When you think about it, your body’s just a squishy meat sack.
You might have some muscles and bones that let you move around, but otherwise, all of
human life can be reduced to fluid filled bundles of cells.
And some of those bundles do useful things, and make for really fun dissections, but otherwise
there’s a bunch of empty space.
Our bodies take advantage of those empty spaces, or body cavities by filling them with important
squishy organs.
So today, we’re going to learn about body cavities, the organs that fill them, and the
membranes that wrap them up and protect them.
[intro]
What’s up everybody I’m Patrick Kelly back with a new semester of videos and I’m so
excited to have you with us.
Today we're talking about body cavities because I want to teach the container
before we teach what fills them
The human body isn’t /just/ a meat sack, it’s an /organized/ meat sack.
And learning about these cavities can help us understand what’s sitting next to what
during healthy conditions, or maybe what’s impeding something else during pathological
conditions.
You have a few different empty pockets throughout your body.
I’d break them up into either sinuses or cavities.
Usually these sinuses are empty, no organs, just mucus, fluid, or air.
Those sinus can fill up though, like you’ve felt if you’ve gotten a sinus headache or
sprained your ankle and experienced swelling in the sinus tarsi.
But we care more about body /cavities/ because of what they contain.
So I want you to first picture a lateral view, looking at someone from the side.
That’s where you’ll find our first two cavities, the dorsal cavity in the back and
the ventral cavity towards the front.
The dorsal cavity is fairly straightforward, it holds the two important pieces of the central
nervous system: the brain in the cranial cavity of the skull and the spinal cord in the vertebral
cavity within the vertebral column of the spine.
Now if our brain and spinal cord only had these hard bony shells for protection, they’d
be very uncomfortable.
Kind of like how bike helmets have a hard outer shell, but they also have extra soft
padding on the inside.
So these structures are wrapped in three layers of meninges and some liquid cerebrospinal
fluid for extra protection.
That’s a great feature for the dorsal cavity to have — these are really delicate structures
and you want to keep them extra protected.
On the flip side, the /ventral/ cavity has very few bony structures and /lots/ of padding.
This is where you’ll find your lungs, liver, intestines and reproductive organs among others.
And this less rigid, more malleable structure is a /great/ feature to have for these particular
organs.
Like your lungs change size and shape every few seconds, your spleen gets bigger if you
get sick, and you know, a baby can start growing in a uterus from time to time.
But some organs need a bit more protection and separation, so we organize again.
We can divide the ventral cavity further into two smaller cavities: the thoracic cavity
and abdominopelvic cavity which are separated by the big muscley diaphragm.
When we zoom into the thoracic, we’ll see two big organs and two more cavities — the
pericardial cavity which holds the heart.
Not a huge surprise considering it has the word cardial in it.
We also have the pleural cavity which holds our two lungs.
Coincidentally that’s how I remember them, because we don’t have singular lung we have
pleural lungs.
Inferior to the diaphragm we have the abdominopelvic cavity where we’ll find all the fun stuff:
most of the digestive system and some key players in the immune system.
What beginner anatomy students forget though is that this cavity extends all the way down
into the pelvis.
They know abdomen is somewhere from rib cage to waistline, but by including the pelvis
in this body cavity, we’re talking about contents that go all the way to your pelvic
floor muscles.
Finally, there are technically a few other body cavities like your orbital cavities that
house your eyes or your oral cavity with your tongue and chompers in it.
Otherwise that’s it.
Those are the traditional body cavities.
And with everything that we need to shove into those spaces, it can get pretty packed
and it would really pay off to minimize friction and organs rubbing on organs.
It’s like a really terrible nightclub.
Dark, cramped, sticky and you’re not sure what liquid just touched your leg but you
don’t like it.
This is where serous membranes come in, layers of epithelial tissue wrapped around major
organs that gives the organs some kind of lubrication.
So each of these serous membranes will have a few different layers which contain a very
small amount of serous fluid, a fluid with similar consistency to blood /serum/ which
is where this fluid and these membranes get their name from.
You’ll have a few different layers — starting with an empty cavity, say the abdominopelvic
cavity, you’ll want to line that cavity with parietal membrane.
Parietal comes from the word for /wall/, which I remember because you’d want to decorate
the walls before a parti.
Look, it’s a stretch, but it works.
Under that you’ll find some connective tissue and serous fluid, then another membrane called
the visceral membrane which wraps individual organs.
Since this membrane wraps individual organs, I think of someone asking you “hey, which
ceral is it?”
“/Visc/ceral!”
These are the memory devices you’re subscribed for, right?
Speaking of names, depending on the cavity and organ of interest, some of these membranes
will have unique names, like the pericardium surrounding the heart or the pleura which
surrounds the lungs.
But each of those structures does the same thing — they line a body cavity or the organs
within it.
The heart has a similar set up to the abdomen, a parietal layer, some space for a few milliliters
of serous fluid, and a visceral layer.
Then throw on a tough, fibrous outer layer around it and that’s really the only additional
structure.
Yes, these layers get fancy names, like the visceral layer is often called the epicardium,
but the structure is still similar to the other body cavities and membranes.
Then all of those layers wrap around heart muscle, or myocardium which is a special type
of muscle tissue.
But otherwise, the same concepts of layers of serous membrane still apply.
You just have to put some extra work into naming conventions.
Speaking of tissue, I kind of glossed over specific tissue terms like epithelial tissue
and connective tissue in this video, so I’ll have a video dedicated to the different types
of tissue and how to to tell them apart linked here.
Otherwise you can check out this playlist of other anatomy basics and make sure you’re
subscribed and hit the bell so you get notified when I post new videos.
Have fun, be good, thanks for watching.