The epithelium lining the respiratory tract from the nasal fossa through the bronchi is called the respiratory mucosa and is characterized by a pseudostratified ciliated epithelium with abundant non-ciliated cells known as goblet cells. - [Source: medcell.med.yale.edu/histology/respiratory_system_lab.php]

1. Respiratory System

2. Functions of the Respiratory System
 This “gas exchange” is the function of
the respiratory system.
All higher animals require a
mechanism to:
1.Obtain O2 from the environment
2.and get rid of CO2

3. Epithelium in the
respiratory system Olfactory
epithelium
Respiratory
epithelium Olfactory

4. Epithelium in the
respiratory system
Olfactory
Nose
Skin junction
Nasal cavity
Air sacs
Air sac
Respiratory
epithelium
Histo 36 Conducting
bronchiole

5. Conducting Portion
 Extrapulmonary
• Nasal cavities
• Pharynx
• Larynx
• Trachea
• Bronchi
 Intrapulmonary
• Intra. Bronchi, bronchioles, terminal
bronchioles

6. Respiratory
Portion
 Respiratory
bronchiole
 Alveolar sacs
 Alveolar ducts
 Alveoli

7. Extrapulmonary region
 Function: Humidifies, cleanses and
adjusts the temperature of inspired
air.
 Mucosa: PSEUDOSTRATIFIED
CILIATED COLUMNAR w/ GOBLET
CELLS (w/ seromucous glands)

8. Nasal Cavity
1. Cutaneous region
2. Respiratory region
3. Olfactory region

9. Cutaneous region
 aka nasal vestibule
 rostral: lined by a thick SSE
 midvestibule: thinner &
nonkeratinized
 caudal: stratified cuboidal
(transitional zone)

10. Respiratory region
 Epithelium lining the caudal 2/3 of the
nasal cavity proper
 Lining: respiratory epithelium
• Cells: ciliated, secretory, brush, basal
cells
• *The respiratory mucosa is more vascular
than other regions; cavernous stratum –
it is the highly vascular propria-
submucosa.

11. Olfactory region
 Dorsocaudal portion of the nasal
cavity.
 Lining: ciliated pseudostratified
columnar epithelium.
 Cell types: basal, sustentacular
olfactory cells
 Distinguished from respiratory mucosa: (1) thicker
epithelium, (2) numerous tubular glands, (3) bundles
of nonmyelinated nerve fibers in lamina propria.

12. Olfactory glands
 Characteristic feature;
branched
tubuloalveolar serous
glands – deliver
secretions to
olfactory surface.
 Function: secretion
serves as a trap and
solvent for
odoriferous
substances.

13. Olfactory epithelium
has no goblet cells.

14. Conditioning Air By The Conducting
Portion
Nasal fossae
– Superior conchae - olfactory
epithelium long cilia, nervous cells
– Middle conchae - respiratory
epithelium
– Inferior conchae - respiratory
epithelium
Swell bodies
– large venous plexus that direct air
(occludes air way)
– Allergic reaction or inflammation
restrict air flow
counter current system
warms air

15. Respiratory (Olfactory) mucosa and nasal septum
Bowman’s
glands
Highly vascular
lamina propria
Swell bodies
Olfactory
epithelium
Respiratory
epithelium

16. Respiratory (Olfactory) mucosa and nasal septum
Nerves
Highly vascular
lamina propria
Olfactory
epithelium
Bowman’s
glands
Nerve

17. Larynx
 Formed by irregularly shaped
plates of hyaline & elastic
cartilage.
 Lining: respiratory epithelium;
some – SSE – NK.
 Lumen: vestibule, ventricle,
infraglottic cavity

18. Hyaline cartilage provides flexible
support in the respiratory system
to hold the air way open.
Elastic cartilage in epiglottis
Hyaline cartilage

19. Larynx
Thyroid cartilage
Cricoid
cartilage
Tracheal cartilages
True vocal cords
The false
vocal
cords
Laryngeal
ventricle
Vocal cord muscles
Air space lumen

20. Larynx
Thyroid cartilage
Vocal cord
muscles
Respiratory
epithelium
Stratified
squamous
epithelium

21. Larynx
(lower portion)
Cricoid cartilage
Tracheal cartilage
Respiratory
epithelium
lining
Esophagus

22. Trachea
1. Mucosa
2. Submucosa
3. Cartilaginous layer
4. Adventitia

23. Trachea (Mucosa)
 Lining: respiratory epithelium
 Principal cell types: (1) ciliated,
(2) secretory, (3) basal
 Lamina propria, elastic lamina

24. Goblet cells –
readily seen after
they have
accumulated
mucinogen
granules in their
cytoplasm (EM of
human trachea).

25. Trachea (Submucosa)
 Serous & seromucous glands
 Tracheal glands – provide most of
the secretory material that covers
the ciliated surface in the trachea.

26. Trachea (Adventitia)
 Hyaline cartilage – most
distinctive feature; C- or U-shaped
stacked one on top of each other –
support.
 Trachealis muscle

27. Trachea (rat)
Principal features.
1.0 mm
Cartilage of trachea
Oesophagus
Muscle (skeletal)
Line across lumen is a fold in the section
DorsalVentral
Thyroid
Lumen
of trachea

28. Trachea (rat) Tracheal wall
1.0 mm
•Hyaline cartilage is present. It gives support during respiration and rigidity prevents collapse.
•Cartilage rings (incomplete): radial expansion possible; bolus of food can pass down the
esophagus.
cartilage
lumen

29. Trachea (rat) Tracheal wall
1.0 mm
Trachealis muscle at the dorsal aspect of the trachea.

30. Trachea (rat) Epithelial lining
25 µm
Pseudostratified, ciliated, columnar epithelium.
mucous on surfacecilia
pseudostratified
epithelium

31. Esophagus and trachea, monkey – glands in trachea
Esophagus
Trachea, whose lumen is lined with
pseudostratified ciliated
epithelium with goblet cells
Trachea
Thick hyaline cartilage bridged by smooth
muscle bundle posteriorly
Submucosa
with glands
Elastic fiber layer
beneath the epithelium

32. Trachea epithelial lining
Pseudostratified, ciliated, columnar epithelium from cat trachea.
25 µm

33. Trachea, monkey
Pseudostratified ciliated
epithelium with goblet cells
Thick basement membrane
Goblet cell
Rich vascular
supply to warm air
Plasma cells to produce antibodies

34. Trachea, monkey
Trachea, whose
lumen is lined with
pseudostratified
ciliated
epithelium with
goblet cells
Submucosa
with glands
Thick hyaline cartilage

35. Trachea (rat) Tracheal wall
50 µm
Submucosal glands
lumen
epithelium
submucosal glands

36. EM 8 trachea;
20630x
1. Mucous
2. Microvilli
3. Cilia
4. Goblet cell

37. Trachea (cat) Stained for elastic fibres
50 µm
Elastic fibres below the epithelium. They are part of the elastic continuum of the lung.
Add to the elastic recoil of the lungs after inspiration and expiration.
epithelium
pseudostratified
columnar, ciliated.
band of black stained
elastic fibres in
lamina propria.

38. Intrapulmonary bronchi
 Mucosa: resp. epithelium w/
goblet
 Muscle: SM
 Cartilage: hyaline cartilage
plates
 Glands: serumocous

40. Lung (adult) Bronchus
Low magnification view of bronchus.
Plates of cartilage can be identified.
1.0 mm
cartilage
cut edge of section
lumen

41. Lung (adult) Bronchus
250 µm
C
C : cartilage
M : smooth muscle
epithelium
lumen
G : glands
M
G

42. Lung (adult) Bronchus
25 µm
Typical respiratory tract epithelium lines the bronchus.
Pseudostratified, ciliated, columnar with goblet cells.
Further down as the bronchus gets smaller the epithelial lining also reduces in
height.
cilia
RB : blood cells
in capillary
G : goblet cells
mucous on surface
RB
G
G

43. SLIDE 67 Lung (adult) – Bronchus
Bronchus and blood vessels
0.5 mm
BR : bronchus
BV : blood vessel
BR
BV

44. Lung (adult) – Bronchus
Although there is little evidence of cartilage in this structure, some glands can be seen
suggesting that this is a small bronchus.
250 µm
glands

45. Bronchus (40x) - Slide 70: Mammalian Lung
1. Lumen
2. Pseudostratified ciliated epithelium
3. Mixed glands in the submucosa
4. Hyaline cartilage
5. Alveoli

46. 1. Lumen
2. Pseudostratified ciliated epithelium
3. Lamina propria
4. Smooth muscle
5. Mixed glands in the submucosa
6. Hyaline cartilage
Bronchus (100x) - Slide 70: Mammalian Lung
http://cal.vet.upenn.edu/projects/histo/Labrespiratory.htm

47. Lung (adult)
Smooth muscle runs in a spiral around the bronchus.
100 µm
epithelium
cartilage
glands
muscle
blood vessel

48. Bronchi vs. Trachea
 Various layers of the bronchi are thinner
than the trachea.
 Mucous & basal cells decrease &
bronchiolar exocrine cells increase in
number.
 Cartilage rings replaced by cartilage
plates.
 Location of the smooth muscle – between
the mucosa & submucosa; arranged in a
circular fashion.

49. Bronchioles
 Lining: ciliated simple columnar
to cuboidal epithelium
 Clara cells (bronchiolar exocrine
cells).
Clara cells – interspersed among ciliated cells; nonciliated
cells that have a characteristic rounded apical projection.

50. Diagram of a Clara cell between bronchiolar ciliated epithelial
cells.

51. Terminal Bronchioles
 Most distal part of the conducting
portion of the RS.
 Lined by simple cuboidal
epithelium w/ Clara cells.
 CT & muscle greatly reduced.

53. Lung (adult) Bronchiole
250 µm
Cartilage is absent from the wall of a bronchiole.
To allow a change in diameter. They must be flexible in a way that minimises ‘dead
space’ but does not cause too great a resistance to air flow.
epithelium
M : muscle
M

54. TERMINAL BRONCHIOLE
CLARA CELLS
Respiratory BRONCHIOLE
Ciliated cells
Elastic fibers
Smooth
muscle
Smooth
muscle cells
Cells in the respiratory
portion

55. SEM of a terminal
bronchiole. A longitudinal
section of terminal
bronchiole & surrounding
alveoli.
CLARA CELLS –
secrete a surface-active
agent that prevents
luminal adhesion should
the wall of the airway
collapse on itself.

56. Lung with bronchi
Bronchus
Bronchus
Elastic
artery
Conducting
bronchiole
Bronchus

57. Lung (bronchus)
Bronchus:
1) pseudostratified ciliated
columnar epithelium
with goblet-cells;
2) smooth muscle band
between the lamina
propria and the cartilage.
The smooth muscle is not
continuous around the
bronchus as it spirals.
3) a change from cartilage
rings to cartilage plates
surrounding the tube;
4) glands in the
submucosa.
Bronchioles:
1) have a ciliated
columnar epithelium;
2) do not have cartilage
plates or glands;
3) have well organized
muscle layers.

58. Bronchus vs. Bronchiole
Bronchus Bronchiole
Lining cells
Cartilage
present absentMucosal glands
pseudostratified ciliated
columnar epithelium
ciliated columnar epithelium
plates of cartilage cartilage absent

59. Lung (adult)
At low magnification identify : bronchus
bronchiole
large blood vessels
1.0 mm
blood vessels
bronchus
bronchiole

60. Respiratory portion
 Respiratory
bronchiole
 Alveolar ducts
 Alveolar sacs
 Alveolus

61. Respiratory portion
 Gas exchange area/parenchyma
 ACINUS – functional unit of GEA.
include respiratory bronchioles,
alveolar ducts, alveolar sacs &
alveoli.
 LOBULE – structural unit of GEA.
 cluster of acini separated by
interlobular septa.

62. Species differences
 Lungs of cattle, sheep & pigs –
complete septa (highly lobulated).
 Lungs of horses – incomplete
septa (poorly lobulated).
 Carnivores – do not have
interlobular septa.

63. Respiratory bronchiole
 Similar to the terminal bronchioles,
except that the epithelium is
interrupted by alveoli.
 Epithelium consists almost entirely
of Clara cells.

64. Lung (adult) Respiratory Bronchiole
Respiratory bronchioles are lined by a cuboidal epithelium.
Alveolar ducts open into alveoli.
100 µm
blood vessel
alveoli

65. Alveolar ducts
 Elongate airways that have almost
no walls, only alveoli, as its
peripheral boundary.
 Lined by simple squamous
epithelium.
 Terminate in clusters of alveoli –
alveolar sacs.

66. Alveoli
 Terminal air spaces of the
respiratory system & are the actual
sites of gas exchange.
 Cells in alveolar lining:
1. Type I pneumocytes (lining cells)
2. Type II pneumocytes (produce
surfactant)

67. Alveoli
 Terminal air spaces of the respiratory
system & are the actual sites of gas
exchange.
 Cells in alveolar lining:
1. Type I pneumocytes (lining cells)
2. Type II pneumocytes (produce surfactant)

68. Terminal and Respiratory Bronchioles (40x) - Slide 16:
Mammalian Lung
http://cal.vet.upenn.edu/projects/histo/Labrespiratory.htm
1. Terminal bronchiole
2. Respiratory bronchiole
3. Respiratory bronchiole to
alveolar duct
4. End of alveolar duct
5. Alveolar sac
6. Alveoli
7. Smooth muscle

69. Terminal and Respiratory Bronchioles (100x) - Slide 16:
Mammalian Lung
1. Terminal bronchiole
2. Respiratory bronchiole
3. Smooth muscle
4. Alveolar duct
5. End of Alveolar duct
6. Alveolar sac
7. Alveoli
http://cal.vet.upenn.edu/projects/histo/Labrespiratory.htm

70. Aveolar Sac (100x) - Slide 72: Mammalian Lung
1. Alveolar sac
2. Alveoli
3. Elastic fiber
http://cal.vet.upenn.edu/projects/histo/Labrespiratory.htm

71. 1. Type I pneumonocyte
2. Type II pneumonocyte
• Extremely thin squamous cells that line most (97%) of the surface of the alveoli.
• A cuboidal cell with a central nucleus; it covers the remainder of the interalveolar septal
surface (3%)
• Surfactant – decreases the alveolar surface tension and actively clears foreign materials.

72. Type II pneumonocyte (EM 18c).
1. Nucleus
2. Surfactant bodies

73. Surfactant
bodies in
Type II cells
Type II pneumocytes

74. Macrophages in Air Space of Alveoli
Alveolus
Air space

75. Lung (marsupial mouse) alveolar phagocytes
25 µm
P : phagocytes
PP

76. Lung stained for elastic tissues
Note the distribution of these fibres throughout the section especially in relation to the
alveolar ducts and alveoli.
100 µm
elastic fibres
surrounding alveoli
elastic fibres and
smooth muscle cells
below the cuboidal
lining of the alveolar
ducts

77. Lung
Mesothelium and connective tissue
of lung capsule
Type I & Type II pneumocytes
Alveolar macrophageCapillary endothelial cells and fibroblasts

78. Alveolus
(Air)
Capillary
(Blood)
Oxygen
CO2
Respiratory Portion
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Alveoli

80. Scanning electron micrograph of adult sheep lung
50 µm
B : cut bronchioles
alveoli
B
B

81. Lung
Bronchus Respiratory bronchiolesConducting bronchiole
Alveolar duct
Alveolar sac
Alveoli
The air-conducting tubes of the respiratory
system can be thought of as a series of
ducts which carry air to the sites of
gaseous exchange - the alveoli

82. Lung (adult) Respiratory duct/sac
The lips of the alveoli contain smooth muscle.
Respiratory bronchiole → alveolar ducts → alveolar sacs → alveoli.
100 µm
A
AS
AD
A : alveoli
AS alveolar sacs
AD alveolar ducts
A

83. Bronchus
Conducting bronchiole
Respiratory bronchiole
Alveolar duct
Alveolar sac
Alveoli
Mast cell
Mesothelium
Alveolar
macrophage
Type II pneumocyteType I pneumocyte
Lung (mast cells)
Terminal bronchiole

84. Mast cells function in the localized release of many bioactive substances
with roles in the local inflammatory response, innate immunity, and tissue
repair.
Mast cell granules normally contain: heparin, histamine, serine proteases,
eosinophil and neutrophil chemotactic factors, cytokines, etc.
48
Mast cells
Type II pneumocyte

85. Air
Blood
Air
Blood

86. Pleura
 VISCERAL (PULMONARY) PLEURA
– serous membrane that completely
covers both lungs, except at the
hilum & pulmonary lig.
 Lined by a squamous to cuboidal
mesothelial cells.

87. Lung (adult)
1 mm
Visceral pleura.
outer surface of lung covered by
visceral pleura
B : blood vessels
small bronchus
B
B

88. Lung (adult)
Visceral pleura.
100 µm
surface mesothelium
connective tissue layer
with elastic fibres

89. Avian Lung
 The duct system bears no similarity to
that in mammals.
 The primary bronchi enter the lung and
expand as the vestibulum.
 The latter continues through the lung as
the mesobronchus and is connected to
the abdominal air sac.
 Secondary bronchi give rise to tertiary
bronchi (parabronchi).

90. Avian Lung
 The parabronchi are analogous to the
alveolar duct of mammals.
 Atria project radially from the
parabronchi. These atria are continuous
with the air capillaries.
 The air capillaries are responsible for the
actual exchange of gases with the closely
associated vascular capillaries.

91. Avian Lung
 The air sacs associated with the avian
lung aid in the movement of air through
the lung.
 They are membranous structures, which
do not contribute to the exchange of
gases.
 Most birds have nine air sacs: single
(unpaired) cervical, paired claviculars,
paired cranial thoracics, paired caudal
thoracics, paired abdominals.

92. Avian
THE LUNG OF THE FOWL

93. Trachea (25x) - Slide C15: Avian Trachea
1. Tracheal lumen
2. Pseudostratified ciliated columnar
Jeepithelium
3. Complete hyaline cartilage ring
http://cal.vet.upenn.edu/projects/histo/Labrespiratory.htm

94. Avian Lung (25x) - Slide C17: Avian Lung
1. Parabronchus in l.s.
2. Parabronchus in x.s.
3. Atria
http://cal.vet.upenn.edu/projects/histo/Labrespiratory.htm

95. Summary Table of Respiratory System (Nasal cavity)
Region Skeleton Glands Epithelium Cilia Goblet Special
features
Vestibule Hyaline
cartilage
Sebaceous &
sweat g.
SSK No No Vibrissae
Respiratory Bone &
hyaline
cart.
Serumocous PCC Yes Yes Large
venous
plexus
Olfactory Nasal
conchae
Bowman’s g. PCC Yes Yes Basal cells;
sustentacul
ar, olfactory
cells; nerve
fibers

96. Summary Table of Respiratory System (Pharynx)
Region Skeleton Glands Epithelium Cilia Goblet
Nasal Muscle Seromucous PCC Yes Yes
Oral Muscle Seromucous SSE-NK No No

97. Summary Table of Respiratory System (Larynx)
Skeleton Glands Epithelium Cilia Goblet Special
features
Hyaline &
elastic
cartilage
Mucous &
seromucous
SSE-NK
& PCC
Yes Yes Vocal
cords,
epiglottis,
some taste
buds

98. Summary Table of Trachea & Primary Bronchi
Skeleton Glands Epithelium Cilia Goblet Special
features
C-rings of
hyaline
cartilage
Mucous &
seromucous
PCC Yes Yes Trachealis
m.; elastic
lamina

99. Summary Table of INTRAPULMONARY CONDUCTING
Region Skeleton Glands Epithelium Cilia Goblet Features
SECONDARY
BRONCHI
Plates of
hyaline
cartilage
Seromucous PCC Yes Yes 2 helically
oriented
ribbons of
smooth mucle
BRONCHIOLES Smooth m. None Simple
columnar to
simple
cuboidal
Yes Only
in
larger
bronc
hioles
Clara cells
TERMINAL
BRONCHIOLE
Smooth m. none Simple
cuboidal
Some None Clara cells

100. Summary Table of RESPIRATORY REGION
Region Skeleton Glands Epithelium Cilia Goblet Features
RESPIRATORY
BRONCHIOLE
Some
smooth m.
None Simple
cuboidal &
simple
squamous
Some None Outpocketings
of alveoli
ALVEOLAR
DUCT
None None Simple
squamous
None None Outpocketings
of alveoli; type
I & II
pneumocytes;
dust cells
ALVEOLUS None None Simple
squamous
None None Type I & II
pneumocytes;
dust cells