You're watching a really, really long movie.

And you've finished your entire bucket of popcorn.

You've guzzled down a giant soda

and all of a sudden, you have to pee.

And to make matters worse, you're watching a movie

about a whole bunch of people on a cruise ship

that hit an iceberg and so, there's a lot of water

in this movie and you freak out because

now you have to get up and go to the bathroom.

But then that should get you thinking,

well, how do my kidneys work?

How is it that I can make all this pee

that I have got to get rid of?

Well in the next few videos, we're gonna

talk about how the kidneys work.

And I'll give a quick overview here

before we delve more into the specifics.

As you can see, the kidneys sit

right here around your belly button.

They're about the size of a fist and you've got two of them.

And they sit a little closer

to the back, not really in the front.

So the kidneys receive blood from the heart.

So the heart goes on up here.

It's also about the size of a fist.

And it pumps blood throughout the body.

You know, you get some to your arms,

you have some that goes up to your brain,

and you have this branch that comes down

and it goes towards your legs, as well.

Well, what you can kind of see

in the picture of the kidneys right here,

is that they've got a little vessel right there

so sure enough, there's some blood that comes

from the heart into the kidneys.

Both of your kidneys, then, are going to

filter the blood and release urine,

which is just a collection of waste products

that your body wants to get rid of.

And the urine is gonna hang out

in your bladder that sits about right here,

until it's an appropriate time to go to the bathroom.

And that's kind of a broad overview.

But let's go into a little more detail

about what the kidneys do.

So I'm going to draw a box over here.

And this box is going to be what the kidneys do.

So I'm going to give just a really simplistic

overview of what the kidneys do.

And then in other videos, we'll go dive deeper into detail.

So as I mentioned, each of your kidneys

gets an oxygenated blood vessel,

or an artery that goes to them.

And your arteries hold onto all the things in your blood.

This can include things like your nutrients.

And so nutrients can be anything from say,

your electrolytes like your sodium ions.

They can be things like your proteins or your

amino acids or even glucose, as well,

things that build your carbohydrates.

So a lot of things that your body uses

as the building blocks, or things that help

other structures of your body work.

In addition to your nutrients, you've also got

oxygen hanging out in your arterial blood.

And your arteries also contain waste products.

So things your body has made through cellular respiration

and all these other processes that we undergo

that we don't need anymore, that we want to get rid of.

And they can include things like urea and other

toxic compounds that we don't want to build up.

And at the same time, it can also include

extra electrolytes, like sodium that we don't need.

Because if we hold onto a lot of sodium chloride,

which is just salt, we'll end up having high blood pressure.

So our kidneys also help us maintain our

blood pressure, as we'll talk about in other videos.

So, this just kind of underlines

the point that if you have too much

of your nutrients, they become waste products.

And so, your kidneys help to make sure you don't

build too much of this good stuff here.

So this is all the stuff you've got hanging out

in the artery that's coming over to your kidney, right here.

And as you might recall, whenever you have

an artery coming into an organ or a part of your body,

there should be a vein that takes the blood away

from it that's going to return it to the heart.

So this is your vein, right here.

And so the job of the kidneys then, is to make it so that

the nutrients you had in your arterial blood

are collected and maintained when we get to the vein.

So we want to hold on to our nutrients, right here.

So I'll just write "nutrients".

And it stands for all the stuff that I

gave examples for on the left side here.

And the kidneys, like every organ

in the body, need oxygen to do well.

So you'll have the oxygen go through the kidneys

and some of it will make it out.

Some of it will be used by the kidneys.

Because that's how we can maintain some of the tissue.

And so when we get to the other side,

where the vein is, we'll have less oxygen.

So I'll write it really tiny right here to show

that there's much less oxygen in your venous blood

than there was in your arterial blood.

And finally, the kidneys want to take all the

waste products your arterial blood brought

to the kidney and hold on to it, make it so that

this stuff does not end up in the venous outflow.

And by collecting these waste products,

the kidneys will effectively produce your urine.

Now, you might notice in this picture

that I am missing something.

What connects the artery to the vein?

Well actually what goes on here

is part of what makes the kidney so special.

And it answers the "how".

How is it that the kidneys are able to do this?

How is it that the kidneys can help us

maintain our nutrients in our body

while getting rid of waste into urine?

Well, the kidney is special

because it's got two capillary beds.

I think you might have heard

what a capillary is before, alright?

A capillary bed is just something that

connects the artery and the vein.

It's where you can have oxygen flow out.

You can have nutrients flow in.

So the way I'll draw it is that you've got one

capillary bed, right here, connecting your

artery to your vein, like that.

And you've got another one down here connecting those two.

And so these guys work together to deliver oxygen

to the kidney's tissue and, at the same time,

recollect these nutrients so that the vein can

take these nutrients elsewhere in the body for use.

And these capillary beds have two fancy names.

The first one is called the vasa recta.

The vasa recta.

And that's mainly to give oxygen to the kidneys.

The other set of capillaries are

called peritubular capillaries.

Peritubular capillaries, and we'll talk way more

into detail about these peritubular capillaries.

And these are the guys that are mainly

going to be responsible for collecting

nutrients that our kidneys will filter.

And we'll talk more about that

process in the next few videos.