00:01
Now we're going to talk about
one of the most important muscles
in the entire body,
the diaphragm.
00:06
It's so important because
the diaphragm is the muscle
that primarily helps us breathe.
00:11
It's also what separates
the thorax from the abdomen.
00:15
In fact, phragm means fence.
00:18
So it's essentially the fence
that separates the thorax
from its next door neighbor,
the abdomen.
00:24
The diaphragm is kind
of a complicated shape,
and there's a lot going on,
so use yours
to take a deep breath,
and we'll dive right in.
00:33
The diaphragm occupies
and seals off essentially,
the inferior thoracic aperture.
00:40
Therefore, all of its
attachments are going to mirror
the borders of the
inferior thoracic aperture.
00:46
For example,
we'll have this xiphoid part
where it's joined to
the xiphoid process.
00:52
The costal part where it's
joined to ribs seven through 12.
00:57
And the lumbar part,
downward attaches to
the lumbar vertebra L1 to L3.
01:04
If we look from above,
if we have a superior view,
looking down on the diaphragm,
we see that this sort
of dome shaped muscle
has fibers that travel centrally.
01:16
And they meet up
at this large flat sheet,
sometimes called an aproneurosis,
but specifically here
called the central tendon.
01:24
And so as these fibers contract,
it will draw the
diaphragm inferiorly,
which will increase the
thoracic cavity volume,
which will lower the pressure,
and will subsequently
cause the lungs to expand.
01:39
And so that's how the
diaphragm helps us breathe.
01:44
Now, it's great that it fills the
entire inferior thoracic aperture.
01:49
But there are some structures
that still need to pass
between the thorax and the abdomen.
01:53
So we have some openings.
01:55
We see one right here in the central
tendon called the caval opening.
02:00
And it's called that because
that's where the inferior vena cava
is going to pass through
to reach the right atrium.
02:07
Just to the left and
posterior to that
we have another opening
and that's the esophageal hiatus,
where the esophagus is going to pass
through on its way to the stomach.
02:17
And then most posteriorly
we have this hole here,
which is the aortic hiatus.
02:22
Where the thoracic aorta
is going to pass through
and then on the other side
turn into the abdominal aorta.
02:29
Now let's look at those
openings from below.
02:32
So if we look from below,
from the abdomens point of view,
we again see the caval opening.
02:39
And for reference,
to give you an idea,
roughly of where we're at,
we're at about
the T8 vertebral level.
02:45
And as the name implies,
the inferior vena cava is
going to pass through there.
02:51
We're also going to
have some branches
of the right phrenic nerve
taking advantage of this opening.
02:56
Just to the left and posterior
is that other opening
about the T10 level.
That's the esophageal hiatus.
03:04
Where the esophagus is
going to pass through.
03:07
And we're also going to have
some trunks of the vagus nerve.
03:11
Then finally, most posteriorly
we have that aortic hiatus
all the way down at around
the T12 level,
where the aorta is going
to transition from being
a thoracic aorta
to an abdominal aorta.
03:24
And it's also where
the thoracic duct
is going to be passing from
the admin up into the thorax.
03:32
If we focus a little
bit more on the inferior
and posterior portions
of the diaphragm,
we see some weird stuff going on.
03:39
We have what are called crura.
Crura just means the legs.
03:42
And we have
a right leg or a right crus
and a left leg or a left crus.
03:48
On either side of the inferior
most portion of the diaphragm here.
03:54
And if we zoom in in that area,
and we look at the area
of the diaphragm,
especially around
the esophageal hiatus
where the esophagus
is coming through,
we see it kind of divides.
04:06
We see some of that dividing
into one leg off to the right,
the right crus,
and then the other off to the left,
which called the left crus.
04:15
There's this weird little thing
happening off of the right crus.
04:18
We see some of it
going over and around
and past the celiac trunk
of the abdominal aorta,
on its way to a portion of the
intestine called the duodenum.
04:30
And that's why this funny
little muscle is called
the suspensory muscle
of the duodenum.
04:35
Or you may have heard it by its
eponym the ligament of Treitz.
04:39
If you've had embryology,
you've probably heard of this
as an important landmark
for rotation of the gut.
04:44
But it's also an important
landmark in just anatomic sense
because this is what
we generally say
divides the GI tract
into upper and lower.
04:54
So for example, if you're saying
an upper GI bleed
versus a lower GI bleed,
this is to the point where we're
talking about upper becomes lower.
05:04
Alright, so let's talk about
the innervation a little bit.
05:07
So, we have the phrenic nerves,
and the phrenic nerves
originate up in the neck
and traveled down through
the mediastinum on their way
to the diaphragm to provide
motor innervation there,
but we also see as it's going
through the mediastinum.
05:23
it's giving off branches.
05:24
And we see for example, there's
some pericardial branches here.
05:29
And so there's going to be
a lot of sensory innervation
provided by the phrenic nerves
before they reach the diaphragm
to provide motor innervation.
05:39
And they're going to go all the way
to the undersurface or
the abdominal surface,
where they're going to terminate
as phrenicoabdominal branches
very appropriately named.
05:52
Sometimes there can even
be a little ganglion
called the phrenic ganglion
that will communicate with the
celiac ganglion down in the abdomen.