00:02
So after the trachea
we're going to branch
into what's known
as the bronchi.
00:07
The air passages are going to
undergo twenty three
orders of branching.
00:13
This branching is referred
to as the bronchial tree
because when you turn
it right side up,
it kind of looks like a tree.
00:22
From the top of
the bronchial tree,
we start with a conducting zone
and then it gives rise
to a respiratory zone.
00:31
In the conducting zone,
we're going to be conducting air
into the lower respiratory tract
and in the respiratory zone,
this is where gas exchange
is going to take place.
00:43
So in the conducting Zone
the trachea divides to
form the right and the left
main or primary bronchi.
00:53
Interestingly the
right main bronchus
is wider, shorter,
and more vertical
than the left.
01:00
And so if a person is
to inhale an object,
it's more likely to go into
the right main bronchus.
01:09
Each main bronchus
enters into the hilum
of one of the lungs either
the right or the left lung.
01:16
At this point they are
now going to branch
into the secondary bronchi
also known as the lobar bronchi.
01:24
The reason they
get this name lobar
is because each one
is going to correspond
to one of the lobes of the lung.
01:32
So there are three on the right
and two on the left.
01:36
Again, each lobar bronchus
supplies one of the
lobes on the lungs.
01:45
And the end of the
conducting zone
we are now going to go
into the tertiary bronchi
also known as the
segmental bronchi.
01:54
We call them segmental
because they start to divide
into multiple segments.
01:59
Each branch becomes
smaller and smaller
until we get to the point
where once we're less than
a millimeter in diameter.
02:07
We are now referring
to them as bronchioles.
02:11
At the very end of
the conducting zone,
are terminal bronchioles
get as small as less than a half
of a millimeter in diameter.
02:23
In the conducting zone
where we go from
bronchi to bronchioles
several different changes occur.
02:30
First, the support structures
of this area are
going to change.
02:35
The cartilaginous rings
that we started
with in the trachea,
are now going to
become irregular plates
and as we get to
the bronchioles,
we're going to replace the
cartilage with elastic fibers.
02:50
The epithelium is also
going to start to change.
02:53
Recall
that we start with a ciliated
pseudostratified columnar.
02:59
This is going to eventually
give way to cuboidal cells.
03:04
Also the cilia
and the goblet cells are
going to become more sparse.
03:10
So if we start with
the primary bronchi,
basically what we have
is that the beginning
we're starting with ciliated
pseudostratified columnar cells,
and then as we get to
the larger bronchioles,
this is going to
change into ciliated
simple columnar cells
that still contain goblet cells.
03:30
And then from there
we're going to as we get
to the smaller bronchioles.
03:35
We get ciliated cuboidal cells
that do not have
goblet cells at all.
03:40
And as we get to the
terminal bronchial
we have non ciliated
cuboidal cells.
03:48
Another change that occurs
is going to be the
amount of smooth muscle.
03:53
So as the cartilage disappears,
we're going to get
more smooth muscles
and this is going
to become important
because this is going
to help us to provide
substantial resistance to air
passage in the bronchioles.