00:00
Now look at this thymus gland.
00:02
It's located in the chest
behind the breastbone.
00:06
Now it's the biggest in little kids.
00:08
Now when you're first born,
it's pretty good size,
compared to the rest
of the size of your body.
00:12
It keeps growing gradually
until you reach puberty,
and then it gets smaller.
00:17
Yeah, but here's the bad news.
00:18
One more thing that gets replaced
by fat in your body.
00:22
So a thymus gland,
it's biggest when I'm a little kid,
keeps growing gradually until puberty,
and then it gets smaller
and is replaced by a fat.
00:31
Okay, that's normally what happens
with a thymus gland.
00:35
But throughout childhood,
it plays an important role
in helping the immune system develop.
00:40
So the thymus gland is a good guy,
because it's responsible for helping
make T lymphocytes or T cells.
00:48
So when you're looking
at the white cell count,
these are our fighters,
these are our defenders.
00:54
Because they're a very specific type
of white blood cell
that protects us
from viruses and infections.
01:00
When a patient is HIV positive
or then develops AIDS,
that means I've got
an opportunistic infection
and a low CD4 T cell count
less than 200.
01:11
So this is where these very specialized
white cells come from,
the thymus gland.
01:16
And, thankfully,
that's why we call them the T cells
because that's a little easier
to remember.
01:21
Okay, that's a lot of talk
about a thymus gland.
01:25
Pause the video for just a second
and I want you to write down
three quick facts
that you remember
about the thymus gland
without looking at your notes.
01:39
Okay, welcome back.
01:41
Remember, pause, and reflect,
and writing things down
really help you gain
mastery of that information.
01:48
Now we're going to talk
about the thymus gland in adults
because many adults
with myasthenia gravis,
their thymus gland didn't gradually
get smaller and replaced by fat,
it remains large.
02:00
So people with this disease,
typically have these clusters
of immune cells in their thymus gland,
similar to lymphoid hyperplasia.
02:08
Now, usually, that only
happens in the spleen and the lymph nodes
when someone has some
super active immune response.
02:14
But people with myasthenia gravis
sometimes have the same kind of activity
in their thymus gland.
02:21
Now some individuals with myasthenia gravis
develop a thymoma,
and I really have to think
before I say that word
because it's a tongue twister.
02:30
But a thymoma is a tumor
of the thymus gland.
02:34
Okay, so right away you've got the idea
that the thymus gland in adults
with myasthenia gravis is different.
02:42
Now how is it different?
It didn't become smaller
and replaced by fat
and sometimes it has this hyperplasia,
it gets really big.
02:50
Much like our spleen and lymph nodes do
in an active immune response.
02:55
Well, that's kind of starting
to make sense, isn't it?
Because we know
this is a autoimmune disorder,
we know that thymus gland
isn't working like it normally does.
03:03
It's doing some kind of different things,
going a little bit rogue.
03:06
And that's why the patient
is having a problem.
03:09
Now the thymomas
are usually harmless,
but it's something your healthcare provider
will keep a close eye on
because they can become cancerous.
03:18
So in myasthenia gravis,
the thymus gland gets bigger,
much like other organs do
in an acute immune response.
03:26
Some people with myasthenia gravis
develop thymomas
and these should be benign,
but they could actually turn cancerous.
03:34
So before we move forward,
make sure you have straightened your mind
what a normal thymus gland does
as you age,
and how it's different in a patient
with myasthenia gravis.
03:47
So we're gonna view that
one more time.
03:49
The thymus gland plays a role
in myasthenia gravis,
but we're not exactly sure what.
03:54
We just kind of laid down for you
that, look, it's different,
we know it looks different,
its size is different
and we're pretty sure
it plays a key role in myasthenia gravis.
04:04
See, here's what the theory is,
scientists think the thymus gland
may give some incorrect instructions
to the immune cells,
meaning--
Remember that thymus gland
makes those really specialized white cells,
those T cells,
and we think the thymus gland
in the case of myasthenia gravis patients
is giving some bad instructions
to those developing immune cells
that causes their immune system
to attack its own cells and its tissues,
and gives those acetylcholine receptor
antibodies.
04:34
And that sets you up for the stage
for attack on neuromuscular transmissions.
04:38
So we told you what we kind of think
is happening, right?
That thymus gland is telling
these developing cells
or giving them some bad instructions,
and that's what ends up--
At the end, the body
misunderstanding what those cells are
and attacking them,
creating antibodies
that blocks the transmission
and the patient's ability
to move their muscles.