From Trachea to Terminal Bronchiole在线视频

Hi everyone!

Welcome to the world of clinical histology.

Today's sessions

will be from the

trachea to the bronchioles,

and finally to the terminal bronchiole,

which ends the conducting portion

of the respiratory system.

Again we will start with Huqi's case.

When she was in college,

she once had a cough

which lasted for a long time.

She often coughed with white sticky sputum.

Her symptom was worse at night

and her roommates also commented that

she had a strange noise while sleeping.

One night,

she suddenly woke up with

shortness of breath,

and was taken to

the emergency department.

She was diagnosed

to have bronchitis and bronchial asthma.

After a few days her symptoms improved

and she stopped the medication.

She had no further attacks.

After graduating from college,

she started to work and took up smoking.

Gradually,

this increased to one pack a day.

To explain the symptoms of bronchitis

and bronchial asthma，

we need to understand the

general structure of the trachea

and bronchial tree.

Okay,

let's take a look at the structure of

respiratory system again.

This diagram

shows a model of the bronchial tree.

We can see the conducting portion ends at

the terminal bronchioles,

the inhaled air would be

cleansed,

humidified and warmed

by the structures above.

As the branches of the bronchial tree

become finer,

their structures will also change.

When we go down the bronchial bundle,

the epithelium will change from

a pseudostratified ciliated

columnar epithelium

to a simple columnar epithelium

at the terminal bronchiole.

There are fewer

and fewer goblet cells in the epithelium.

The number of ciliated cells

also begins to decrease at this level

while the glands and cartilage

gradually start to decrease

from the lobular bronchus.

The structural changes

are closely related to

the functions of the bronchial bundle.

Firstly,

let's start with the trachea

that is below the larynx.

The left slide is the H&E-stained section

of the trachea.

We can see the C-shaped cartilage

in the adventitia

and the ring-shaped smooth muscle

on the inner surface of the cartilage.

At the innermost layer

we have respiratory epithelium

covering the cavity surface

We have already talked about these

in the previous session.

Then,

let's take a look at Huqi's case.

She was diagnosed

with acute bronchitis at age 20.

Most likely she had

chronic allergic reaction of

the upper respiratory tract,

with increased

secretion of the tracheal submucosal glands

and epithelial goblet cells,

but no bacterial infection.

At night,

the vagus nerve is activated

with increasing mucus secretion,

so her cough was worse when asleep.

Chronic allergy causes

sustained bronchial muscle contractions

which may lead to hypertrophy of

smooth muscles,

constricting the bronchial lumen.

Fortunately,

the bronchial tree at this level

still has the cartilage slices,

so that the bronchial lumen

is not completely blocked.

The bronchiole cartilage

becomes less as it goes down

and finally disappears

in the terminal bronchioles.

Meanwhile,

the smooth muscles

are increasingly more developed.

Try to think about the meaning

of the changes here.

Well,

when a person with hyper-reactive airways

in inhales allergens,

these smooth muscles will contract intensely,

hence narrowing the bronchiolar lumen.

Air traveling through these narrowed passages

will create turbulent airflow.

Clinically,

asthma often affects

the bronchioles and terminal bronchioles.

There is are no cartilages

in these parts.

The sudden contraction of

smooth muscles

may lead to complete blockage

of the already narrowed lumen.

This can explain

why Huqi suddenly woke up at night

feeling severely short of breath.

For some patients,

such attacks

of asthma may occur repeatedly

and could be fatal

if not promptly treated.

Finally,

let's summarize.

From the trachea

to the terminal bronchioles

we can see a gradual change in the

epithelium, goblet cells,

submucosal glands and smooth muscles.

These modifications

are associated with changes

in the tracheobronchial lumen

diameters at various levels,

as well as the different demands for

air warming, humidifying and cleansing.

If we can understand

the histological basis of these changes,

we can better appreciate their functions

and the causes of

common clinical conditions.