Hello, and welcome to this lecture on the
lungs and common abnormalities that occur
during the course of lung development. So we’re
going to look at how the lungs develop,
and particularly important, is understanding
the maturation of the lungs. Then we’ll
look at the major abnormalities and clinical
problems of lung development, and then we’ll
know how to recognize them. Finally, that
will lead us to their clinical significance.
So, let’s explore the early stages of lung
development. We’ve going to go back to this
stage where we’re looking at a cross-transverse
section through the embryo, the amniotic cavity
up above and the yolk sac down below. We can
see that the amniotic cavity is going to sweep
around as the embryo begins to fold and rise
up into the amniotic cavity. So a little later
on, we can see that the foregut and the hindgut
are beginning to develop, and it’s from
the foregut that the lung is going to develop
in its turn. We’ve marked in this one roundabout
where the lung will begin to develop, as the
yolk sac is beginning to diminish and form
a narrow stalk. What we can see is that this
is in the ventral part or the lower part of
the foregut. At a slightly later stage, the
embryo has completed this process of curving
into a C-shape. And roundabout where the neck
region is where the lung bud is formed in
relation to the rest of the foregut. In this
view, what we’ve done is to imagine that
we’ve taken the foregut and filled it with
some solid substance. We’re looking at all
the different components of the foregut itself.
So coming around from the neck, we can see
where the oesophagus is, and then growing
off eventually from that, there is the lung
bud that’s developing single lung bud, sometimes
known as the respiratory diverticulum.
At this stage, we’re about 22 days after fertilization.
This lung bud is growing ventrally and caudally
that is towards the tail. But of course, it’s
growing into a mesodermal surrounding tissue.
And although the lining of the lung bud is
derived from the endoderm, much of the support
ground material, and, of course, the blood
vessels will come from the mesoderm.
This process of bud formation could also be viewed
as one of the ridges growing in from the side
and pinching off the developing lung bud from
the oesophagus. Eventually, they will lie
so that this trachea, the developing lung,
will lie in front of the oesophagus.
Now, let’s focus on the lung bud itself. As we
go through the developmental process, what
we’ll see is that roundabout 28 days after
fertilization it begins to divide into two
separate buds. And you can see that one of those
buds, the right bud, is lying more towards
the tail than the left bud. So this is true from
very early stages. As the lung bud continues
to grow, so it will continue to divide, probably
when it reaches a set size. So by 33 days,
a further division is taking place. And what
we can see is that on the left-hand side,
we have two buds developing, whereas, on the
right-hand side, there are three buds developing.
This, of course, is so that there will be
room for the heart on the left-hand side.
This will be true in the adult lung also.
The branching process continues all the way
through development, gradually coming more
and more complex. For the lungs on the left,
there will be two lobes, and on the right,
there will be three lobes. On the right, these
are called the upper, middle, and lower lobes.
On the left, they are the upper and lower
lobes respectively. Each of these will give
rise to a bronchopulmonary segment, a major
part of the lung later on in development.
And this may be important in cancer where it might
be possible to remove just one bronchopulmonary
segment if that’s where a tumour should happen
to lie. Now, let’s look at the development