Respiratory System
Medical Cell and Tissue Biology
Dr. Cathleen Pettepher
March 18, 2002
Larynx
 Framework of hyaline & elastic cartilages
– False vocal folds
– Ventricles
– Vocal folds:
• glottis
– Vocalis muscle
Vocal Folds
– two mucosal folds
– stratified squamous epithelium
– protects the mucosa from abrasion caused by the rapidly moving airstream
Contains:
– a supporting ligament
– vocalis muscle
(VL)
• generates tension in vocal fold
Larynx
 Remainder of the larynx is lined with ciliated, pseudostratified columnar epithelium
 CT contains:
– mixed mucoserous glands
Laryngeal Glands
 Secrete via ducts onto the surface
 along rim of aryepiglottic folds & ventricular folds
 absent from vocal ligaments, reappear toward base of vocal fold
Trachea
 Hollow, flexible tube
– Begins at larynx
– Ends at carina
 Bifurcates to form 1º bronchus for each lung
 reinforced by a skeleton of cartilage
 Consists of 4 layers
– Mucosa
– Submucosa
– Cartilaginous layer
– Adventitia
 Trachealis muscle - bridges gap between ends of cartilage
– smooth muscle
Tracheal Mucosa
 Secretory mucosa
– contains exocrine glands
 Pseudostratified columnar epithelium
– ciliated cells & mucous cells predominating
– other cell types present but poorly resolved with LM
 Varies in appearance
– sensitive to irritation
– responds by increasing in height
• mucous cells and glands undergo hypertrophy
– with prolonged irritation
• portions of epithelium may become stratified squamous epithelium
• termed squamous metaplasia
Tracheal Epithelium
 5 different cell types present in the epithelial layer
 high levels of activity for mitochondrial and lysosomal enzymes
– associated with oxidative phosphorylation
– attributed to ciliated and mucous cells
Ciliated Cells
 Mitochondria:
– concentrated just beneath the basal bodies in the apical cytoplasm
 contain cilia and microvilli
– ~300 cilia per cell
Mucous Cells
 Exhibit characteristics of protein-secreting cells:
– extensive ER in basal region of cell
– supranuclear Golgi apparatus
– coalescing mucous droplets in apical cytoplasma
Basal Cells
 Non-ciliated epithelial cells
 Nuclei form a row close to the basal lamina
 These cells do not extend to the free surface
 Function as a reserve population for the epithelium
Brush Cells
 Non-ciliated cells
 contain long, straight microvilli
 Some form epithelio-dendritic (afferent) synapses with nerve processes in CT
 May possess glycogen granules and a lot of sER
Small Granular Cells
 Rare cells
– Kulchitsky cells (K)
– solitary & sparsely dispersed
 Characterized by small dense-core granules
 APUD cell
– they take up amine precursors & store them in granules
Epithelial Renewal
 All epithelial elements are joined to each other on the sides by desmosomes and if they reach
the surface, by junctional complexes
 After trauma, neighboring mucous & basal (short) cells migrate to cover the denuded area
– They lose their distinguishing characteristics
– They divide and form a population of immature cells
– these in turn divide and redifferentiate into mucous and ciliated cells
Lamina Propria
 Loose CT containing:
– interwoven collagenous & elastic fibers
– many vascular channels
– fixed & wandering CT cells
 Elastic fibers:
– run in a predominantly longitudinal direction
– interconnected by slender fibrils
– peripherally these fibrils condense into an elastic membrane demarcating the lamina
propria from the submucosa
Submucosa
 fewer elastic fibers and more collagen fibers
 fibers run in bundles among the seromucous glands
 blends into peri-chondrium of the cartilages
Intrapulmonary Bronchi
 Mucosa
 Muscularis
– continuous layer of smooth muscle that maintains appropriate diameter of airway
 Submucosa
 Cartilaginous layer:
– discontinuous plates
– become fewer in #
 Adventitia
Bronchioles (1 mm or less)
 Bronchopulmonary segments are further divided into pulmonary lobules with each lobule
supplied by a bronchiole
 delicate CT septa separate adjacent lobules
 pulmonary acini are smaller units of structure that make up each lobule
 Respiratory bronchiolar unit:
– smallest functional unit of pulmonary structure
– consists of single respiratory bronchiole and the alveoli that is supplies
 these branch > smaller terminal bronchioles
– final segments of conducting portion of respiratory system
 these branch >> respiratory bronchioles
– contain alveoli
– 1st respiratory unit of lung
 Epithelium gradually transforms to simple ciliated columnar epithelium
– goblet cells present
 no submucosal glands present
 cartilaginous plates are replaced with a thick layer of smooth muscle
Terminal Bronchioles
 Simple cuboidal epithelium
– contains Clara cells that are found among the ciliated cells
– occasional brush cells and dense core granular cells are present
 Circumferential layer of smooth muscle
Clara Cells
 Non-ciliated cells with dome-shaped apical surface
 Secretory granules
– Secrete a surface-active lipoprotein
– prevents luminal adhesion should the wall of the airway fold on itself -- especially during
expiration
Respiratory Bronchioles
 Transitional zone
– concerned with both air conduction & gas exchange
 Cuboidal epithelium:
– Clara & ciliated cells
 Alveoli
– thin-walled outpocketings
– sites where gas exchange occurs
Alveolar Ducts and Sacs
 Alveolar ducts:
– elongated airways with few walls
– alveoli act as their peripheral boundary
 Alveolar sacs:
– surrounded by clusters of alveoli which open up into these spaces
Terminal Air Spaces -- Alveoli
 Actual site of gas exchange between air and blood
 100 million alveoli per lung
 thin-walled polyhedral chambers
 rings of smooth muscle in knob-like intra-alveolar septum
Alveolar Epithelium
 Simple squamous epithelium
 composed of 3 cell types:
–
–
–
Alveolar type I cells
Alveolar type II cells
Brush cells
Alveolar Macrophages
 dust cells
– function both in CT of the septum and in the air spaces
– scavenge the surface to remove inhaled particulate matter
– also phagocytize red blood cells that may enter the alveoli in heart failur -- heart failure
cells
Alveolar Type I cells
 Pneumocytes
 extremely thin squamous cells
 line 95% of the alveolar surface
 deficient in most organelles
 joined to one another and other cells by zona occludens
Alveolar Type II Cells
 Secretory (exocrine) cells
 Cuboidal cells that bulge into air space
 granules that contain stacks of parallel membrane lamella
 rich in phospholipids -surfactant
 forms a mono-molecular layer that reduces surface tension
Alveolar Septum
 alveolar epithelial cells
 basal lamina of epithelial cells often fused with basal lamina of capillary endothelial cell
 endothelial cells
 Thin portion contains:
– surfactant
– Type I pneumocytes
– basal lamina -- basal lamina
– capillary endothelial cell
 Thick portion may contain CT cells & fibers --fluid can accumulate