Hi. It's Mr. Andersen. Today I'm going to be talking about homeostasis hugs. One of
my favorite videos on YouTube is the Free Hugs video. I think it has something like
72 million views. This guy walks around with a free hugs sign. Takes him forever but he
finally gets his first hug. And so then it goes on to get all these hugs. They eventually
band hugs. But give it a watch. Here's the address right down here. But basically when
you're hugging somebody or when you're wrapping your arms around somebody you're transferring
something between the two of you. And in a hug that's called love. And so in this podcast
I'm going to talk about hugs. But not hugs between people. It's hugs between tissues.
And those tissue hugs are used to maintain homeostasis. Or to maintain an internal stable
body or environment. And so let me get rid of this and go to some actual homeostasis
hugs. And so the first one I want to talk about is something called countercurrent heat
exchange. And we actually use it in engineering to keep a house warm. But basically it keeps
an organism warm. And so we would see this like in the legs of a moose. We'd see it in
the feet of a bird or in the flippers of a dolphin. Countercurrent heat exchange works
like this. Basically if you think this is the body of the moose standing here on the
snow. You want to maintain that heat inside the body. And so basically this right here,
the leg of the moose I've drawn over here. So this is going to be the top of the moose.
This is going to be the hoof of the moose down here. And then this is going to be the
body of the moose up here. So basically we want to keep heat up here. So what they have
is they have the arteries. So the artery is moving blood away from the body. And the vein
is returning blood to the body. What they'll do is they[ll wrap those right around each
other. So they'll be hugging. And what they're transferring is not blood. What they're transferring
is heat. In other words we have a high temperature, we'll say right as it leave the body. Let's
say the temperature is close to 100 degrees, or is right next to blood that is cooler than
that. And so the heat is going to flow from a warmer to a cooler area. But what happens
is since it gets progressively cooler here, a lot of that heat actually moves back up
to the body before it goes way down to the extremities. And so you'll have in the hoof
of a moose, you're going to have a temperature that's pretty much near freezing. But it's
not cold enough that the tissues will die. But the nice thing about a countercurrent
heat exchange is this holding all that heat right up here inside the body. And you have
the same thing. And we can actually turn that on. We can hold that when we're starting to
get really, really cold, hold that body heat next to ourself. But it only works if the
artery and the vein are hugging each other. They're really really close. Next one would
be in the lungs. And so what's the homeostasis? What's it trying to maintain? It's trying
to maintain oxygen inside our body. And so there are alveoli which are these little sacs
inside the lungs. But it you look right here they're being hugged by capillaries. So the
capillaries are wrapped right around it. So again you should always be thinking if there's
a hug what's being transferred between the two? In this case it's oxygen is being transferred
from the alveoli into those capillaries. And carbon dioxide is being loaded off into the
alveoli. So it can eventually leave. And so it has to be a very close contact between
the two. In fact it's just one thin layer of cells between these two tissues. And that
allows us to transfer those gases and keep us maintaining that homeostatic environment.
In other words the right amount of oxygen inside each of our cells. Next one would be
a little bit more confusing. Again we're going harder. This would be the nephron. So the
nephron is going to be inside the kidney. What a kidney does is essentially four fold.
Number one is it's going to do filtration. So it's going to filter. So let's go filter.
Next it's going to secrete. Next it's going to reabsorb. And finally it's going to excrete.
Those are the four things that a kidney essentially does. Okay. So how does that work? Well basically
the blood, if we follow this cursor here, the blood is flowing up. It's flowing up through
these capillaries. And eventually smack it ends into the end of the glomerulus. Right
here is the end of that pathway. And if you look here, where's the red coming out? The
red doesn't come out. The red goes in and out the same exact same way. And so that's
how we get filtration of the blood. The little things will squirt out here into the filtrate.
Next though we want to secrete things that we don't want to have inside our body. And
then reabsorb some of the things that we actually do. So small things that will filter out right
here. But as it moves through this proximal and then eventually through this distal tubule,
there are large things that we want to use active transport to actually reabsorb and
move out. And so also as we go through the loop of henle water is one of those big things.
That we have to move water out and sodium out. And so if you look there's hugs this
whole way through the proximal and distal tubule. So what are we transferring? Right
here were transferring things, large things that we want to get rid of. Or large things
that we want to keep. And it doesn't work unless we have this close contact between
those tissues. So again, another hug. The last one I want to talk about is countercurrent
gas exchange. And this is going to be found in the gills of a fish. And so if you live
in water you face a major issue. And that is that there's not much oxygen available,
O2 available inside the water. So you have to have a really efficient system for exchanging
oxygen with the water. Now it's moist. So that's something that we deal with on land.
But as that water comes in, you want to get as much of the oxygen in as you possible can.
And so the way it works in a fish is they have the operculum. So what they'll do is
they'll open their mouth. And as they open their mouth and they open this gill covering,
that's going to move the water right over their gill filaments. We call those lamella.
And the lamella are increasing surface area. So they're really, really small. But they're
basically set up so the blood is going to flow in this direction and the water is going
to flow in the opposite direction. So what does that mean? These capillaries in the lamella,
it's actually going to move the blood, so the blood will come through in this direction.
But it's going to be moving in opposition to the water which is moving in the other
direction. And the stat that I remember hearing is that they can get about 80 percent of the
oxygen that's available in the water, they can get that out. So what does that mean?
Right here as the water is flowing in, it's going to have 100 percent of the oxygen that's
dissolved inside the water. And when it leaves it's only going to have 20 percent. So you
might think, how did they get all of that out? Well they're using a countercurrent exchange.
In this case it's gas exchange. And so if we look at, what did I say, what's the number?
Well 80 percent is how much they're actually taking out. And so if we say right here we'll
say it's like 5 percent oxygen that maybe makes it around the body of the fish and comes
here. Well you can see here, that right here there's going to be exchange of gas from the
water, oxygen which is 20 percent oxygen, 5 percent right here. And so let's make up
the numbers here. Let's say this is 50 percent here. And down here it's going to be we'll
say 30 percent. And so right here there's going to be more oxygen available and so there's
more oxygen in the blood but it's meeting water that is even more pure. And as we get
up her to it's 80 percent water and this is like 60 percent in the blood, there's constantly
this gradient. And so as you get way to the end where we've taken out 60 percent of the
oxygen that we could get, you're facing water that is 100 percent pure. Has almost all the
oxygen that it possibly can. And so by putting the flow in this direction and the blood moving
in the other direction, we have this gradient. And it allows us to get the maximum amount.
And when I say we, the fish to get the maximum amount of oxygen they can out of the water.
And so that's another hug. And so it's going to be a close contact between the water in
this case and the capillaries in the lamella. And so that hug allows us to maintain homeostasis.
And I hope that's helpful.