Components of the Respiratory System

^ In relationship to lungs (listed in order from exterior to interior, i.e., the path of inspired air)

Intrapulmonary

1. Secondary bronchi

2. Bronchioles

3. Terminal bronchioles

4. Respiratory bronchioles

5. Alveolar ducts

6. Alveoli

Extrapulmonary

1. Nasal cavity

2. Pharynx

3. Larynx

4. Trachea

5. Primary bronchi

^ According to function (listed in order from exterior to interior)

Conducting Portion (Transports air from exterior)

1. Nasal cavity

2. Pharynx

3. Larynx

4. Trachea

5. Primary bronchi

6. Secondary bronchi

7. Bronchioles

8. Terminal bronchioles

Respiratory Portion (Involved with gas exchange)

1. Respiratory bronchioles

2. Alveolar ducts

3. Alveoli

Structure of "Typical" Respiratory Passageways

^ Conducting portion (nasal cavities through secondary bronchi)

• Mucosa (mucous membrane). Faces the lumen

♦ Respiratory epithelium. Pseudostratified with cilia and goblet cells.

♦ Lamina propria of loose connective tissue with blood vessels and nerves

♦ Deepest layer of mucosa may consist of:

■ An elastic lamina or

■ A muscularis mucosae or

• Submucosa. Dense irregular connective tissue with mucous and serous (mixed) glands

• Cartilage or bone

• Adventitia. Loose connective tissue forming the outer layer of the passageway

^ Structural transitions in walls and layers of the passageways from extrapulmonary passageways to alveoli

• Transitions

♦ Layers become thinner as passageways decrease in diameter.

♦ Epithelium decreases in height from pseudostratified to simple columnar to simple cuboidal to simple squamous.

♦ Goblet cells and mixed glands stop relatively abruptly at the junction of a secondary bronchus with a bronchiole.

Primary bronchus

Trachea

Larynx

Primary bronchus

Trachea

Larynx

Bronchi And Bronchioles

Secondary bronchi

Bronchioles figure 13.1. Conducting portion of the respiratory system.

Secondary bronchi

Bronchioles figure 13.1. Conducting portion of the respiratory system.

♦ Cartilage decreases in size, breaks up into plates, and stops relatively abruptly at the junction of a secondary bronchus with a bronchiole.

♦ Cilia are gradually eliminated.

• Results in the formation of the wall of an alveolus, where gas exchange occurs

♦ Epithelium is simple squamous

♦ Connective tissue core with numerous capillaries

Conducting Portion

Nasal Cavities (Extrapulmonary)

^ The nasal cavities can be subdivided into two regions, the olfactory and the non-olfactory regions.

^ Non-olfactory region

• Vestibules. The epithelium undergoes a transition from epidermis of skin with hairs to pseudostratified, respiratory epithelium.

♦ "Typical" mucosa but deepest layer is lacking (i.e., neither a muscularis mucosae nor an elastic lamina is present)

♦ Patency maintained by bones or cartilage.

LAYERS: Mucosa

Submucosal

Cartilage/bone AdventHIa figure 13.2. Layers and components of a "typical" respiratory passageway.

LAYERS: Mucosa

Submucosal

Lamina Propria Respiratory System

figure 13.2. Layers and components of a "typical" respiratory passageway.

• Olfactory region

♦ Upside-down, U-shaped area in posterior, superior region of each nasal fossa, extending over superior conchae and about 1 cm down nasal septum

♦ Composition of wall

- Epithelium is tall, thick, pseudostratified columnar with nonmotile cilia composed of

• Olfactory cells (neurons). Bipolar neurons that respond to odors. A single dendrite extends to the surface to form a swelling, the olfactory vesicle, from which nonmotile cilia extend over the surface. These cilia increase surface area and respond to odors.

• Support cells span the epithelium and support the olfactory cells.

• Basal cells are located on the basal lamina and serve as reserve cells for the epithelium.

- Deepest layer of mucosa is not present, so the lamina propria blends with the submucosa. This connective tissue layer contains Bowman's glands, serous glands whose watery secretions flush odorants from the epithelial surface.

■ Patency maintained by bone.

Larynx (Extrapulmonary)

^ Composition of the wall of the larynx

♦ Epithelium

■ Pseudostratified with cilia and goblet cells in most areas

■ Stratified squamous moist over true vocal folds and much of epiglottis because of friction incurred in these areas

♦ No muscularis mucosae or elastic lamina, so lamina propria is continuous with submucosa.

• Submucosa with mixed glands (except in true focal fold)

• Cartilages maintaining patency are numerous, uniquely shaped and are either hyaline or elastic. The larger cartilages are the epiglottis, thyroid, and cricoid.

• An adventitia is present.

^ Vocal apparatus. Modification in the larynx composed of two pairs of horizontally positioned mucosal folds located on the lateral walls of the larynx

• False vocal folds. More superior in location. Resemble the wall of a "typical" respiratory passageway except the deepest layer of the mucosa is absent (no muscularis mucosae nor elastic lamina).

• The ventricle, a space, separates the false from the true vocal folds.

• True vocal folds

♦ Are lined by a stratified squamous moist epithelium and its lamina propria

♦ A vocal ligament of dense regular elastic connective tissue is located at the edge of the fold, keeping the rim of the fold taut.

♦ Vocalis muscle, skeletal muscle, lies beneath each true vocal fold. This muscle alters the shape of the vocal fold and aids in phonation.

Trachea and Primary Bronchi (Extrapulmonary)

^ The trachea and primary bronchi are identical in structure and will be considered together.

^ Mucosa

• Epithelium pseudostratified with cilia and goblet cells with a very prominent basement membrane

• Lamina propria of loose connective tissue

• Elastic lamina of longitudinally arranged elastic fibers ^ Submucosa with mixed glands

^ C-shaped cartilage rings maintain patency; trachealis muscle

(smooth) interconnects the open ends of the tracheal rings. ^ Adventitia is present.

Secondary Bronchi (Intrapulmonary)

^ The secondary bronchi

• Are the first intrapulmonary structures; a secondary bronchus supplies each of the three lobes of the right lung and the two lobes of the left lung.

• Are similar to, but diminished in size from, the primary bronchi ^ Mucosa

• Epithelium, pseudostratified with cilia and goblet cells

• Lamina propria contains numerous, longitudinally arranged elastic fibers.

• Muscularis mucosae of smooth muscle fibers arranged in crisscrossing bands

^ Submucosa with mixed glands ^ Patency maintained by plates of hyaline cartilage. ^ Adventitia is present.

Bronchioles (Intrapulmonary)

^ Walls of bronchioles continue to decrease in size. The greatest changes in histology occur in the walls of the bronchioles as glands and cartilage are eliminated.

^ Mucosa

• Epithelium

♦ Pseudostratified with cilia and goblet cells in largest bronchioles that decreases to:

♦ Simple columnar with cilia in smallest bronchioles (terminal bronchioles), but no goblet cells persist.

♦ Clara cells are present in terminal bronchioles.

■ Tall, dome-shaped, nonciliated cells

■ Possess numerous secretory granules whose contents aid in lowering surface tension of the terminal bronchioles, thus aiding in inspiration

• Lamina propria contains numerous, longitudinally arranged elastic fibers.

• Muscularis mucosae. Greatest development of smooth muscle (crisscrossing bands) in relationship to thickness of wall of all respiratory passageways

^ Submucosa contains no glands.

^ No cartilages or bones support bronchioles; therefore, submucosa and adventitia form a single connective issue layer.

Respiratory Portion

Primary Function

^ Gas exchange occurs in the alveolus. Therefore, an alveolus must be an integral part of all the passageways of the respiratory part of the respiratory system.

Alveolar Duct

Alveolar ducts Alveolar sac Alveoli figure 13.3. Components of the respiratory portion of the respiratory system.

Alveolar ducts Alveolar sac Alveoli figure 13.3. Components of the respiratory portion of the respiratory system.

Respiratory Bronchioles

^ Respiratory bronchioles continue to decrease in diameter and in thickness of their walls.

^ Mucosa. Simple cuboidal epithelium with a few sparsely scattered cilia and Clara cells

• Elastic fibers in lamina propria

• Muscularis mucosae of smooth muscle

^ Alveoli bulge from wall (i.e., lumen of alveolus is continuous with lumen of respiratory bronchiole).

Alveolar Ducts

^ An alveolar duct is formed as the alveoli in a respiratory bronchiole increase in number, thereby decreasing the amount of wall that is present.

• At the level of the alveolar duct, the "wall" is reduced to a series of rings framing the entrance to an alveolus or a group of alveoli (alveolar sac).

• When sectioned, these rings resemble knobs to which the alveoli are attached.

• Simple cuboidal epithelium

• Elastic fibers and smooth muscle in "knobs"

• Alveoli bulge from the framework formed by the knobs.

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Responses

  • Anke Decker
    Are secondary bronchi intrapulmonary?
    8 years ago
  • Pasquale
    What is the lamina propria of the respiratory system?
    8 years ago
  • arnor
    Are secondary bronchii intrapulmonary?
    8 years ago

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