Hi. It's Mr. Andersen and in this video I am going to talk about interstitial
fluid. Interstitial fluid is a term that confuses students. If you ask them what is a capillary
they know that. They know what's in blood. They know what cells are and the tissues are
made up of cells. But if you ask them what interstitial fluid is, they're confused. And
that's too bad because that's going to be found between the capillary and the cells
and so what is it like or what does it look like? Well think about this. This doctor right
here is doing arthroscopic surgery on a shoulder. And so how does that work? You've maybe see
videos of that. Well they put a camera in. And then they're going to introduce fluid
in there, but basically what does it look like inside our body? Well if you take a camera
and put it inside our body, it's not just blood everywhere, the blood is going to be
confined to the blood vessels, but there's still going to be fluid inside our body. And
what is that fluid? That fluid is called interstitial fluid. And so really it's going to be what
separates all of our cells from the circulatory system. Since we have a closed circulatory
system that means that the blood is going to be maintained within these vessels the
whole way around the loops, but how does the material get out of the blood and eventually
get into our cells. It goes through the interstitial fluid. And so if you visualize it like this,
it's a fluid on the inside of our body that surrounds all the cells, then you're getting
there. And so there's microcirculation that takes place at the level of the capillary.
And so as the blood is flowing away from the heart, it will work it's way down eventually
to the capillary. And what holds the pressure inside a capillary, well there's going to
be hydrostatic pressure. Hydrostatic pressure is going to be the pressure out on the capillary.
It's pushing out. If you want to get an idea of what that really is, what is that hydrostatic
pressure? Well if you were young and you played with a hose when your having a water fight,
if you could ever get a hold of the hose, and you put your finger on the front of it,
you could increase that pressure and squirt it farther, and so that pressure on the inside
of the capillary out on that fluid is going to be hydrostatic pressure. And that's going
to move fluid outside of the capillary into the interstitial fluid around it. There's
also going to be osmotic pressure. What's osmotic pressure? That's going to be water
flowing in because we're going to have a higher solute concentration on the inside. So the
combination of these two pressures, hydrostatic and then osmotic pressure is going to create
that blood pressure on the inside of our vessels. Again, it's going to be probably greater hydrostatic
pressure on the capillary or the artery side and less on the venual side. Where does the
water go though? When it leaks out, what's going to happen to this water, or this fluid
as it moves out? Eventually it's going to move into what are called lymph vessels. And
those lymph vessels will return that fluid to the blood. And so the major parts of the
blood stay within the capillary but the fluid is going to move between the two. And so I
put together this little diagram to show you that. And so this is a capillary. So the capillary
is going to be, if I were to ask you what it's made up of, the capillary itself is going
to be made up of cells. And so the surrounding of the capillary or that tube of the capillary
is going to be made up of endothelial cells. So it's going to be these really thin cells.
What's on the inside then of our capillary? This is going to be plasma on the inside and
then we're going to have these red blood cells. We'd also have platelets in here and we're
going to have white blood cells as well. But if we're just talking about interstitial fluid
this plasma on the inside of our blood is very similar to the interstitial fluid. And
so what's going to be in the interstitial fluid. Well there's going to be a lot of water,
but we're also going to have sugar, salt, hormones, neurotransmitters, carbon dioxide,
oxygen. And so it serves as a conduit between the capillary and the tissues itself. And
so what's a gas that the cells are going to consume? They're going to consume oxygen.
How does it get there? Well it's going to be consumed here in the mitochondria but it's
going to diffuse from the red blood cells, through the plasma, through the interstitial
fluid and it's eventually going to move here. What's going to happen to the carbon dioxide?
It's going to build up inside the mitochondria. It's going to diffuse out. It's going to diffuse
through the interstitial fluid, it's going to diffuse through here and it's going to
be carried as bicarbonate on the red blood cells. And so really inside our body, what
do we have? We have cells and so red blood cells, the lining of the capillary are cells
and then clearly all the cells that make up our tissues, and then we're going to have
fluids. And really that's it. That's about the two things that we have. We're going to
have some things obviously that are matrix, made up from material that are produced by
cells. But the interstitial you can see is very important. That interstitial fluid because
it is going to be what surrounds our cells and it's going to be how nutrients get from
the blood into our cells and waste products get back. That's interstitial fluid. It's
clear. If you really want to know what it looks like, well think about the plasma inside
blood and that's essentially the same thing. And I hope that's helpful.