Histology of the Respiratory System

Question 1

The respiratory system is functionally divided into conducting and respiratory portions. State the constituents of the conducting portion, stating their role other than conducting air to/from the alveolar spaces.

Answer 1

nasal cavities, pharynx, larynx, trachea, principal bronchi, secondary/lobar bronchi, tertiary/segmental bronchi, terminal bronchioles

The bronchial tree: [Diagram 1] [Diagram 2]

Air conditioning: warming, moistening (humidification), filtering.

Question 2

The nasal cavity is divided into three regions. Name them.

Answer 2

(1) Nasal vestibule, anterior parts
(2) Respiratory region, inferior two-thirds
(3) Olfactory region, upper one third
[Diagram]

The olfactory mucosa is mainly restricted to the upper 1/3 of the nasal septum, the roof of the nasal cavity, and the superior turbinate.

Question 3

Briefly discuss the nasal vestibule.

Answer 3

✪ Lined by stratified squamous keratinized epithelium (like skin)
✪ Contains vibrissae, sebaceous glands

Question 4

State the cell types of the respiratory epithelium and their functions.

Answer 4

Ciliated columnar cells: Protective lining & waft particles.
Goblet (mucus) cells: Secrete the mucus (that trap particles).
Basal (stem) cells: Regeneration (give rise to other cells).
Granule (Kulchistky) cells: Neuroendocrine secretions (serotonin)
Brush cells: General sensations.

[Slide 1]

Note:
☯ In the lamina propria beneath the respiratory epithelium, there are large vascular channels called ‘swell bodies’ and they become engorged with blood alternatively to reduce the air flow in the nostril affected. This allows the affected nostril to recover and prevent desiccation.

Question 5

State the functions of the following:
(a) vibrissae in the nasal vestibule
(b) goblet cells
(c) glands in the lamina propria
(d) rich vascular network in the lamina propria (throughout the respiratory system)

Answer 5

(a) help trap large dust particles.
(b) produce mucus which traps particulate matter.
(c) produce a serous and mucoid secretion that humidifies/moistens the air and provides additional surface for trapping small particles respectively.
(d) provides an efficient mechanism (countercurrent relationship) that adjusts the temperature of the inspired air; provides enhanced transport of oxygen following absorption; delivers immune cells into this layer.
[Slide]

Question 6

State four cell types of the olfactory epithelium and their roles.

Answer 6

Olfactory receptor cells: 1st order neurons (bipolar cells)
Sustentacular cells: Structural and metabolic support
Basal (stem) cells: Regeneration (give rise to other cells)
Brush cells: General sensation

[Slide 1] [Slide 2]

Further notes:
☯ It appears yellows brown in a live specimen due to lipofuscin granules in the Bowman glands and epithelium.
☯ Lipofuscin granules are pigment-containing residues that accumulate within the cells as a result of the degradation of cellular components, particularly within lysosomes. The are often referred to as “aging pigment” due to their increased accumulation in cells over time. These granules are typically yellow-brown in color and contribute to the pigmentation of the olfactory mucosa.

Question 7

State the functions of the following in the nasal cavity:
(a) turbinate system
(b) thin-walled veins in lamina propria
(c) serous glands in lamina propria

Answer 7

(a) They increase the surface area of the cavities for warming, humidification and filtration of air as it passes to the lungs.
(b) comprise heat-exchange system
(c) increase humidity

Further notes:
One of the main reasons why air needs to be warmed in the respiratory tract is to optimize gaseous exchange in the alveoli. Gaseous exchange is more efficient when the air is warm and humid.

Question 8

State the type of epithelium in the:
(a) nasopharynx
(b) oropharynx
(c) laryngopharynx

Answer 8

(a) pseudostratified columnar ciliated epithelium with goblet cells
(b) non-keratinised stratified squamous epithelium
(c) non-keratinised stratified squamous epithelium

Question 9

The laryngeal wall consists of mucosa, cartilages and intrinsic muscles. State the type of epithelium of the mucosa.

Answer 9

Respiratory epithelium except at the lingual surface of epiglottis and true vocal cords which are lined by non-keratinized stratified squamous epithelium due to increased friction.

[Slide 1] [Slide 2] [Slide 3]

Further notes:
True vocal cords (vocal folds) vs False vocal cords (vestibular folds)
✪ The true vocal cords (vocal folds) are the actual sound-producing elements of the voice. They are composed of twin infoldings of mucous membrane stretched horizontally across the larynx. They contain muscle fibres, namely the vocalis muscle, which can tighten the cords. They vibrate and modulate the flow of air being expelled from the lungs during phonation.

✪ The false vocal cords (vestibular folds) do not play a direct role in sound production. They sit slightly superior to the true vocal cords and are part of the laryngeal vestibule. They are composed of mucous membrane and do not contain muscle.

[Image] [Diagram]

Question 10

State the type of cartilage of each of the laryngeal cartilages.

Answer 10

Elastic: epiglottis, cuneiform, corniculate, a portion of arytenoid
Hyaline: thyroid, cricoid, and the remaining portion of arytenoid

Question 11

What structures are present within the vocal folds?

Answer 11

thick bundles of elastic fibers (vocal ligament) and skeletal muscle (vocalis)

Question 12

State the four layers of the tracheal wall from within outwards.

Answer 12

(1) Mucosa: respiratory epithelium. Mucosa lies on a loose vascular lamina propria rich in elastic fibers and BALT (Bronchus Associated Lymphoid Tissue).
(2) Submucosa: has abundant mixed seromucous glands, highly vascularized.
(3) Musculocartilaginous layer: C-shaped hyaline cartilages (don’t forget, it has perichondrium) bridged by trachealis muscle posteriorly.
(4) Adventitia: a thin connective tissue that binds the trachea to adjacent structures
(5) [Slide 1] [Slide 2] [Virtual microscope 1] [Virtual microscope 2]

Question 13

State the proximo-distal changes in airway structure.

Answer 13

1. Size of tubes decrease.
2. Simplification of the lining epithelium.
3. Reduction in goblet cells.
4. Appearance of Clara cells in the smaller airways.
5. Glands in the lamina propria and submucosa diminish.
6. Smooth muscle content increases in the smaller airways.
7. Cartilage rings break into smaller plates.
8. Diminution of cilia.

Question 14

State the morphology of the extrapulmonary bronchus and intrapulmonary bronchus.

Answer 14

Extrapulmonary bronchus: similar to trachea, but with complete cartilage rings.
Intrapulmonary bronchus: irregular cartilage plates; circular layer of smooth muscles; narrower lumen.

Question 15

State the 5 layers of the bronchial wall.

Answer 15

1. Mucosa
2. Muscularis
3. Submucosa
4. Cartilage layer
5. Adventitia

Question 16

Make notes on the morphology of the primary bronchi.

Answer 16

✪ Lined by pseudostratified epithelium, which is shorter with fewer goblet cells.
✪ Dense lamina propria with a lot of elastic fibers, lymphoid tissue and mast cells.
✪ Reduced in size compared to the trachea.
✪ Smooth muscle layer between the lamina propria and submucosa.
✪ Bronchi have fewer seromucous glands in the submucosa.
✪ The cartilage rings start to break into plates.

Question 17

Make notes on the morphology of the secondary (lobar), tertiary (segmental) bronchi, and larger conducting bronchioles.

Answer 17

✪ Lined by columnar ciliated epithelium
✪ Have a reduced number of goblet cells
✪ Have a thin lamina propria with elastic tissue
✪ The cartilage rings start to break into plates
✪ Smooth muscle layer is more prominent
✪ Submucosa has even fewer glands [absent in bronchioles]
✪ Minimal cartilage [totally absent in the bronchioles]
✪ There is BALT, which is useful in the production of IgA class antibodies onto the mucosal surface for its defense

Question 18

Make notes on morphology of the smaller conducting bronchioles.

Answer 18

☯ Simple cuboidal epithelium, fewer ciliated cells.
☯ Presence of K (Kulchistky) cells.
☯ Fewer goblet cells, and they’re absent in terminal bronchioles. Now Clara cells replace the goblet cells.
☯ Smooth muscle layer remains prominent.
☯ No cartilage or submucous glands.

Note:
✪ In the lower respiratory tract, the airway possesses the ability to alter the caliber of the passages in response to autonomic influences. The amount of smooth muscle within the wall is maximal in the bronchioles for this purpose.

Question 19

The respiratory zone is also called the functional unit of the lung.
a) State the features of the respiratory zone.
b) State the components of the respiratory zone.

Answer 19

a) Features of the respiratory zone:
☯ several alveolar units
☯ thin blood-air tissue interface
☯ rich and extensive capillary network
b) Components of respiratory zone:
✪ respiratory bronchioles
✪ alveolar ducts
✪ alveolar sacs
✪ alveolar antra

Question 20

Briefly explain the morphology of the respiratory zone.

Answer 20

☯ Within the respiratory bronchioles, Clara cells become more prominent, replacing all goblet cells. These cells are thought to synthesize some component of surfactant.
☯ The alveolar ducts are long channels that are surrounded by some smooth muscle, collagen and elastic fibers.
☯ Alveolar sacs give rise to alveoli.
☯ Unlike the respiratory bronchioles, alveolar ducts and sacs, the alveoli are purely respiratory.

Question 21

Briefly describe pneumocyte type I cells.

Answer 21

☯ squamous alveolar cell
☯ establishes/contributes to the blood-air barrier
☯ for gas exchange via diffusion
☯ alveolar pores of Köhn allow equalization of pressure between alveoli and permit collateral air circulation

Question 22

Briefly describe pneumocyte type II cells.

Answer 22

☯ cuboidal alveolar cell
☯ contain phospholipid vesicles called lamellar bodies whose discharges contribute to surfactant layer
☯ give rise to pneumocyte type I (regeneration)

Question 23

Briefly discuss pneumocyte type III cells.

Answer 23

☯ Dust cells
☯ Pulmonary alveolar macrophages
☯ Clear debris
☯ Immune functions

Question 24

State the components of the thin blood-air barrier.

Answer 24

alveolar epithelium, capillary endothelium, fused basal lamina of the two [Diagram]