The document provides details on the structure and function of various parts of the respiratory system. 1) The nasal cavity contains respiratory epithelium lined with ciliated cells and goblet cells that secrete mucus to trap particles. It also contains olfactory epithelium specialized for smell. 2) The pharynx and larynx contain pseudostratified ciliated epithelium for breathing and stratified squamous epithelium to protect from abrasion during swallowing and coughing. The vocal cords contain skeletal muscle to modulate voice. 3) The trachea and bronchi contain ciliated respiratory epithelium, glands, cartilage, and smooth muscle. Their function is to conduct air to and from the

1. Respiratory System Study Guide
Samantha Blum

2. The Conducting Division
This division includes structures from
nasal cavity to terminal bronchioles.

3. The Nasal Cavity
• The nasal cavity lies between the ethmoid bone superiorly and the palate inferiorly, and is vertically
divided into two halves by the nasal septum. It functions to condition the air that passes into the
lungs, houses the olfactory epithelium, and acts as a resonant chamber to enhance speech.
• Most of the chamber is lined with a pseudostratified, ciliated epithelium with goblet cells, called
"respiratory epithelium" because it lines the conducting division of the respiratory system. Note that
"respiratory epithelium" does not actually carry out gas exchange.
• In this horizontal section through the nasal cavity, identify the cartilaginous nasal septum and the
turbinate bones (conchae) (1X). Examine the lining epithelium, identifying ciliated columnar cells and
goblet cells (40X). Note that the goblet cells are thinner, and therefore somewhat harder to identify, than
the ones in the digestive system.
• In the adult, the lamina propria normally contains large numbers of blood vessels and seromucous glands;
very few of these are present in this fetal specimen (1X, 10X).
• What is the function of the goblet cells and seromucous glands of the nasal cavity?
– Mucus secreted by them is helpful in trapping smaller foreign particles

4. Goblet cell

5. Olfactory Epithelium
• The roof of the nasal cavity and the superior turbinate bone (concha) are covered with an epithelium
specialized for olfaction. Olfactory epithelium is categorized as pseudostratified columnar
epithelium, without goblet cells (4X, 20X).
• Within the underlying lamina propria, identify venules, as well as the nerve fibers arising from the
olfactory cells in the epithelium (40X). These nerve fibers (fila olfactoria) conduct olfactory information to
the brain through holes (the cribriform plate) in the intervening (ethmoid) bone.
• Also identify the serous Bowman's glands (20X, 40X), and their ducts that penetrate to the surface of the
epithelium. These glands are unique to the olfactory epithelium. The fluid released by the Bowman's
glands serves to trap odor molecules, which are then detected by the membrane-bound odorant receptors
of the olfactory cells.

6. The Pharynx:
Oropharynx & Laryngopharynx
• Note that these structures differ from nasopharynx with respect to type of mucosa, in that they contain
non-keratinized stratified squamous epithelium (10X, 40X). Why?
– The stratified squamous epithelium protects against abrasive activities, like swallowing or coughing
• Identify the lamina propria, and note that it contains abundant elastic fibers, lymphatic tissue, and mucous
and serous glands (5X).
Lamina propria

7. The Pharynx:
Nasopharynx
• No slide available
• Here, the epithelium is pseudostratified
ciliated. Why not stratified squamous?
– Nasopharynx is used exclusively for breathing, so
it is lined with the usual respiratory
(pseudostratified ciliated) epithelium

8. The Soft Palate
• This structure (0.3X) separates oropharynx and nasopharynx (note that the orientation of slide E-43A in
the Virtual Microscope puts the oral cavity facing up).
• Note that the epithelium on the nasal surface (1X, 3X, 10X) is pseudostratified ciliated, while the
epithelium on the oral surface (10X) is stratified squamous. Why?
– The nasal surface is only exposed to air and therefore has respiratory epithelium
– The oral surface, on the other hand, is exposed to food/swallowing and needs a tougher stratified squamous epithelium
• What is the function of the skeletal muscle of the soft palate?
Epithelium of nasal surface Epithelium of oral surface

9. Nasal Surface of Palate

10. Oral Surface of Palate

11. The Larynx
• The larynx connects pharynx
with trachea, and contains the
vocal cords

12. The Larynx:
Mucosa
Epithelium.
• Note that most of the larynx is covered at its luminal
surface (40X) by pseudostratified ciliated columnar
epithelium with goblet cells. In the region of the true
vocal fold, however, the epithelium is stratified
squamous (4X, 40X). Why?
– Epithelium of true vocal cords protect the mucosa from frictional
forces during phonation
Lamina propria.
• Note that this layer is thick, and has abundant elastic Most of larynx Region of true vocal cord
fibers (4X, 10X).
• Identify tubuloacinar mucous, serous, and mixed
seromucous glands (1X, 4X, 10X, 10X).
• Identify lymph nodules (4X). Why would you expect
them to be present here?
– Protects against antigens and allergens arriving in the inhaled air

13. The Larynx:
Submucosa, Vocal Cords, Cartilage
Submucosa (No recognizable submucosa is present
here.)
Vocal folds.
• Examine the region deep to (i.e. external to) the
lamina propria of the vocal folds, and identify a
large muscle mass (4X), comprised of skeletal
muscle (20X, 20X). What is the function of this
muscle?
Cartilage.
• Identify the mass of cartilage (1X) deep to the
lamina propria within the epiglottis. Why is this
type of cartilage located here?
• Note that the oral surface of the epiglottis is
covered with stratified squamous epithelium
(20X), while the pharyngeal surface has a
covering of pseudostratified columnar
epithelium with goblet cells (20X). Why?
– Oral surface is exposed to food/swallowing, while
pharyngela surface is only exposed to air
Oral surface of epiglottis Pharyngeal surface of epiglottis

14. The Larynx:
Submucosa, Vocal Cords, Cartilage
Cartilage.
• Speculate on the reason for fat within the epiglottal cartilage (5X).
Cartilage in epiglottis is dark region Fat in the epiglottal cartilage

15. Pseudostratified Ciliated Columnar
Epithelium of Laryngeal Mucosa

16. Stratified Squamous Epithelium of
Laryngeal Mucosa (vocal cords)

17. The Trachea:
Mucosa
Epithelium.
• Note the typical respiratory tract
epithelium (10X; 10X); at this level
in the respiratory tree, it is
pseudostratified ciliated columnar
epithelium with goblet cells (40X;
40X).
• Examine the thick yellow line
subjacent to the epithelium; this
basal lamina (40X) is the thickest in
the body.
Lamina propria.
• Note the abundance of
lymphocytes (20X, 40X) and some
solitary lymph nodules (4X).
• Identify the longitudinal elastic
membrane (20X, 40X) in deep
lamina propria. This layer forms the
boundary between the mucosa and
submucosa.

18. The Trachea:
Submucosa & Adventitia
Submucosa.
• Identify mixed tubuloalveolar
glands (10X, 40X, 40X) in this
region; try to follow a duct (10X)
to the luminal surface.
• Note the high vascularity of the
submucosa (10X; 20X). What
"conditioning" function does this
vascularity provide?
– High vascularity helps HEAT the
inhaled air
Adventitia.
• Horseshoe-shaped, incomplete
rings of tracheal cartilage (10X) lie
external to the submucosa.
Examine both longitudinal (4X)
and cross sections (4X) of trachea
to study these.
Longitudinal Cross-section

19. The Trachea:
Submucosa & Adventitia
• Examine the area of
posterior tracheal wall
lacking cartilage (cross
section); note that
bundles of smooth
muscle (trachealis
muscle, 4X, 5X; 40X)
connect the ends of the
cartilage.
• Examine the area
between two adjacent
cartilages (4X) (cross-
section).

20. The Lungs
DIVISION REGION SUPPORT GLANDS EPITHELIUM CELL TYPES ADDITIONAL FEATURES
sebaceous and sweat stratified squamous
nasal vestibule hyaline cartilage epidermis vibrissae
glands keratinized
hyaline cartilage and basal, goblet, ciliated,
nasal cavity: respiratory seromucous glands respiratory erectile-like tissue
bone brush, serous, DNES
Bowman's glands olfactory, sustentacular,
nasal cavity: olfactory bone olfactory olfactory vesicle
(serous) basal
Extrapulmonary
basal, goblet, ciliated, pharyngeal tonsils,
conducting nasopharynx skeletal muscle seromucous glands respiratory
brush, serous, DNES eustachian tubes
respiratory and
hyaline and elastic mucouse and basal, goblet, ciliated, epiglottis, vocal folds,
larynx stratified squamous
cartilages seromucous glands brush, serous, DNES vestibular folds
nonkeratinized
trachea and primary hyaline cartilage and mucous and basal, goblet, ciliated, C-rings and trachealis
respiratory
bronchi dense irregular C.T. seromucous glands brush, serous, DNES s.m. in adventitia
plates of hyaline
secondary
hyaline cartilage and basal, goblet, ciliated, cartilage and two
(intrapulmonary) seromucous glands respiratory
smooth muscle brush, serous, DNES ribbons of helically
bronchi
oriented s.m.
less than 1mm in
Intrapulmonary simple columnar to ciliated cells and Clara diameter; supply air to
primary bronchioles smooth muscle NO glands
conducting simple cuboidal cells lobules; two ribbons of
helically oriented s.m.
less than 0.5mm in
some ciliated cells and
diameter; supply air to
terminal bronchioles smooth muscle NO glands simple cuboidal many Clara cells (no
lung acini; some smooth
goblet cells)
muscle
alveoli in their walls;
ciliated cuboidal cells,
some smooth muscle simple cuboidal and alveoli have smooth
respiratory bronchioles No glands Clara cells, Types I and II
and collagen fibers simple squamous muscle sphincters in
pneumocytes
their opening
Type III collagen no walls of their own,
Types I and II
alveolar ducts (reticular) fibers; s.m. NO glands simple squamous only a linear sequence
Respiratory pneumocytes
sphincters of alveoli of alveoli
Type III collagen and Types I and II
alveolar sacs NO glands simple squamous clusters of alveoli
elastic fibers pneumocytes
200 microns in
Type III collagen and Types I and II

21. Bronchi
• Extrapulmonary (primary) bronchi.
These branches of the conducting
division resemble the trachea, but
have a smaller diameter.
• Intrapulmonary (secondary and
tertiary) bronchi. These branches
differ from extrapulmonary bronchi in
several ways:
– Examine several bronchi (small:
10X, 40X; medium: 4X, 40X, 100X; large:
4X, 40X), and note that mucosal
epithelium decreases in height, and in
frequency of goblet cells, as bronchi
decrease in size.
– Note that the epithelium (10X, 40X) of
the smallest bronchi is ciliated simple
columnar with goblet cells.
– Note the presence of many reticular and
elastic fibers (20X) in the lamina propria.

22. Bronchi
Intrapulmonary (secondary and tertiary) bronchi.
• These branches differ from extrapulmonary
bronchi in several ways:
• Identify the muscularis mucosa (10X, 40X), a
layer of interlacing smooth muscle bundles
that spiral around the bronchus between
mucosa and submucosa. Abundant elastic
fibers intermingle with muscle bundles here.
• Note that, as in trachea and extrapulmonary
bronchi, the loose C.T. submucosa contains
many mucous and mixed seromucous glands
(10X, 40X).
• Cartilage is present in bronchial adventitia as
irregular plates rather than C-shaped rings
(schematic). As a result, the cross-sectional
appearance is round, not D-shaped as in
trachea. Identify such plates
(4X, 4X, 10X, 10X) , and note that smaller
bronchi have progressively less cartilage.

23. Bronchioles:
Mucosa
• Tertiary bronchi branch into bronchioles
(20X), which are conducting passageways
embedded in little or no connective
tissue, and surrounded by (but not in direct
communication with) pulmonary alveoli.
• Mucosal epithelium. This varies from ciliated
simple columnar with a few goblet cells, to
ciliated cuboidal (100X) with no goblet cells
(in terminal bronchioles).
• Identify non-ciliated Clara cells, also known as
bronchiolar cells (schematic; 50X, 100X)
scattered in the epithelium. The number of
Clara cells increases as bronchiole diameter
decreases, such that terminal bronchioles
have more non-ciliated Clara cells than
ciliated cuboidal respiratory epithelial cells.
• Note that Clara cells (50X, 100X) bulge
prominently into the lumen (airway).
• Identify the muscularis mucosae
(10X, 20X, 40X, 40X). of spirally arranged
smooth muscle, which is prominent here

24. Bronchioles:
Submucosa & Adventitia
• Submucosa. Note that, in
bronchioles (10X, 20X), this
layer lacks seromucous and
mucous glands.
• Note that bronchioles
(10X, 20X) have no
cartilage.
• Adventitia. Note that this
layer is much less
prominent (10X, 20X) than
in larger branches of the
conducting division.

25. The Respiratory Division
The respiratory division comprises all
respiratory tree branches smaller than terminal
bronchioles (respiratory bronchioles, alveolar
ducts, alveoli). Gaseous exchange occurs
through alveoli located throughout this division.

26. Respiratory Bronchioles
• Identify a terminal bronchiole that leads into a respiratory bronchiole (10X). What important functional
characteristic distinguishes respiratory bronchioles from other types of bronchiole?
– Respiratory bronchioles have alveoli, while terminal bronchioles do not. (Respiratory bronchioles are involved in gas exchange; terminal
bronchioles are not.)
– Alveolar ducts do not have epithelial walls of their own, so they are seen as openings in the epithelial lining at the transition from terminal
bronchiole to respiratory bronchiole.
• Note how the mucosa changes as the airway size decreases: large respiratory bronchioles have cuboidal
epithelial cells with occasional cilia (100X), while the epithelium of smaller respiratory bronchioles
(100X, 100X) has no cilia and is low cuboidal to squamous.

27. Respiratory Bronchioles
• Note the absence of goblet cells. Why would mucus not be a good idea here?
– A mucus lining in the respiratory bronchioles would interfere with gas exchange. The air should already be filtered of foreign particles by the
time it arrives in the respiratory division.
• Note the presence of a prominent smooth muscle muscularis mucosae (20X) with many elastic fibers
(100X).

28. Alveolar Ducts
• Note that these ducts have walls interrupted by numerous alveoli and alveolar clusters (20X).
• Note the the muscularis mucosae here is reduced to drumstick-like knobs of smooth muscle (circled) at
sites where duct wall interruptions occur (20X, 50X).
• What type of epithelium is present here?
– Type I and II pneumocytes
– Type I: thin squamous cells that represent 95% of alveolar lining
– Type II: secrete surfactant

29. Alveolar Sacs & Alveoli
• Alveolar Septum: Gaseous exchange
occurs here, between the lumen of the
alveolus and pulmonary capillary blood.
– Mucosa
• The squamous epithelium in this region
is greatly attenuated (thinned).
• Identify Type I pulmonary epithelial
pneumocytes (100X, 100X) with
flattened nuclei, and cytoplasm so
attenuated that it is not visible by light
microscopy. The pulmonary epithelium
and the vascular endothelium are too
thin and close together to be
distinguishable by light microscopy; the
structure of the blood-air interface is
clearly seen by electron microscopy
(EM).
• Identify Type II pneumocytes, also called
Great cells (schematic;
100X, 100X, 100X) scattered among
pulmonary epithelial cells and bulging
into the alveolar lumen. What substance
do these cells produce?
– surfactant

30. Alveolar Sacs & Alveoli
• Alveolar septum:
– Pulmonary arteries
• Identify pulmonary capillaries within
the interalveolar septum
(100X, 100X).
• Identify the endothelial cells of these
capillaries (100X, 100X, 100X, 100X);
note that they have very attenuated
(thinned) cytoplasm. Why?
– A thin epithelium promotes more efficient
gas exchange
– Zona diffusa
• The tissue space within the septum is
comprised of reticular and elastic
fibers and fine collagenous fibers; it
lies between the basal laminae of the
pulmonary epithelium and the
endothelium.
• Look for alveolar phagocytes
(100X, macrophages) within the septa.

31. Type II Pneumocyte

32. Clinical Correlation
1. Tuberculosis (Pathology slide HD008).
Tuberculosis is a chronic, infectious disease
caused by the organism Mycobacterium
tuberculosis; the disease causes 6% of all
deaths worldwide. Within the
lung, macrophages internalize invading
mycobacteria; once inside the
macrophage, however, the organism inhibits
normal lysosomal function and continues to
replicate. The body mounts a huge
macrophage-based response that results in
the formation of large tubercles (0.3X, 1X);
these characteristic structures contain a
central area of necrotic tissue sourrounded by
large numbers of multinucleated giant cells
and other cells of the immune system (40X).

33. Clinical Correlation
2. Emphysema (Pathology slide HD068)
Emphysema is a disease characterized
by enlargement of airspaces distal to
the terminal bronchioles, and
destruction of their walls (septa).
Alveolar walls become thin and
eventually disappear. The fusion of
adjacent alveoli results in large
airspaces (overview, 5X); this reduces
the amount of surface area available
for gas exchange, causing shortness of
breath. Emphysema and cigarette
smoking are strongly associated, and
the most severe form of the disease
occurs in the heaviest smokers.

34. Clinical Correlation
3. Hyaline Membrane Disease
(Pathology slide HD069)
Hyaline membrane disease often
occurs in babies born before ca.
24 weeks gestation, which is the
point at which Type II
pneumocytes begin to produce
surfactant. The detergent-like
properties of surfactant reduce
the surface tension of lung
fluid, permitting expansion of the
lungs. Without surfactant, too
much force is required to open the
alveolar spaces, which instead
remain collapsed (overview, 10X).

35. Clinical Correlation
4. Squamous cell carcinoma (Pathology
slide HD073)
Squamous cell carcinomas of the lung
usually begin at the hilum of the
bronchial tree. The bronchial
epithelium, normally
pseudostratified, becomes squamous
and less organized (dysplasia).
Eventually, uncontrolled growth
results in large masses that push into
the parenchyma of the lung
(overview). In many cases, such
tumors show whorls of well-
differentiated squamous cells (10X).
About 90% of lung cancers occur in
smokers.