S2 L2 Histology of Respiratory System

Question 1

Respiratory tract

• Two portions
• List which ‘structures’ are in each
• What are the sizes of lumen?

Answer 1

Conducting portion of respiratory tract = nasal cavity to bronchioles.
Respiratory portion of
respiratory tract
= respiratory bronchioles to alveoli.

The walls of the passageways become thinner as their lumens decrease in diameter.

Question 2

Epithelial changes in the Respiratory epithelium at each part

Answer 2

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Question 3

Histology of the cartilage of trachea compared to primary bronchi

Answer 3

Primary bronchi have a histology similar to that of the trachea, but their cartilage rings and spiral muscle completely encircle the lumen.

Question 4

Histology of the wall of trachea

Pseudostratified cilitated epithelium histology

Answer 4

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ciliated epithelium - Mucociliary escalator

Question 5

TEM of human tracheal epithelium

SEM of luminal surface of a bronchus

Answer 5

Question 6

SECRETIONS from the epithelium (E) and submucosal glands (G) of the trachea and bronchi contain

Histology of the secondary and tertiary bronchi

Answer 6

• Mucins, Water,
• Serum proteins,
• Lysozyme (destroys bacteria),
• Antiproteases (inactivate bacterial enzymes
• Lymphocytes contribute immunoglobulins (esp. IgA)

Question 7

Bronchus and bronchiole histology

Comparing the structure of a bronchus and bronchiole

Answer 7

Small Bronchus

Bronchiole

Cartilage

Small islands of cartilage +

No cartilage

Glands

Glands in submucosa +

No glands

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Question 8

Histology of a bronchiole

Answer 8

Question 9

Bronchioles and asthma

Answer 9

Absence of cartilage in walls of bronchioles can be problematic because it allows these air passages to constrict and almost close down when smooth muscle contraction becomes excessive.

Such bronchoconstriction can become excessive in asthma and cause more difficulty with expiration than inspiration (during expiration the bronchial walls are no longer held open by the surrounding alveoli).

Question 10

Club (Clara) cell

• What are these?
• Why is it important not to have goblet cells in narrow airways?

Answer 10

• As bronchioles get smaller, goblet cells give way to Club cells, interspersed between ciliated cuboidal cells.
  Club cells secrete a surfactant lipoprotein, which prevents the walls sticking together during expiration.
• Absence of goblet cells in these very narrow airways is important to prevent individuals from ‘drowning’ in their own mucus.

Question 11

Passageways opening onto alveoli

Answer 11

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Question 12

Histology (not magified) of smallest airways

Answer 12

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Question 13

Histology (magnified out) of aleolar sac and alveoli

Answer 13

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Question 14

Alveoli:

• Alveoli can open into…
• Alveolar walls have…

Answer 14

Alveoli can open into:

• a respiratory bronchiole
• an alveolar duct
• an alveolar sac
• another alveolus (via an alveolar pore)-

New alveoli continue to develop up to the age of 8 years when there are approximately 300 million.

Alveolar walls:

• have abundant capillaries
• are supported by a basketwork of elastic and reticular fibres.
• have a covering composed chiefly of type I pneumocytes.
• have a scattering of intervening type II pneumocytes.

Question 15

Alveoli:
- 2 types of cells

Answer 15

Type I cells (squamous) cover 90% of surface area and permit gas exchange with capillaries.

Type II cells (cuboidal) cover 10% of surface area and produce surfactant.

Numerous macrophages line alveolar surface (phagocytose particles).

Gas exchange occurs across blood-air barrier.

Question 16

Type II alveolar cell

• SEM image
• What particular organelle do they contain?

Answer 16

Lamellar bodies - produce surfactant