Hi. It's Mr. Andersen and in
this podcast we're going to be talking about osmoregulation. Before we get into osmoregulation
we should define what osmosis is. Remember that is diffusion of water across a semi-permeable
membrane. So let's say right here we have this U-tube and on this side we have a high
molarity of water. So a lot of sugar on this side. On this side we don't have as much.
And so basically the sugar would love to spread out. But it can't because the sugar can't
fit through the semi-permeable membrane. But the water can. So the water is going to flow
from an area of high water concentration to low water concentration. And so basically
if you were to watch this, you couldn't see the sugar but the water on this side would
mysteriously raise. And lower on this side. It would require no energy. If you were to
do the opposite of that, so if you were to do reverse osmosis, we'd have to squeeze it
in this direction. We could get pure water and that's how you actually purify water if
you look on your water bottle. It'll say reverse osmosis a lot of the time. So how does this
impact cells? Because in plant cells it's okay for there to be movement of water because
they have a cell wall. But for us not so much. And so basically if you were to take a red
blood cell and have it sit in an isotonic environment. In other words an environment
where the concentration in the blood and outside the blood is the same, you're going to get
a movement of water but the blood cells are going to be happy like they're pictured right
here. \b
\b0 If you put them in a hypertonic area, so if you put them in sugary water then water
is going to flow out. And you can see that the red blood cells are going to shrivel up.
Likewise if you were to put them in distilled water, water is going to flow in and they're
going to pop. Or they're going to lyse. And so it's really important to the cells in our
body that they remain isotonic. So, what are the two life strategies? Well the two life
strategies are some organisms have just decided this is too much effort. And so what they
are called is osmoconformers. And so an osmoconformer like this octopus right here, the osmolarity,
and so osmolarity remember is going to be the concentration of solutes to water, is
going to be the same on the outside as it is on the inside. In other words they're just
going to be the same osmolarity as their surroundings. It's nice because they don't have to regulate
that. The bad thing is that you're going to get big swings that can effect the rest of
the organism. So a lot of organisms are what are called osmoregulators. Great example of
this would be the brine shrimp that are found in salt water. Brine shrimp, we would have
some like in the Great Salt Lake, basically what they do is they have to regulate the
amount of water inside them. So they live in a salt water environment. So think about
where the water is going to flow. Is it going to want to flow into them or out of them?
That's right. It's going to flow out of them. So they're going to, water is constantly going
to be lost. So they're going to have to do a lot of effort. In fact 30 percent of their
metabolism just goes to regulating this balance of osmolarity. If we think about fish, or
fish that live in a fresh water environment versus a salt water environment, if you really
understand osmosis, this is easy to think about. If you're a fish living in a fresh
water environment, where is the saltier area? It's going to be inside the fish. And so basically
they're going to keep having water flow into them. And so they don't drink water. That's
the blue here. Basically they eat food but they have urine that is really, really dilute.
And that's just because they're going to have a net influx of water due to osmosis. If you
move to a salt water fish, so in a salt water fish we're going to have the opposite problem
now. Now the salt water is going to have a higher solute concentration. So we're going
to have water that's going to keep flowing out of them. And so they have to actually
drink salt water. And their urine is going to be really really concentrated. Okay. So
we're not fish. We're not brine shrimp. We live on land. And so how do we osmoregulate?
Well we osmoregulate using this organ right here. It's called the kidney. And so this
is the kidney. It's going to empty urine into the bladder. And then we finally get rid of
that. But we use that on land to regulate our osmolarity. And living on land it's almost
more important that we're able to do that. Now this gets a little complex, but if you
can hold with me I think you'll understand how this works. So basically, let me go back
for just a second. If this is the kidney right here. On the inside of the kidney, over and
over and over again we're going to have this which is called the nephron. So the nephron
repeated over and over and over essentially makes a kidney. And so basically what happens
is blood is going to flow in. Blood is going to flow into something called the glomerulus.
And then it's going to flow into this which is called the Bowman's capsule. The Bowman's
capsule is going to do one thing. It's going to filter the blood. We also have proximal
and distal tubules. That's important for secretion and reabsorption. But we're not going to talk
about any of that right now. Again what we're focusing on is the water. Okay. So basically
what happens is the blood flows in and a lot of the water and solutes are going to squirt
out and they're going to move into this filtrate. This is eventually going to become urine.
So again this is eventually going to go over here and end up in your bladder. So basically
what's happening down here? Well as it enters into the renal medulla, basically what's going
to happen is water is going to flow out. And water is going to flow out. And as water starts
to flow out the osmolarity inside this descending tubule is going to increase. And so the concentration
at the beginning is around 300 milliosmoles. But it's going to increase to the point down
here where it's around 1200. So we're going to set up a gradient. And so on this side
water is going to flow out. Water is going to flow out. Water is going to flow out. Now
it's not just flowing out into the interstitial fluid. A lot of that water is being reclaimed
because we're going to have capillaries outside here as well. And so on this descending side
of the loop of Henle, that's what this is called, basically what's going to happen is
it's going to release water. And so we're going to set up a gradient. Now on the ascending
side, on the other side, we're . . . on the right side of it, it's not going to be permeable
to water. But it is going to be permeable to salt. And so basically what's going to
happen on this side is we're going to lose salt. And we're going to lose salt. And we're
going to lose salt. And as we get into this thick portion of the loop of Henle, we're
actually pumping that salt out. And so basically now what we have is a gradient where down
here it's 1200 milliosmoles. But then we have it going all the way back up. So it's 300
milliosmoles up here. And so basically it goes horizontal all the way across here. So
what's the work of all the loop of Henle for? All of the work is to set up this gradient.
And this is called a counter current exchange. So it's important that the fluid is following
an opposite direction. So these are interacting with each other. So basically we've set up
a gradient where on this side it's not as concentrated. As we move down here it's really
really concentrated at the bottom. So let me remove all of that. So again we're going
to have 300 up here. We're going to have 1200 down here. And so basically there's a gradient
that goes across like this. Okay. So what is this? This is called the collecting duct.
And so basically now we have control over that water. And so again this is the filtrate.
It's eventually going to become urine. But basically we can control whether or not we
let water out. And we do that using a hormone. And that hormone is called antidiuertic hormone.
Think about the name. It's anti-diuretic. Diuretic is anything that, just think about
diarrhea, it's releasing water. So an antidiuretic is something that has us hold on to water.
So basically we have this gradient right here. And if we release antidiuretic hormone which
is going to come from the posterior pituitary, it's going to interact on this collecting
duct over here. When it interacts with this collecting duct it basically says you can
let water through. And so if you can let water through, water is going to flow out of here
and it's going to flow back into our capillaries and into our interstitial fluid. And so basically
if we secrete a lot of ADH, basically this gradient is going to allow us to reclaim water.
And more water. And more water. And more water. And more water. And even though we've gotten
almost all of the water out of our urine, it's really concentrated out here. So osmosis
is going to pull that water out it. Likewise, let's say we drank a bunch of water and we
don't need to reclaim that. Then we're going to decrease the amount of ADH. And basically
now we can't let water out through here. And so that water instead is just going to flow
out into our urine. And so when you look at your urine and look at the different color
in it, what's responsible for that? Well basically it's the amount of ADH that we're releasing.
But more importantly it's this wonderful gradient that was set up in the loop of Henle. And
so that's osmolarity. Again we're osmoregulators. And you can thank our kidneys and our nephrons
for that. And I hope that's helpful.
