We will begin our look at respiratory system development
by starting with the upper airway
and then moving into the area that carries air to the lungs
and then development of the lungs themselves.
Now one thing that's important
when we talk about the respiratory system
is to note that respiratory system defects can also cause cyanosis.
Now it's very easy to think of the heart
and malformations of the heart
being the only thing that causes bluish tinting
and cyanosis in the infant,
but respiratory malformations can do the same thing.
Sometimes that cyanosis is present at all times
and doesn't really depend on what the patient is doing.
Other times, it only manifest when the patient is exerting
him or herself, or can only sometimes be manifest
when the patient is feeding
and forced to breathe through the nose
and unable to breathe through the mouth.
So you may recall from our discussion of development of the face
that the frontonasal prominence
is gonna grow inferiorly and form the nose, the philtrum of the lip,
as well as part of the palate.
One thing that occurs in this process
is that we're going to have nasal placodes
form on either side of the frontonasal prominence
and they're gonna deepen and actually form the nostrils and the nasal cavities.
So if we take a sagittal view of the developing face,
we can see that these nasal sacs have moved into the face
and were kind of paralleling the oral cavity.
They're separated by the primary palate
and the thin sheet of tissue called the oronasal membrane.
It's separating the oral and nasal cavities.
As the nasal cavities deepen,
that membrane get's stretched thinner and thinner,
and is eventually going to rupture.
And it ruptures partially a little bit at a time
but eventually we wind up with the connection
of the nasal cavity back to the pharynx
and that's what allows us to breathe through our nose,
but also breathe through our mouth whenever necessary.
As development proceeds, a plug of material from the epithelium
is gonna close off the nasal cavity and as that's occurring,
Cranial Nerve I, has olfactory cells,
nerve cells growing down in the upper third of the airway
and forming the respiratory portion of the olfactory tracts.
We've got the olfactory epithelium,
sensing smells that comes in the nose
and translating that to the brain through the olfactory bulb.
As all these is proceeding,
the hard palate forms, the soft palate stretches out,
and the connection of the nasal cavity to the pharynx is maintained.
That connection is known as a choana.
You've got two choanae; one in the left, one on the right,
and they're separated by the nasal septum.
You have a single oral cavity that's also connecting to the pharynx,
and that connection is vitally important
because without this choanae,
we're not able to breathe through our nose
and get air further down towards our larynx.
If we have failure of the oronasal membrane,
to completely rupture,
we have atresia of the choanae,
meaning, that we don't have a connection
from the nasal cavity to the pharynx.
Choanal atresia is one of the hallmarks
to what is known as CHARGE Syndrome.
The C is for Coloboloma of the iris.
H, for heart defects;
A, is for choanal atresia;
R, for growth retardation or growth delay;
G, for genital and urinary malformation;
And E, for inner ear malformations.
And essentially, if you see a combination of these structures having problems,
that's gonna be CHARGE Syndrome,
and choanal atresia is one of the major problems associated with it.
Now, why is choanal atresia a problem?
If you don't have a connection from your nasal cavity to your pharynx,
it means you're unable to breathe through your nose.
Now, if this happened only on one side,
You'd probably be okay because you'd still have one nasal cavity
allowing air to move in to your larynx, but bilateral choanal atresia
means that every time an infant attempts to feed,
it's gonna be unable to breathe.
And so it's gonna have to feed quickly and then break off
and work to get some air into its lungs
because its gonna be unable to breathe while feeding
and may even become cyanotic when attempting to feed.
This affects roughly 1 in 8000 live births
and it's more prevalent in female infants than males.
Fortunately, surgery can be done to open up the choanae,
Although, if there's a significant thickening or bony oronasal membrane,
that surgery may be a little more pronounced
than simply rupturing a thin membrane.
Thank you very much
and we'll move on discuss further segments of the respiratory system.