Functions of the
Chapter 17 • Cooperates with the cardiovascular
The Respiratory system in supplying oxygen to cells and
System removing CO2
• Warms, moistens and filters debris and
pathogens from inspired air
• Contains receptors for smell
• Produces sound
• Helps eliminate wastes
RESPIRATORY SYSTEM OVERVIEW
• The upper respiratory tract includes:
• the nose,
• the pharynx and
• associated structures (tonsils, sinuses,etc.)
• The lower respiratory tract includes:
• the larynx,
• the trachea
• the bronchi and
• the lungs which contain branches of bronchi that
ultimately end in alveoli.
Functional Divisions Transition from Conducting to
• Conducting Structures that conduct air into the Respiratory Portions of the RT
lungs and condition it before it enters the lungs:
• the nose, • The cells and tissues of the conducting
• the pharynx, portion of the RT gradually change such that
• the larynx, there is a decrease in:
• the trachea • goblet cells
• the bronchi, bronchioles and terminal bronchioles. • cartilage
• Respiratory Structures where gas exchange • ciliated cells
occurs: • height of cells
• the respiratory bronchioles,
• and an increase in:
• alveolar ducts,
• smooth muscle
• alveolar sacs
• alveoli. • elastic fibers.
Air Conditioning Respiratory Epithelium
• A major function of the conducting portion
• PSCCE gradually changes to:
of the RT is to condition the inspired air, i.e.,
to warm, moisten and filter it. • simple columnar ET, then
• Structures that carry out these functions • simple cuboidal ET in terminal
• vibrissae (specialized hairs) • which lacks goblet cells but retains
• The mucous, ciliated respiratory epithelium ciliated cells
• highly vascularized underlying CT
• simple squamous ET in alveoli
• nasal conchae (turbinates) within the nasal
The Respiratory Epithelium SEM of Surface of Respiratory Epithelium
PSCCE lines most of the respiratory tract
except the terminal branches of the
bronchioles, the alveoli and inferior portions of
The lamina propria contains serous glands The movement of these cilia propels mucus and
that contribute to moistening inspired air. trapped particles toward the pharynx.
Five Cell Types in the
Respiratory Epithelium Figure 24-02a
(in order of abundance)
• Ciliated columnar cells
• Goblet (mucous) cells
• Basal (stem) cells
• Brush cells
• sensory receptors with numerous microvilli
• Small granule cells
• endocrine - may act on caliber of bv or airway
Note: all cell types sit on the basement membrane
The Nasal Cavity Paranasal Sinuses and
• Consists of: Conchae
• the Vestibule
• the external portion of the nasal cavity
• contains external nares lined with
keratinized stratified squamous ET that
gradually changes into respiratory ET
• the Nasal Fossae,
• two convoluted openings within the skull
• whose lateral walls contain three nasal
Nasal Conchae Paranasal Sinuses
• Function to increase the surface area of • Air-filled chambers that occur in the
the respiratory epithelium for filtering, frontal, maxillary, ethmoid and sphenoid
warming and moistening inspired air. bones of the skull.
• The lamina propria under the RE • They are lined with a thinner RE that
contains large venous plexuses called contains few goblet cells.
swell bodies • They communicate with the nasal cavity
• that alternately become engorged with through small openings.
blood, shifting air flow to allow RE to • They function to lighten the skull and act
recover from desiccation as resonating chambers for the voice.
Upper Respiratory Tract The Larynx
The nasopharynx contains the openings into the Eustachian
tubes and pharyngeal tonsil. The oropharynx contains the The larynx is a box supported by 9 cartilages.
lingual and palatine tonsils.
Larynx, posterior view Larynx, sagittal section
The lingual surface of the epiglottis is covered
with stratified squamous ET which changes to
PSCCE at the base of the laryngeal surface.
The Vocal Cords
• Below the epiglottis, the mucosa forms
two pairs of folds that extend into the
lumen of the larynx:
• The upper pair are the ventricular folds
(false vocal cords) covered with RE.
• The lower pair are the true vocal cords
containing the elastic vocal ligaments
and vocalis muscles covered by
stratified squamous ET.
The Glottis, closed Laryngoscopic View
Intrinsic laryngeal muscles close the glottis during swallowing.
Larynx, human VF
l.s. x14 • Extends from the base of the larynx to the
point at which it bifurcates into the two
VM = vocalis muscle
primary bronchi (about 10 cm or 4 in).
VoF = vocal fold • It is lined in RE and contains 16-20 C-shaped
VF = vestibular fold
GL = mucous and
VM rings of hyaline cartilage in the lamina propria.
LC = laryngeal • These incomplete rings keep the tracheal
GL lumen open and allow changes in its
• A fibroelastic ligament (annular ligament) and
the trachealis muscle (smooth muscle) bridge
the open ends.
Trachea and Esophagus, cs Trachea and Esophagus, cs
The incomplete rings of cartilage permit expansion
of the esophagus into the trachea during swallowing.
The Thoracic Cavity
Mucous and glands
C-shaped hyaline cartilage
The Right lung is thicker, broader and shorter
and has 3 lobes separated by 2 fissures.
The L lung has 2 lobes separated by a single oblique fissure.
Trachea and Bronchi, anterior view
The Bronchial Tree
• After entering the lungs, the primary bronchi give
rise to 3 bronchi in the R lung and 2 in the L.
• These are the secondary (lobar) bronchi which
are characterized by 5-6 cartilagenous plates
around their circumference.
• The lobar bronchi divide repeatedly (about 12
times) giving rise to smaller bronchi with fewer
and smaller plates of cartilage in their walls.
• Tertiary (segmental) bronchi have 3 plates of
The right primary bronchus is shorter,
wider and more vertical than the left. Implications?
The Bronchial Tree
Each lobe receives its own secondary (lobar) This is a plastic cast of an adult
bronchus which branches multiple times. As long as bronchial tree.
cartilage is present, these branches are bronchi.
Bronchi and Bronchioles Bronchus, x.s.
Photomicrograph of a section of Lung
A Large Bronchus
Bronchi have cartilage in their walls,
bronchioles do not.
Bronchioles Bronchiole, x.s.
• The terminal branches of bronchi are x270
• Bronchioles lack cartilage and glands but
retain PSCCE that gradually changes to simple
ciliated columnar with few goblet cells and
finally to simple cuboidal epithelium.
• They are 1 mm or less in diameter and have
• Their lamina propria is composed largely of
smooth muscle and elastic fibers.
• Vagal (parasympathetic) stimulation causes
constriction and sympathetic stimulation
causes dilatation of the bronchioles. Sm LT
Terminal Bronchioles Bronchioles, x.s. RB
• Lack cartilage, x132
• Lined in ciliated simple columnar TB
epithelium without goblet cells,
• Accompanied by branches of the TB
• Branch to form 2 or more respiratory
• The epithelium of terminal
bronchioles contains nonciliated,
secretory Clara cells.
A Lung Lobule
Pulmonary lobules are pyramid-shaped with the
apex (containing a bronchiole) pointed toward the
hilum of the lung. Each bronchiole divides to form 5-
7 terminal bronchioles within the lobule.
Organization of a
Lung Lobule Respiratory Bronchioles
• Lined with ciliated cuboidal epithelial
and Clara cells,
• With underlying smooth muscle and
• Walls are interrupted by numerous
alveoli where gas exchange occurs.
• At the distal portions, alveoli become
more numerous and the cuboidal
epithelial cells lose their cilia.
• The walls of alveolar ducts consist of • Common areas for openings of a
alveoli with smooth muscle bundles in cluster of alveoli,
the lamina propria, • Supported by elastic and reticular
• Smooth muscle disappears at the distal fibers.
ends of alveolar ducts,
• Elastic and collagen fibers provide the
only support for the duct and its alveoli.
Diagram of Lung Tissue SEM of Alveoli
bundles in the
walls of alveolar
ducts appear as
Cell Types in Alveoli
• Sac-like evaginations of the respiratory
bronchioles, alveolar ducts and alveolar sacs;
• The terminal portions of the bronchial tree;
• Covered by the richest capillary network in the septum has
body. thin and
• Walls contain: thick
• Type I (squamous alveolar) cells, portions.
• Type II (great alveolar or septal) cells and
• macrophages (dust cells).
Type I (squamous alveolar) cells make up
• A few brush cells may be present to serve as 97% of the alveolar surface and
receptors monitoring air quality. Type II (septal or “great alveolar”) cells are
most of the remaining 3%.
Respiratory Membrane The Respiratory Membrane
(Blood-air Barrier or Alveolar-capillary Barrier)
The squamous Type I cells provide a barrier of air space
minimal thickness that is readily permeable to meets a
gases. The Type II cells secrete surfactant which
lowers alveolar surface tension preventing
collapse of alveoli.