The respiratory system consists of conducting and respiratory portions. The conducting portion includes the nasal cavities, pharynx, larynx, trachea, and bronchi. It contains cartilage and pseudostratified ciliated columnar epithelium. The respiratory portion includes bronchioles, alveolar ducts, alveolar sacs, and alveoli. It lacks cartilage and contains simple cuboidal epithelium with Type I and II pneumocytes for gas exchange. The alveoli are surrounded by a highly vascularized connective tissue layer and are the primary sites of oxygen/carbon dioxide exchange.

1. 


2. RESPIRATORY SYSTEM
 CONDUCTING
PORTION
 RESPIRATORY
PORTION

3. SKELETAL MUSCLES AND BONES ARE REQUIRED
FOR RESPIRATORY SYSTEM FUNCTION
RIBS
STERNUM
INTERCOSTAL MUSCLES
DIAPHRAGM

4. GENERAL ORGANIZATIONAL PATTERN
OF CONDUCTING PORTION
OF RESPIRATORY SYSTEM
 MUCOSA
Luminal sheet epithelium
(typically “respiratory epithelium”)
Lamina propria (loose FECT)
 SUBMUCOSA (mod. dense FECT)
(not always present or merged
with lamina propria, serous or mixed glands may
be present in the lamina propria or submucosa)
 “MUSCULARIS” EXTERNA (may be smooth
muscle, cartilage, or bone)
 ADVENTITIA or SEROSA (absent in nasal cavity)

5. CELL TYPES FOUND IN
“RESPIRATORY EPITHELIUM”
PREDOMINANT CELL TYPES
 Ciliated columnar cells – move
mucus
 Goblet cells – secrete mucus
 Basal cells – replace damaged cells
LESS COMMON CELL TYPES
 Brush cells – sensory receptor cells
 Dense core granule cells (Small granule
cells) – enteroendocrine cells
 Clara cells (trachea and bronchi) – protein
secreting cells, secrete surfactant

6. PREDOMINANT CELL TYPES
FOUND IN “RESPIRATORY EPITHELIUM”
Ciliated columnar cell Goblet cell (Mucous cell)
Basal cell
Source: Lentz. 1971. Cell Fine Structure.

7. “RESPIRATORY EPITHELIUM”
Ciliated cells
Goblet cell/ Brush
Mucous cell cells
Basal cell Small granule cell
Source: Weiss. 1983. Histology. Cell and Tissue Biology. 5th Edition.

8. (surfactant)

9. “RESPIRATORY” EPITHELIUM
Ciliated cells
Goblet cells Cilia
Small
Basement membrane
granule
Basal cell cell

10. EPITHELIA OF REGIONS WITHIN
NASAL CAVITIES
 VESTIBULE or
OLFACTORY
NOSTRIL SEGMENT
Stratified squamous
sheet epithelium
RESPIRATORY
SEGMENT
 RESPIRATORY
SEGMENT
”Respiratory NOSTRIL
epithelium”
 OLFACTORY
SEGMENT
Olfactory
epithelium

11. NASAL CAVITIES/ NASAL PASSAGEWAYS
OEp = olfactory
epithelium
OM = olfactory
mucosa
Rep = “respiratory
epithelium”
EB = bone
Source: Plate 88, Figure 1 in Ross et al. 1995. Histology. A Text and Atlas. 3rd Edition.

12. CELL TYPES FOUND IN
OLFACTORY EPITHELIUM
 Sustentacular or
supporting cells
 Olfactory cells
 Basal cells
 Brush cells

13. Mucosa of the Olfactory Segment
of the Nasal Cavity

14. Mucosa of the Olfactory Segment
of the Nasal Cavity
SC = supportive
cells
OC = olfactory
neuron cell bodies
BC = basal cells
BG = olfactory
glands (serous)
N = peripheral
nerves
V = blood vessels
C = capillaries
Source: Plate 88, Figure 2 in Ross et al. 1995. Histology. A Text and Atlas. 3rd Edition.

15. NASAL CAVITIES/NASAL PASSAGEWAYS
are separated from oral cavity by PALATE
OLFACTORY
SEGMENT
RESPIRATORY
SEGMENT
NOSTRIL
HARD PALATE SOFT PALATE
Modified from: Figure 18.1 in Ross et al. 1995. Histology. A Text and Atlas. 3rd Edition.

16. SOFT PALATE
NASAL
ORAL CAVITY
CAVITY side
side
“Respiratory epithelium”
of Nasal Mucosa
Source: Hammersen. 1980. Histology.

17. PHARYNX
”Respiratory
epithelium”
Stratified squamous
sheet epithelium
Modified from: Figure 18.1 in Ross et al. 2003. Histology. A Text and Atlas. 4th Edition.

18. RESPIRATORY SYSTEM
 NASAL CAVITIES/
NASAL PASSAGEWAYS
 PHARYNX -
nasopharynx, oropharynx
 LARYNX
 TRACHEA
 EXTRAPULMONARY
BRONCHI
 LUNGS

19. LARYNX and TRACHEA
bone
cartilage
Food
cartilage
cartilage
Surface View Mid-longitudinal Section
Source: Leeson & Leeson. 1981. Histology. 4th Edition.

20. EPIGLOTTIS of LARYNX
Stratified squamous
epithelium
Elastic Cartilage
Stratified squamous
or pseudostratified
columnar epithelium
Source: Hammersen. 1980. Histology. A Color Atlas of Cytology, Histology and Microscopic Anatomy. 2nd Edition.

21. LARYNX
Epiglottis
Stratified squamous
sheet epithelium
Ventricular fold/
false vocal cord
Vocal fold/
true vocal cord
Pseudostratified ciliated
columnar sheet epithelium
Source: Hammersen. 1980. Histology. A Color Atlas of Cytology, Histology and Microscopic Anatomy. 2nd Edition.

22. LARYNX
Epiglottis
Cartilaginous plate in
“Muscularis” Externa
Intrinsic glands in
Lamina propria of
Striated skeletal Mucosa
muscle tissue in
“Muscularis” Externa
Vocal ligament
Vocalis muscle
Cartilaginous plate in
“Muscularis” Externa
Source: Hammersen. 1980. Histology. A Color Atlas of Cytology, Histology and Microscopic Anatomy. 2nd Edition.

24. RESPIRATORY SYSTEM
 NASAL CAVITIES/
NASAL PASSAGEWAYS
 PHARYNX -
nasopharynx, oropharynx
 LARYNX
 TRACHEA
 EXTRAPULMONARY
BRONCHI
 LUNGS

25. Trachea
 Mucosa
“Respiratory” epithelium (+/- Clara cells)
Lamina propria of loose FECT
 Submucosa
Loose to moderately denseFECT,
denser than lamina propria,
may contain compound tubuloacinar glands
 “Muscularis”externa
Hyaline cartilages (horseshoe-shaped “rings”)
Smooth muscle across open ends of cartilages
Moderately dense FECT connects adjacent rings
 Adventitia
Loose FECT

26. TRACHEA
Adventitia “Muscularis”
Externa
luminal
epithelium
in submucosa
Mucosa
(trachealis muscle)
Source: Leeson & Leeson. 1981. Histology. 4th Edition.

28. TRACHEA

29. TRACHEA

30. LUMINAL EPITHELIUM OF TRACHEA
(“Respiratory” Epithelium)
Ciliated cells
Goblet cells Cilia
Small
Basement membrane
granule
Basal cell cell

31. RESPIRATORY SYSTEM
 NASAL CAVITIES/
NASAL PASSAGEWAYS
 PHARYNX -
nasopharynx, oropharynx
 LARYNX
 TRACHEA
 EXTRAPULMONARY
BRONCHI
 LUNGS

32. Bronchus (very similar to Trachea)
 Mucosa
“Respiratory” epithelium (+/- Clara cells)
Lamina propria of loose FECT
 Submucosa
Loose to moderately denseFECT,
denser than lamina propria,
may contain compound tubuloacinar glands
 “Muscularis”externa
Hyaline cartilages (horseshoe-shaped “rings”)
Smooth muscle across open ends of cartilages
Moderately dense FECT connects adjacent rings
 Adventitia
Loose FECT

34. RESPIRATORY SYSTEM
PULMONARY LOBULE
Source: Leeson & Leeson. 1981. Histology. 4th Edition.

35. ORGANIZATION OF LUNG
3-9 = intrapulmonary bronchi
10 = large bronchiole
tb = terminal bronchiole
rb = respiratory bronchiole
ad = alveolar duct
as = alveolar sac
a = alveolus
l = lobule
PULMONARY LOBULE
Source: Leeson & Leeson. 1981. Histology. 4th Edition.

36. HISTOLOGICAL FEATURES
OF PULMONARY COMPONENTS

37. ORGANIZATION
OF LUNG
Source: Gartner & Hiatt. 1994.
Color Atlas of Histology. 2nd Edition.

38. ORGANIZATION OF LUNG
alveoli
Source: Freeman & Bracegirdle. 1976. An Advanced Atlas of Histology.

39. ORGANIZATION OF LUNG
3-9 = intrapulmonary bronchi
PULMONARY LOBULE
Source: Leeson & Leeson. 1981. Histology. 4th Edition.

40. Intrapulmonary Bronchi
 Mucosa
“Respiratory” epithelium (+/- Clara cells)
Lamina propria of loose FECT
 “Muscularis”
Spiral bundles of smooth muscle
 Submucosa
Loose to occasionally moderately dense FECT,
may contain compound tubuloacinar glands
 “Muscularis”externa
Hyaline cartilages (horseshoe-shaped “rings”)
Smooth muscle across open ends of cartilages
Moderately dense FECT connects adjacent rings
 Adventitia
Loose FECT

41. INTRAPULMONARY BRONCHUS
Mucosa
Bronchiole
branching off
of bronchus Intrinsic glands in
Lamina Propria
FECT
Cartilaginous plate in
“Muscularis” Externa
Source: Jungueira et al. 1975. Basic Histology. 4th Edition.

42. An Intrapulmonary Bronchus
Loose FECT
Pseudostratified Columnar Epithelium
Hyaline Cartilage
Smooth Muscle

43. BRONCHIOLES
<1 mm in diameter
No cartilage in wall
 MUCOSA
Luminal sheet epithelium
(ranges from pseudostratified
ciliated columnar in large
bronchioles to simple
cuboidal with mixed ciliated
and Clara cells in terminal
bronchioles)
Lamina propria = loose FECT
“MUSCULARIS” = bundles of
PULMONARY LOBULE smooth muscle
Source: Leeson & Leeson. 1981. Histology. 4th Edition.

44. TYPES OF BRONCHIOLES
 LARGE BRONCHIOLES
Pseudostratified ciliated columnar
sheet epithelium to simple columnar
sheet epithelium
 TERMINAL BRONCHIOLES
Mainly simple cuboidal sheet
epithelium
 RESPIRATORY BRONCHIOLES
Simple cuboidal sheet epithelium
(mainly Clara cells)
10 = large bronchiole
tb = terminal bronchiole
rb = respiratory bronchiole Source: Leeson & Leeson. 1981. Histology. 4th Edition.

45. CELL TYPES FOUND IN
LUMINAL EPITHELIUM OF BRONCHIOLES
Ciliated cell Clara cell Ciliated cell
 Ciliated cells
 Basal cells
 Goblet cells
 Brush cells
 Small granule cells
 Clara cells
Source: Ross et al. 1995. Histology. A Text and Atlas. 3rd Edition.

46. BRONCHIOLE
Source: Burkitt et al. 1993. Wheater’s Functional Histology. A Text and Colour Atlas.

47. Alveoli are where
the action is (at
least in terms of
gas exchange)

48. ORGANIZATION OF LUNG
alveoli
Source: Freeman & Bracegirdle. 1976. An Advanced Atlas of Histology.

49. ALVEOLI or AIR SPACES
AS = alveolar sac
A = alveolus

50. ALVEOLI (AIR SPACES)
Occur in the walls of
 Respiratory bronchioles
 Alveolar ducts
 Alveolar sacs
CONSIST OF:
 Alveolar Epithelium
 Thin region of
highly vascularized FECT
ad = alveolar duct
as = alveolar sac
a = alveolus Source: Leeson & Leeson. 1981. Histology. 4th Edition.

51. CELL TYPES FOUND IN
ALVEOLAR EPITHELIUM
Type I Pneumocytes [gas exchange]
Type II Pneumocytes [secrete
surfactant (mix of proteins and lipids)]
Brush Cells [sensory receptors]
Pulmonary Macrophages
[phagocytosis]

52. CELL TYPES FOUND IN
ALVEOLAR EPITHELIUM
(as observed at TEM level)
Type I Pneumocyte Type II Pneumocyte
(and adjacent capillary)
Source: Lentz. 1971. Cell Fine Structure.

53. Alveolar Wall Structure – Type I Cells

54. Lung Injected to Show Capillaries
Capillaries (red structures)
Alveoli

55. ALVEOLI ARE SITES AIR
OF GAS EXCHANGE
BLOOD
BLOOD
RBC

56. Alveolar Wall
Structure –
Type II or
Great Alveolar
Cells

57. CELL TYPES
FOUND IN
ALVEOLI
(as observed at the LM level)
In addition to Type I and Type
II alveolar cells
(pneumocytes), macrophages
are frequently observed
migrating along the alveolar
surface. Macrophages are
frequently detached from the
surface during processing.

58. Criteria for Classifying Intrapulmonary Structures
Structure Lining Epithelium Other Features
Bronchi pseudostratified hyaline cartilage in wall
columnar usually + smooth muscle
Bronchioles pseudostratified no hyaline cartilage in wall
columnar to smooth muscle present
simple cuboidal,
no squamous
Respiratory >50% cuboidal or little or no smooth muscle,
Bronchioles columnar, <50% usually some loose FECT
squamous (but
squamous present)
Alveolar Ducts <50% cuboidal, no smooth muscle, loose
Alveolar Sacs >50% squamous FECT sparse or absent

59. ALVEOLI & BRONCHIOLES
TB = terminal bronchiole
RB = respiratory bronchiole
AD = alveolar duct
AS = alveolar sac