Respiratory System
Air is moved through the lungs by a ventilating mechanism, consisting of the thoracic cage, intercostal
muscles, diaphragm, and elastic components of the lung tissue.
Th e system is divided anatomically into structures of the upper and lower respiratory tracts. Functionally, the
system has two components:
A. The conducting portion (nasal cavities, nasopharynx, larynx, trachea, bronchi terminal bronchioles
B. The respiratory portion, where gas exchange occurs, consisting of respiratory bronchioles & alveoli
Nasal Cavity:
o Has external dilated vestibule and internal nasal cavity
o Skin of nose enters the nostrils into the vestibule and has sweat glands, sebaceous glands, and vibrissae
(hairs) that filter out material from air.
o The skin loses its keratinized nature in the vestibule and becomes pseudostratified columnar epithelium
before entering the nasal cavities.
o Nasal cavities are separated by the septum, and extending from each lateral wall are 3 boney
projections called conchae.
o The mucosa covering the nasal cavity has lamina propria that conditions inhaled air.
o IgA secretion from plasma cells in the lamina propria are found in nasal secretions.
o Middle and inferior conchae are covered with respiratory epithelium, while the roof of the nasal cavities
and the superior conchae are covered with olfactory epithelium.
Respiratory epithelium:
Ciliated pseudostratified columnar epithelium
Has 5 major cell types:
1. Ciliated columnar cells: most abundant
2. Goblet cells: granules of mucin glycoproteins
3. Brush cells: columnar cells with microvilli. They are chemosensory receptors resembling gustatory cells.
4. Small granule cells: part of the diffuse neuroendocrine system (DNES)
5. Basal cells: mitotically active stem and progenitor cells.
Olfactory epithelium:
Pseudostratified columnar epithelium
Has 3 major cell types:
, o Olfactory neurons:
Bipolar neurons
They form olfactory nerve when they pass through cribiform plate, Cranial nerve 1.
Synapse with other neurons in olfactory bulb
o Supporting cells:
Columnar
Have microvilli
o Basal cells:
Stem cells for other two types of cells
The lamina propria of olfactory epithelium possesses large serous glands, the olfactory glands (of
Bowman), which produce a constant flow of fluid surrounding the olfactory cilia.
o Paranasal sinuses: found in frontal, maxillary, ethmoid and sphenoid bones of the skull.
They are lined with thinner respiratory epithelium.
Its lamina propria contains few small glands
Nasopharynx: first part of the pharynx. It is lined with respiratory epithelium and its mucosa contains the medial
pharyngeal tonsil and the bilateral openings of the auditory tubes connected to each middle ear cavity.
Larynx:
o Reinforced by hyaline cartilage and elastic cartilage
o Participate in sound production
o The epiglottis (upper rim of larynx) prevents swallowed food or fluid from entering the passage.
o Its upper surface has stratified squamous epithelium
o Mixed mucous and serous glands are found in the lamina propria beneath the epithelium
Air is moved through the lungs by a ventilating mechanism, consisting of the thoracic cage, intercostal
muscles, diaphragm, and elastic components of the lung tissue.
Th e system is divided anatomically into structures of the upper and lower respiratory tracts. Functionally, the
system has two components:
A. The conducting portion (nasal cavities, nasopharynx, larynx, trachea, bronchi terminal bronchioles
B. The respiratory portion, where gas exchange occurs, consisting of respiratory bronchioles & alveoli
Nasal Cavity:
o Has external dilated vestibule and internal nasal cavity
o Skin of nose enters the nostrils into the vestibule and has sweat glands, sebaceous glands, and vibrissae
(hairs) that filter out material from air.
o The skin loses its keratinized nature in the vestibule and becomes pseudostratified columnar epithelium
before entering the nasal cavities.
o Nasal cavities are separated by the septum, and extending from each lateral wall are 3 boney
projections called conchae.
o The mucosa covering the nasal cavity has lamina propria that conditions inhaled air.
o IgA secretion from plasma cells in the lamina propria are found in nasal secretions.
o Middle and inferior conchae are covered with respiratory epithelium, while the roof of the nasal cavities
and the superior conchae are covered with olfactory epithelium.
Respiratory epithelium:
Ciliated pseudostratified columnar epithelium
Has 5 major cell types:
1. Ciliated columnar cells: most abundant
2. Goblet cells: granules of mucin glycoproteins
3. Brush cells: columnar cells with microvilli. They are chemosensory receptors resembling gustatory cells.
4. Small granule cells: part of the diffuse neuroendocrine system (DNES)
5. Basal cells: mitotically active stem and progenitor cells.
Olfactory epithelium:
Pseudostratified columnar epithelium
Has 3 major cell types:
, o Olfactory neurons:
Bipolar neurons
They form olfactory nerve when they pass through cribiform plate, Cranial nerve 1.
Synapse with other neurons in olfactory bulb
o Supporting cells:
Columnar
Have microvilli
o Basal cells:
Stem cells for other two types of cells
The lamina propria of olfactory epithelium possesses large serous glands, the olfactory glands (of
Bowman), which produce a constant flow of fluid surrounding the olfactory cilia.
o Paranasal sinuses: found in frontal, maxillary, ethmoid and sphenoid bones of the skull.
They are lined with thinner respiratory epithelium.
Its lamina propria contains few small glands
Nasopharynx: first part of the pharynx. It is lined with respiratory epithelium and its mucosa contains the medial
pharyngeal tonsil and the bilateral openings of the auditory tubes connected to each middle ear cavity.
Larynx:
o Reinforced by hyaline cartilage and elastic cartilage
o Participate in sound production
o The epiglottis (upper rim of larynx) prevents swallowed food or fluid from entering the passage.
o Its upper surface has stratified squamous epithelium
o Mixed mucous and serous glands are found in the lamina propria beneath the epithelium
