The respiratory system is divided into (a) conducting and (b) respiratory portions. The conducting part consists of passageways which carry air to the respiratory portion. The respiratory portion begins at the level where alveoli first appear in the final branches of the bronchioles. Respiration (gaseous exchange between blood and air) occurs across the walls of the alveoli. The conducting portion includes parts which are outside the lung or extrapulmonary (nasal cavities, nasal pharynx, larynx, trachea and primary bronchi), and those which are inside the lung or intrapulmonary (rest of the bronchi and bronchioles). All of the respiratory portion is intrapulmonary and consists of the respiratory bronchioles, alveolar ducts, and alveoli).
A. Nasal Cavity
The epithelial lining at the entrance (vestibule) to the nasal cavity exhibits a gradual change from keratinized stratified squamous epithelium of the skin in the nasal vestibule to the pseudostratified columnar ciliated epithelium that is characteristic of the nasal mucosa posterior to the vestibule and much of the rest of the respiratory system. Therefore, the epithelium is called respiratory epithelium.
The mucosal surface of the rest of the conducting portion is lined by respiratory epithelium, except the true vocal fold (vocal cord or vocal ligament) in the larynx, which is lined by a stratified (sometimes keratinized) squamous epithelium. The upper false vocal fold (vestibular or ventricular fold) is covered by respiratory epithelium, which makes an abrupt transition to a stratified squamous epithelium over the true vocal fold. The stratified epithelium serves to protect the vocal cords from abrasion caused by vibrations of the true vocal folds during phonation.
The trachea bifurcates into two primary bronchi, which enter the lung and then branch several times to give rise to smaller secondary and tertiary bronchi. Bronchi differ from the trachea in having plates rather than rings of cartilage, and in having a layer of smooth muscle between the lamina propria and submucosa. In smaller branches, the amount of cartilage decreases, whereas the amount of smooth muscle increases. Also, the number of glands and goblet cells decreases.
The respiratory system is divided into (a) conducting and (b) respiratory portions. The conducting part consists of passageways which carry air to the respiratory portion. The respiratory portion begins at the level where alveoli first appear in the final branches of the bronchioles. Respiration (gaseous exchange between blood and air) occurs across the walls of the alveoli. The conducting portion includes parts which are outside the lung or extrapulmonary (nasal cavities, nasal pharynx, larynx, trachea and primary bronchi), and those which are inside the lung or intrapulmonary (rest of the bronchi and bronchioles). All of the respiratory portion is intrapulmonary and consists of the respiratory bronchioles, alveolar ducts, and alveoli).
A. Nasal Cavity
The epithelial lining at the entrance (vestibule) to the nasal cavity exhibits a gradual change from keratinized stratified squamous epithelium of the skin in the nasal vestibule to the pseudostratified columnar ciliated epithelium that is characteristic of the nasal mucosa posterior to the vestibule and much of the rest of the respiratory system. Therefore, the epithelium is called respiratory epithelium.
B. Larynx
The mucosal surface of the rest of the conducting portion is lined by respiratory epithelium, except the true vocal fold (vocal cord or vocal ligament) in the larynx, which is lined by a stratified (sometimes keratinized) squamous epithelium. The upper false vocal fold (vestibular or ventricular fold) is covered by respiratory epithelium, which makes an abrupt transition to a stratified squamous epithelium over the true vocal fold. The stratified epithelium serves to protect the vocal cords from abrasion caused by vibrations of the true vocal folds during phonation.
C. Bronchi
The trachea bifurcates into two primary bronchi, which enter the lung and then branch several times to give rise to smaller secondary and tertiary bronchi. Bronchi differ from the trachea in having plates rather than rings of cartilage, and in having a layer of smooth muscle between the lamina propria and submucosa. In smaller branches, the amount of cartilage decreases, whereas the amount of smooth muscle increases. Also, the number of glands and goblet cells decreases.
reference:
https://histology.medicine.umich.edu/resources/respiratory-system