Lung在线视频

Hi everyone,

welcome to histology of the respiratory system.

Let's get on with the third topic-the lung.

In the previous two sections,

we have completed

how the inhaled air is cleaned,

humidified and warmed during inspiration,

and finally it comes to the lungs

for gas exchange.

We will now introduce the important structures

related to the gas exchange.

We will still use Huqi's story

to help you understand.

Last time we mentioned

that Huqi started working

and has become addicted to smoking.

Regarding her asthma,

there were occasional attacks

but they all resolved spontaneously.

Close to retirement age,

she began to cough

in the morning with white sputum,

and felt increasingly tired.

She went to the doctor

and her chest X-ray showed emphysema.

She was diagnosed

with chronic obstructive pulmonary disease

and advised to quit smoking.

In the last sections,

we have talked about the histologic structures

of the respiratory system,

such as smooth muscles, elastic fibers

and a variety of epithelial tissues

closely related to the particular functions.

Then,

what are the histological changes in emphysema?

To answer this question,

we need to know the structures of the alveoli

and the lung air-blood barrier.

Let's first review this diagram.

All the changes of epithelial connective tissues

in the respiratory system

are related to their respective functions.

The simple ciliated columnar epithelium

ends at the conducting portion

of the respiratory system.

Then,

starting from the respiratory portion,

the bronchioles are lined with

simple cuboidal epithelium

or simple squamous epithelium.

The surrounding tissues

only have a small amount of

smooth muscles and elastic fibers,

supporting the structure

of the entire respiratory portion.

Letter "R" in this picture goes

from the terminal bronchioles

to the respiratory bronchioles,

then to the alveolar ducts,

alveolar sacs and finally to the alveoli.

As you can see here,

from the respiratory bronchioles,

the lining cells

are of simple cuboidal epithelial type.

It consists of Clara cells

in the middle functioning as immune cells.

Small amount of connective tissues

and smooth muscles

are also found in the respiratory bronchioles

and the alveolar sacs,

The respiratory bronchioles branch

down into the alveolar ducts,

gradually appearing at the opening

of the alveoli.

At the end of these alveolar openings,

a small amount of smooth muscle is present,

forming a nodular structure.

The contraction of these smooth muscles

can facilitate gas exchange.

Further inside,

each alveolar sac

has more than a dozen alveolar openings.

No smooth muscle

at the end of the alveolar opening,

so no nodules are formed.

Then let's take a closer look at

Then let's take a closer look at

these alveolar epithelia,

which are simple squamous or cuboidal epithelia.

These alveolar cells

can be divided into type I and type II.

The alveolar epithelium is connected to

the underlying loose connective tissues.

They have many capillaries,

a small amount of smooth muscles,

collagen and elastic fibers,

as well as immune cells.

Shown in the picture is the alveolus.

Here we see the type I flat alveolar cells

covering about 95%

of the very thin (0.1-0.2um)

alveolar surface area.

Between these epithelial cells

are tight junctions,

which ensure that interstitial fluid

does not seep into the alveoli.

Type II alveolar cells produce surfactant,

which is a substance

that reduces the surface tension of the alveolus.

This slide shows the structure of the alveoli

under light microscope.

The blue arrows refer to type I alveolar cells,

and the green arrows

indicate type II alveolar cells.

Then let's take a look at the connective tissue

underneath the alveolar epithelium,

which we call the alveolar septum.

It contains an extensive capillary network

wrapped around the alveoli.

These capillaries

are joined by loose connective tissues

containing elastic and collagen fibers.

Finally,

we come to the air-blood barrier

where oxygen and carbon dioxide exchange.

This is the model of the barrier

composed of alveoli and capillaries.

We know that

the alveoli are covered with surfactant

and below are the alveolar epithelial cells

and basement membrane.

From the alveolar septum

to the capillary basement membrane

and endothelial cells,

the gas has to pass through a total of 6 layers.

Let's use the case of Huqi

as the summary of the respiratory system.

She had allergic rhinitis since the age of six.

Later,

she developed

a series of airway hypersensitive symptoms,

including chronic bronchitis and asthma.

She also had a long history of smoking.

These chronic processes will eventually lead to

the structural changes of respiratory system.

It started with impaired ciliary cell function,

then abnormal expulsion of secretions,

hyperplasia of goblet cells

and underlying glands

as well as increased secretions.

These changes were associated with

smooth muscle hypertrophy

or even hyperplasia,

and dissolution of cartilage slices,

the airway lumen becomes smaller

and may even collapse in serious cases.

These changes are gradual and progressive.

When Huqi was young,

she did not realize the consequences of smoking

and irregular asthma treatment.

However,

with aging and the influence of smoking

and other factors,

structural lung damage would occur.

By reviewing the whole development of this case,

we have also gone through the key points

of the respiratory system histology.

Also,

have you noticed that

Huqi is the pronunciation of

"breathing" in mandarin?

We hope that this story

can help you understand the relationship

between various structures

and functions of respiratory system histology,

and the importance of

early effective health education.

This would hopefully

enable a large number of patients

like Huqi to still maintain

a high-quality life after retirement.

And here are the references!