So the trachea then splits into two.
It splits into a right and a left primary bronchus.
So 'bronchi' is plural and 'bronchus' is singular.
So I'll just remove one of the lungs so we can take a look at the bronchi.
The place where the bronchus enters the lung is known as the hilum.
At the hilum, there's a couple of other structures which enter the lung.
So I've just brought the cardiovascular system and I'm going to rotate the model around posteriorly
and you can see the other structures that enter the lung.
So you've got the pulmonary veins and the pulmonary arteries which enter the lung at
the hilum.
So I've just switched to this diagram which shows the exact same view we're looking at.
We're looking at the posterior view, so you can see the trachea coming down here branching
off into the left and the right main bronchi.
You can see the pulmonary arteries at the top and the pulmonary veins inferiorly entering
into the lung at the hilum.
So you've got the pulmonary arteries in blue carrying deoxygenated blood from the heart,
to the lungs, to receive oxygen and you've got the pulmonary veins returning oxygenated
blood from the lungs to the heart.
So this diagram here just shows the hilum in a bit more detail.
You can see the structures entering this area called the hilum of the lung.
So just coming back to the bronchi, once they've entered the lung, they divide further.
They divide into lobar bronchi, which are also known as secondary bronchi.
And the lobar bronchi divide further into segmental bronchi.
So you've got the trachea dividing into the primary bronchus.
So you've got a right and left primary bronchus or main bronchus.
Then the primary bronchi divide into lobar bronchi, which are known as secondary bronchi.
And the secondary bronchi divide into tertiary bronchi, which are segmental bronchi.
So the bronchi just keep dividing and they end up in bronchioles, which are smaller and
lack cartilage.
And then these bronchioles eventually form alveolar ducts, which leads to alveolar sacs
and form alveoli, which are responsible for gas exchange and they have a huge surface
area for diffusion, have a rich blood supply and very thing, but we'll talk about that
in another tutorial.
So for now, just remember that the trachea divides into the right and left main bronchi,
which divide into secondary bronchi, which divide into tertiary bronchi.
So the secondary bronchi are called lobar bronchi because they supply the lobes of the
lung with air.
The right lung, which is this lung here, has three lobes.
You've got a superior lobe, a middle lobe and then an inferior lobe.
These lobes are separated by fissures.
So on the right lung, you've got a fissure, which separates the superior and middle lobes
and this is called the horizontal fissure.
And you've also got an oblique fissure because it runs obliquely and this separates the middle
from the inferior lobes and also the superior and inferior lobe at the back.
On the other side, the [left] lung, it only has one fissure.
So it's only got an oblique fissure, which separates a superior and inferior lobe.
So now that we know how many lobes there are in each lung, we know how many lobar bronchi
there must be.
There's only three right lobar bronchi and there are only two left lobar bronchi because
there's three lobes on that right and two lobes on the left.
So these lobes can actually be further divided into what is known as bronchopulmonary segments.
Each lung has ten bronchopulmonary segments.
These bronchopulmonary segments are supplied by the segmental bronchi, so the tertiary
bronchi.
So the lobar bronchi supply the lobes of the lungs and the segmental bronchi supply the
bronchopulmonary segments.
So you can see in this diagram the three lobar bronchi on the right and the two lobar bronchi
on the left.
So you can see them in different colors.
You've got the superior in green; yellow, you've got the middle lobar bronchus; and
in blue, you've got the inferior lobar bronchus.
And you've got the superior and inferior lobar bronchus in green and blue on the left side.
So the lungs themselves are surrounded by a pleural cavity.
You can see the cavity here in pink.
So the pleura or the pleural cavities are a serious membrane which line the lungs.
There's a visceral pleura and a parietal pleura.
So the visceral pleura lies very closely to the lung and adheres closely to the lung tissue.
The parietal pleural lines the thorax.
Both these pleural layers are continuous at the hilum.
So the visceral pleura and the parietal pleura is the pleural cavity.
This contains pleural fluid.
So this space between the visceral and the parietal pleura is only a potential space.
So in normality, these layers lie in very close contact and you've got this thin layer
of pleural fluid.
So I've just switched over to this cross-section of the lungs.
You can see anteriorly up here, posteriorly down here.
You've got the left lung and the left lung.
We'll just take a look at the -- so you can see the pleura in this diagram.
So you can see at the hilum, these two layers are continuous.
So you've got the outer layer, which is the parietal pleura, which lines the thorax.
And then the visceral pleural lies very closely to the lung and it goes into the fissures
and everything like that.
And then it is continuous with the parietal pleura at the hilum.
So this area, remember, where all these structures enter -- the bronchus, the bronchi, the pulmonary
arteries and pulmonary veins entering at the hilum.
So you can see how the viscera and parietal pleura are continuous with one another.
And then you've got this space between the two layers, which is the pleural cavity, which
contains pleural fluid.
So that's a very basic and broad overview of some of the structures in the respiratory
system.