Junqueira’s Basic Histology Text and Atlas, 16th Edition
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
Chapter 17 The Respiratory System ▪ Part of the diffuse neuroendocrine system (DNES).
• Exchange of O2 and CO2 to and from the blood. o Basal cells
• Ventilating mechanism moves air through the lungs which consists of the thoracic ▪ Stem cells that give rise to progenitor cells.
cage, intercostal muscles, diaphragm, and elastic components of the lung tissues. Olfactory Epithelium
• The system can be divided anatomically into the upper and lower respiratory • Specialized region of mucous membrane that contain olfactory chemoreceptors,
tracts. covering the superior conchae at the roof of the nasal cavity.
• Functionally, the system can be divided into two components: • This pseudostratified columnar epithelium has three major cell types:
o Conducting portion o Olfactory neurons
▪ Cleans and humidifies air. ▪ Bipolar neurons with nonmotile cilia.
▪ Provide conduits for air movement. ▪ The axons of these cells leave to the brain through the
▪ Ensure uninterrupted supply of air. foramina of the cribriform plate of the ethmoid bone and will
o Respiratory portion form the olfactory nerve (CNI).
▪ Gas exchange. o Supporting cells
▪ Alveoli is the cellular site of gas exchange. ▪ Cell with supportive roles but not well understood.
Nasal Cavities ▪ Express abundant ion channels.
• Left and right nasal cavities have two components, the external, dilated vestibule o Basal cells
and the internal nasal cavity. ▪ Stem cells for the olfactory neurons and supporting cells.
• Skin enters the nares partway into the vestibule and includes sweat glands, • Lamina propria has serous olfactory glands (of Bowman) that produce a constant
sebaceous glands, and coarse, moist vibrissae that filter particulate material. flow of fluid surrounding the olfactory cilia.
• Epithelium in the vestibule loses its keratinized nature and transition to typical Paranasal Sinuses
pseudostratified columnar epithelium which also lines the nasal cavity. • Bilateral cavities in the frontal, maxillary, ethmoid, and sphenoid bones.
• Nasal cavities are two cavernous chambers separated by the osseous nasal septum. • Lined with thinner respiratory epithelium with fewer goblet cells.
o Three bony, shelf-like projections are present in the lateral walls of the • Communicate with the nasal cavities through small openings and the mucus they
nasal cavities called conchae (superior, middle, and inferior conchae) produced are moved into the nasal passages by the activity of the cilia.
o Lamina propria conditions the air. Loops of capillaries near the epithelial Pharynx
surface warm the air and the small seromucous glands humidify the air. • Divided into three regions:
o Thin mucous layer trap and remove particles and microbes. o Nasopharynx
o Epithelium of the middle and inferior conchae is respiratory epithelium ▪ Left and right nasal cavities open posteriorly in the
while the roof nasal cavities and the superior concha is olfactory nasopharynx.
epithelium. ▪ Lined with respiratory mucosa which contains medial
Respiratory Epithelium pharyngeal tonsil and openings of the two auditory tubes.
• Ciliated pseudostratified columnar epithelium. o Oropharynx (Throat)
• This epithelium has five major cell types with thick basement membrane: ▪ Posterior part of the oral cavity and connects with the superior
o Ciliated columnar cells nasopharynx.
▪ Most abundant cell type. ▪ Mucosa of nonkeratinized stratified squamous epithelium and
▪ Ciliated cells. includes the palatine and lingual tonsils.
o Goblet cells o Laryngopharynx
▪ Numerous cells that secrete mucin. ▪ Short, narrow region caudal to the oropharynx and continues
o Brush cells at its inferior end with both the larynx and esophagus.
▪ Columnar cells that bear sparse, blunt microvilli. ▪ Lined with of nonkeratinized stratified squamous epithelium.
▪ Chemosensory receptors resembling gustatory cells. Larynx
o Small granule cells (Kulchitsky cells) • Short passageway for air between the pharynx and the trachea.
1 | The Respiratory System
, Junqueira’s Basic Histology Text and Atlas, 16th Edition
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
• Walls are reinforced with hyaline cartilage (thyroid, cricoid, and the inferior • Trachea divides into two primary bronchi that enter each lung hilum along with
arytenoid) and smaller elastic cartilages (epiglottis, cuneiform, corniculate, and lymphatic and blood vessels.
superior arytenoid). • Three secondary (lobar) bronchi in the right lung and two in the left lung, supplying
• Maintains an open airway and participate in phonation. each pulmonary lobe.
• Epiglottis • Secondary bronchi again divide, forming the tertiary (segmental) bronchi. Tertiary
o Flattened structure projecting from the upper rim of the larynx. bronchi and its smaller branches constitute a bronchopulmonary segment. These
o Prevent swallowed food or fluid from entering the air tubes. segments are import in surgical resection of diseased lung tissue without affection
o Lingual surface is lined with stratified epithelium while the laryngeal nearby healthy tissue.
surface undergoes transition to respiratory epithelium at variable points. • The terminal branches of the smaller bronchi are called bronchioles and each enters
o Mixed serous and mucous glands are present in the lamina propria. a pulmonary lobule, where it branches to form five to seven terminal bronchioles.
• Two pairs of folds separated by a narrow space or ventricle are seen below the • Histological organization of the epithelium and lamina propria of the smaller
epiglottis and laryngeal vestibule. bronchi and bronchioles gradually becomes more simplified.
o Vestibular folds Bronchi
▪ Upper pair of folds and are immovable. • Mucosa of larger bronchi is structurally similar to the tracheal mucosa except for
▪ Partly covered with respiratory epithelium. the organization of cartilage and smooth muscle.
o Vocal folds (cords) • The lumen of primary bronchi is completely encircled by cartilage rings. As the
▪ Lower pair of folds and are movable important for phonation. bronchial diameter decreases cartilage rings are gradually replaced with smaller
▪ Lined with nonkeratinized stratified squamous epithelium that isolated plates of hyaline cartilage.
protects the mucosa from abrasion and desiccation. • Lamina propria is abundant in small mucous and serous glands, and crisscrossing
▪ Vocal ligament, a dense regular bundle of elastic CT, supports bundles of spirally arranged smooth muscle and elastic fibers.
the free flaps of each vocal fold. • Contraction of this muscle layer is responsible for the mucosal folds evident in the
▪ Vocalis muscle are present in the deep mucosa that allow each bronchial mucosa.
vocal fold to be moved. Bronchioles
▪ During phonation, the vocalis muscle adducts the vocal folds • Intralobular airways with diameters of 1 mm or less formed after the tenth
together and the rima glottidis, opening between the vocal generation of branching.
folds, narrows and causes the vocal folds to vibrate.
• Lack mucosal glands and cartilage supports but reinforced with dense CT
▪ Sound qualities are altered by the changing the tension on the
associated with the smooth muscle.
vocal folds, width of the rima glottidis, and the volume of air
• Larger bronchioles are lined with respiratory epithelium with decreased height and
expelled.
complexity becoming ciliated simple columnar or simple cuboidal epithelium in
Trachea
the smallest terminal bronchioles.
• A 10-12 cm long air tube lined with respiratory mucosa.
• The ciliated epithelial lining of the bronchioles begins the mucociliary apparatus
• Lamina propria contains numerous seromucous glands that produce watery mucus.
important in clearing debris and mucus.
• Walls are reinforced with C-shaped rings of hyaline cartilage between the • The cuboidal epithelium of terminal bronchioles consists:
submucosa and adventitia to keep the tracheal lumen open. o Largely of club cells (bronchiolar exocrine cells or previously called the
• Open ends of the cartilage are on the posterior side where the esophagus is situated. Clara cells) with various functions, such as:
This area is bridged by a smooth muscle bundle, the trachealis muscle. ▪ Secretion of surfactant lipoproteins and mucins.
• Trachealis muscle relaxes during swallowing allowing the esophagus to bulge into ▪ Detoxification
the lumen of the trachea. ▪ Secretion of antimicrobial peptides and cytokines.
• This muscle strongly contracts during cough reflex to narrow the tracheal lumen o Chemosensory brush cells
and provide increased velocity of the expelled air. o DNES small granule cells
Bronchial Tree and Lung o Small population of stem cells
Respiratory Bronchioles
2 | The Respiratory System
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
Chapter 17 The Respiratory System ▪ Part of the diffuse neuroendocrine system (DNES).
• Exchange of O2 and CO2 to and from the blood. o Basal cells
• Ventilating mechanism moves air through the lungs which consists of the thoracic ▪ Stem cells that give rise to progenitor cells.
cage, intercostal muscles, diaphragm, and elastic components of the lung tissues. Olfactory Epithelium
• The system can be divided anatomically into the upper and lower respiratory • Specialized region of mucous membrane that contain olfactory chemoreceptors,
tracts. covering the superior conchae at the roof of the nasal cavity.
• Functionally, the system can be divided into two components: • This pseudostratified columnar epithelium has three major cell types:
o Conducting portion o Olfactory neurons
▪ Cleans and humidifies air. ▪ Bipolar neurons with nonmotile cilia.
▪ Provide conduits for air movement. ▪ The axons of these cells leave to the brain through the
▪ Ensure uninterrupted supply of air. foramina of the cribriform plate of the ethmoid bone and will
o Respiratory portion form the olfactory nerve (CNI).
▪ Gas exchange. o Supporting cells
▪ Alveoli is the cellular site of gas exchange. ▪ Cell with supportive roles but not well understood.
Nasal Cavities ▪ Express abundant ion channels.
• Left and right nasal cavities have two components, the external, dilated vestibule o Basal cells
and the internal nasal cavity. ▪ Stem cells for the olfactory neurons and supporting cells.
• Skin enters the nares partway into the vestibule and includes sweat glands, • Lamina propria has serous olfactory glands (of Bowman) that produce a constant
sebaceous glands, and coarse, moist vibrissae that filter particulate material. flow of fluid surrounding the olfactory cilia.
• Epithelium in the vestibule loses its keratinized nature and transition to typical Paranasal Sinuses
pseudostratified columnar epithelium which also lines the nasal cavity. • Bilateral cavities in the frontal, maxillary, ethmoid, and sphenoid bones.
• Nasal cavities are two cavernous chambers separated by the osseous nasal septum. • Lined with thinner respiratory epithelium with fewer goblet cells.
o Three bony, shelf-like projections are present in the lateral walls of the • Communicate with the nasal cavities through small openings and the mucus they
nasal cavities called conchae (superior, middle, and inferior conchae) produced are moved into the nasal passages by the activity of the cilia.
o Lamina propria conditions the air. Loops of capillaries near the epithelial Pharynx
surface warm the air and the small seromucous glands humidify the air. • Divided into three regions:
o Thin mucous layer trap and remove particles and microbes. o Nasopharynx
o Epithelium of the middle and inferior conchae is respiratory epithelium ▪ Left and right nasal cavities open posteriorly in the
while the roof nasal cavities and the superior concha is olfactory nasopharynx.
epithelium. ▪ Lined with respiratory mucosa which contains medial
Respiratory Epithelium pharyngeal tonsil and openings of the two auditory tubes.
• Ciliated pseudostratified columnar epithelium. o Oropharynx (Throat)
• This epithelium has five major cell types with thick basement membrane: ▪ Posterior part of the oral cavity and connects with the superior
o Ciliated columnar cells nasopharynx.
▪ Most abundant cell type. ▪ Mucosa of nonkeratinized stratified squamous epithelium and
▪ Ciliated cells. includes the palatine and lingual tonsils.
o Goblet cells o Laryngopharynx
▪ Numerous cells that secrete mucin. ▪ Short, narrow region caudal to the oropharynx and continues
o Brush cells at its inferior end with both the larynx and esophagus.
▪ Columnar cells that bear sparse, blunt microvilli. ▪ Lined with of nonkeratinized stratified squamous epithelium.
▪ Chemosensory receptors resembling gustatory cells. Larynx
o Small granule cells (Kulchitsky cells) • Short passageway for air between the pharynx and the trachea.
1 | The Respiratory System
, Junqueira’s Basic Histology Text and Atlas, 16th Edition
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
• Walls are reinforced with hyaline cartilage (thyroid, cricoid, and the inferior • Trachea divides into two primary bronchi that enter each lung hilum along with
arytenoid) and smaller elastic cartilages (epiglottis, cuneiform, corniculate, and lymphatic and blood vessels.
superior arytenoid). • Three secondary (lobar) bronchi in the right lung and two in the left lung, supplying
• Maintains an open airway and participate in phonation. each pulmonary lobe.
• Epiglottis • Secondary bronchi again divide, forming the tertiary (segmental) bronchi. Tertiary
o Flattened structure projecting from the upper rim of the larynx. bronchi and its smaller branches constitute a bronchopulmonary segment. These
o Prevent swallowed food or fluid from entering the air tubes. segments are import in surgical resection of diseased lung tissue without affection
o Lingual surface is lined with stratified epithelium while the laryngeal nearby healthy tissue.
surface undergoes transition to respiratory epithelium at variable points. • The terminal branches of the smaller bronchi are called bronchioles and each enters
o Mixed serous and mucous glands are present in the lamina propria. a pulmonary lobule, where it branches to form five to seven terminal bronchioles.
• Two pairs of folds separated by a narrow space or ventricle are seen below the • Histological organization of the epithelium and lamina propria of the smaller
epiglottis and laryngeal vestibule. bronchi and bronchioles gradually becomes more simplified.
o Vestibular folds Bronchi
▪ Upper pair of folds and are immovable. • Mucosa of larger bronchi is structurally similar to the tracheal mucosa except for
▪ Partly covered with respiratory epithelium. the organization of cartilage and smooth muscle.
o Vocal folds (cords) • The lumen of primary bronchi is completely encircled by cartilage rings. As the
▪ Lower pair of folds and are movable important for phonation. bronchial diameter decreases cartilage rings are gradually replaced with smaller
▪ Lined with nonkeratinized stratified squamous epithelium that isolated plates of hyaline cartilage.
protects the mucosa from abrasion and desiccation. • Lamina propria is abundant in small mucous and serous glands, and crisscrossing
▪ Vocal ligament, a dense regular bundle of elastic CT, supports bundles of spirally arranged smooth muscle and elastic fibers.
the free flaps of each vocal fold. • Contraction of this muscle layer is responsible for the mucosal folds evident in the
▪ Vocalis muscle are present in the deep mucosa that allow each bronchial mucosa.
vocal fold to be moved. Bronchioles
▪ During phonation, the vocalis muscle adducts the vocal folds • Intralobular airways with diameters of 1 mm or less formed after the tenth
together and the rima glottidis, opening between the vocal generation of branching.
folds, narrows and causes the vocal folds to vibrate.
• Lack mucosal glands and cartilage supports but reinforced with dense CT
▪ Sound qualities are altered by the changing the tension on the
associated with the smooth muscle.
vocal folds, width of the rima glottidis, and the volume of air
• Larger bronchioles are lined with respiratory epithelium with decreased height and
expelled.
complexity becoming ciliated simple columnar or simple cuboidal epithelium in
Trachea
the smallest terminal bronchioles.
• A 10-12 cm long air tube lined with respiratory mucosa.
• The ciliated epithelial lining of the bronchioles begins the mucociliary apparatus
• Lamina propria contains numerous seromucous glands that produce watery mucus.
important in clearing debris and mucus.
• Walls are reinforced with C-shaped rings of hyaline cartilage between the • The cuboidal epithelium of terminal bronchioles consists:
submucosa and adventitia to keep the tracheal lumen open. o Largely of club cells (bronchiolar exocrine cells or previously called the
• Open ends of the cartilage are on the posterior side where the esophagus is situated. Clara cells) with various functions, such as:
This area is bridged by a smooth muscle bundle, the trachealis muscle. ▪ Secretion of surfactant lipoproteins and mucins.
• Trachealis muscle relaxes during swallowing allowing the esophagus to bulge into ▪ Detoxification
the lumen of the trachea. ▪ Secretion of antimicrobial peptides and cytokines.
• This muscle strongly contracts during cough reflex to narrow the tracheal lumen o Chemosensory brush cells
and provide increased velocity of the expelled air. o DNES small granule cells
Bronchial Tree and Lung o Small population of stem cells
Respiratory Bronchioles
2 | The Respiratory System
