitative terms like, uh, you know, something having ah, higher Osma clarity than something else. And there's actually specific terms to describe that. So if a solution has a higher Osma clarity than another solution, we say that it's hyper osmotic. So if the solution that this cell here is sitting in is hyper osmotic, just gonna write hyper water is going to leave the cell because this area outside the cell has a higher Osma Larry t meaning that water is going to want to move out of the cell into that area of higher solute concentration in order to try to balance the solute concentration between the two environments. And it's going to cause the selfish shrivel. So again, the term for that type of solution is hyper osmotic. Here we have an example of iso osmotic solution where the solution outside the cell and the site is all inside the cell are of the same Osma clarity. So the water is going to flow in and out, um, at the same rate, So there's gonna be no net change in the amount of liquid in the cell. Lastly, the hypo osmotic situation which you can see here, is going to be when thesis allude concentration in outside or Sorry, the Osma Larry T is lower outside, uh, the cell than inside the cell. And so water is going thio enter the cell to try Thio Balance those solid concentrations. So again ah, you know hyper is higher Asthma clarity Hypo is lower Osma clarity and eso is sama's similarity. Now there are kind of like to Osma regulatory strategies that you'll see organisms have their osmo conformers, which tend to be marine organisms that are mostly ISO osmotic with their environment. So these guys aren't going toe actively regulate their, uh, their internal Osma clarity. Instead, they're just going to let it be iso osmotic with their environment. And that's okay because these marine organisms, you know, they live in salty water that has a very high salt concentration. Um, and, uh, you know is high enough that it's similar to the concentration inside cells, which is fairly high, actually. Now Osma regulators take a more active approach. These air guys who are going to actively regulate their asthma later the similarity of their internal environment. Last thing. I want to mention one really kind of weird strategy that some organisms show called an hydro bios issue, which is a type of crypto bio sis. It's, uh, basically an adaptation that allows organisms to survive, like without any water. These organisms will basically dry out or desa Kate and can still survive for quite some time like that. And example of that is this little guy right here that's technical name is a tartar grade, though I like the common name for it, which is a water bear. And this water bear is all nice and happy and plump with water. But these guys contrive out and shrivel into basically like nothing and still live like that for quite some time. So pretty wild adaptation. Lots of organisms have developed different strategies to deal with water balance. So with that, let's flip the page.