smaller than it would normally be. In addition,
we may also have agenesis, failure of the
lungs to form altogether. This will be a result
of complex interactions between signaling
molecules. Now, in general, we are not going
into the complexities of molecular signaling
at this detailed level. So we merely note
that here, we have particular agents, for
instance, BMP-4, bone morphogenetic protein
4, which is responding to signals from the
mesoderm through the fibroblast growth factor
10 and transforming growth factor beta 1.
Another gene involved in the surrounding tissue
is one called sonic hedgehog. Really, all
I want to make clear here is that there are
complex patterns of tissue signaling that
take place. And a disturbance in the genetics
for any one of these could lead to the lung
failing to grow out or failing to bud properly.
Normally, of course, the placenta is dealing
with gas exchange during intrauterine life.
So the baby will continue to develop perfectly
normally even in the absence of lungs. And
it could be a unilateral condition on one
side of the body or bilateral on both sides
of the body. Now, fortunately, bilateral lung
agenesis is extremely rare because it is, of
course, incompatible with subsequent survival
after birth. So, let’s summarize what we’ve
covered in this lecture. First of all, we
looked at how lungs developed in the first
place, and then we focused on the maturation
of the lungs because in the case of the lungs,
the state of histological differentiation
is of absolutely vital clinical significance.
We looked at major abnormalities and clinical
problems that can arise when things go wrong
in lung development, and touched in some of
the ways in which one might recognize them.
For instance, dribbling milk from the mouth
on feeding or the abdomen extended on breathing.
Finally, we looked at the clinical significance
that some of these events might have during
the course of development. Thank you.