Now, the control center.
And there is quite a bit of detail here. Let
me just set it up for you so that we will
refer to the different components of this
when the time is right. We will take a look
at, well, we have the motor area and the sensory
cortex. I would like for us to pay attention
on your far right side where it says sensory cortex.
Okay. Now, in physiology, would you please
tell me, what is the most important chemoreceptor?
Is it central or peripheral? Central. Good.
Right now, as you are sitting there, watching
me, perhaps. Me, right now, it is my central
chemoreceptors that are always going to then
detect whom? Oxygen or carbon dioxide? What
are the central chemoreceptors more
sensitive to? Carbon dioxide changes.
Apparently, carbon dioxide. Remember,
on your arterial side, what's your PCO2? At 40,
right? Whereas on the venous side, what is
PCO2? Only 7, excuse me, 47. So, there is
only a difference of 7 there. Okay, so, carbon
dioxide is very important in terms of
sensing or being sensed by chemoreceptor, central
type. So, sensory cortex is then going to sense
the carbon dioxide that is in your blood,
but how does it do it? Your chemoreceptors
are located in the medulla. And in the medulla,
it's going to measure the cerebrospinal fluid.
Correct? Cerebrospinal fluid. And what do
you know about carbon dioxide? Why is there
only difference of 7 between the arterial
and the venous side? Because carbon dioxide,
how quickly does it diffuse across the membrane?
Like that. Carbon dioxide and carbon monoxide
is even faster, isn’t it? So, oxygen is
pretty good in terms of diffusion, but
what’s the heck of a lot faster is
going to be carbon dioxide and
later on, we will talk about carbon monoxide.
So carbon monoxide, which we are either trying
to blow off or if you are retaining it, well,
it is in the blood and so, therefore, it passes
across the blood brain barrier and is then
sensed by the central chemoreceptors. Is that
clear? Once that occurs then what happens?
It is going to then trigger through the motor
cortex, come over to your left now. In the
motor cortex, see where it says chemoreceptors,
it's hungry for air, because now, it sensed
an increased amount of carbon dioxide. How
did that occur? Maybe there is dyspnoea.
You are holding on to carbon dioxide. What
was that called? Hypercapnia or hypercarbia.
What's your level? Greater than 40. Are you building
upon the foundation that we are placing for
you? Good. So now, this is sensed by the
central chemoreceptors through your blood
brain barrier in the cerebrospinal fluid and
as soon as you hear about carbon dioxide,
what’s the formula that you are thinking?
Good. Carbonic anhydrase, aren’t you? Carbon
dioxide plus water, with the help of carbonic
anhydrase, will then yield your bicarb and
your hydrogen. So hence, carbon dioxide equals
hydrogen, hence a decrease in pH. Lot of stuff
there and as you can see here, it's
integration making sure that you understand
what is triggering that air hunger. And once
you get that air hunger going, then you are
going to start breathing as long as you have
proper muscles that are working. So, what
you are seeing in the bottom portion there
would be the most important muscle obviously,
just breathing back and forth will be your diaphragm.
When your diaphragm contracts, which direction?
Down. Good. And when you are expiring, you
are exhaling, it's passively moving up, diaphragm.
But, then you also have involvement of intercostal
artery, excuse me, intercostal muscles and
so forth. Sternocleidomastoid, that will
become important to us, when we talk
about a condition that a child might be suffering
from known as status asthmaticus. And why it
is so important to make sure that you understand
when these muscles are kicking in and why.
After muscle fatigue, your patient might
die and you don’t want that on your clock.
Let's continue. So, pulmonary problems, dyspnoea.
Cardiac problems, we just talked about this.
Pulmonary problems may result in edema. What
kind? Exudate, because of increased capillary
permeability. Cardiogenic, could result in
dyspnoea. Of course, give me some examples.
Left-sided heart failure, mitral stenosis.
Metabolic disturbances. What about the medulla?
What if the individual is taking an opiod,
okay, a narcotic. What happens now?
The respiratory center in the medulla has
been knocked out. It's gone. What do you end
up having? The patient has hypoventilation.
Welcome to CNS issues. Anxiety, absolute panic
attacks, anemia, lack of hemoglobin, exercise,
well, that would be normal. So, dyspnoea could
occur even with enough exercise, in which
what happens? The skeletal muscles are really
starving for oxygen. It's a nice little list
here to go through different problems or differentiation