Histology of respiratory system

Histology of respiratory system

2. The respiratory system functions in exchanging
carbon dioxide for oxygen.
Has two portions
◦conducting portion
◦respiratory portion
The luminal diameters of the various conduits
can be modified by the presence of smooth
muscle cells along their length

3. Extrapulmonary

Conducting Portion
1. Nasal cavity
2. Pharynx
3. Larynx
4. Trachea
5. Primary bronchi
Intrapulmonary

Conducting Portion
1. Secondary bronchi
2. Bronchioles
3. Terminal bronchioles

Respiratory Portion
1. Respiratory bronchioles
2. Alveolar ducts
3. Alveoli

5. Mucosa (mucous membrane)
Respiratory epithelium- Pseudostratified ciliated
columnar epithelium with numerous goblet cells.
Lamina propria of loose connective tissue with
blood vessels and nerves
Deepest layer of mucosa may consist of:
◦An elastic lamina or A muscularis mucosae or
◦This layer may be absent

6. Modulation of the temperature of the inspired air
is accomplished mostly in the nasal cavity by the
rich vascularity of the connective tissue just deep
to its respiratory epithelium.

Submucosa: - Dense irregular connective tissue
with mucous and serous (mixed) glands.
Cartilage or bone
Adventitia: - Loose connective tissue forming the
outer layer of the passageway

7. Layers become thinner as passageways
decrease in diameter.
Epithelium decreases in height from
pseudostratified to simple columnar to
simple cuboidal to simple squamous.
Goblet cells and mixed glands stop
relatively abruptly at the junction of a
secondary bronchus with
bronchiole.

8. Cartilage decreases in size, breaks up into
plates, and stops relatively abruptly at the
junction of a secondary bronchus with a
bronchiole.
Cilia are gradually eliminated.
Results in the formation of the wall of an
alveolus, where gas exchange occurs
Epithelium is simple squamous
Connective tissue core with numerous
capillaries

9. 1. Non-olfactory region
Nasal vestibule - is a dilated space of the
nasal cavity just inside nostrils and lined
by skin (Contains Vibrissae, Sebaceous glands)
Respiratory region - the largest part
(inferior 2/3) of the nasal cavities and
lined by “Typical” respiratory mucosa
◦lamina propria is firmly attached to the periosteum
and perichondrium i.e. the mucosa Lacks muscularis
mucosae and elastic lamina
The nasal cavities can be subdivided into two regions

11. Upside-down, U-shaped area in posterior, superior
region of each nasal fossa, extending over superior
conchae and about1cm down nasal septum
In living tissue, this mucosa is slight yellowish
brown color caused by pigment in the olfactory
epithelium and the associated olfactory glands.

12. Olfactory mucosa = is also pseudostratified columnar
epithelium composed of different cell types
Olfactory cells :- are Bipolar neurons that respond to
odors. A single dendrite extends to the surface to
form a swelling, the olfactory vesicle, from which
nonmotile cilia extend over the surface. These cilia
increase surface area and respond to odors.
Support cells: -are the most numerous cells, similar
to neuroglia cells and provide mechanical and
metabolic support to the olfactory receptor cells.
◦They synthesize and secrete odorant-binding proteins.
◦are columnar cells with numerous microvilli on apical
surface and nuclei occupy a more apical position

13. Basal cells are stem cells located on the basal
lamina from which new olfactory receptor cells
and supporting cells differentiate.
Brush cells are columnar cells with blunt
microvilli
specialized for transduction of general
sensation. (smaller numbers)
Their basal surface have synaptic contact with
trigeminal nerve fibers
Olfactory Mucosa lacks goblet cells

14. Note level of their nucleus

15. The lamina propria
◦directly contiguous with the periosteum of the
underlying bone
◦contains olfactory nerves in combination with
olfactory glands → identifying feature of the
olfactory mucosa
◦olfactory glands (Bowman’s glands), serous
glands whose watery secretions serves as a
trap, solvent & flush for odoriferous
substances.

16. lined by thin, ciliated,
pseudostratified
columnar respiratory
epithelium with
numerous goblet
cells.

17. connects the nasal and oral cavities to the larynx and
esophagus.
Divided regionally into nasopharynx and Oropharynx
The lining epithelium varies according to location.
Nasopharynx is covered, in most areas, by Pseudostratified
ciliated columnar epithelium with Goblet cells. The cellular
composition is similar with the nasal cavity epithelium.
Lymphatic nodules(pharyngeal tonsil) and diffuse lymphatic
tissue are present in its lamina propria. It lacks muscularis
externa of its own(muscles of head and neck.)
Stratified squamous epithelium covers regions of “wear and
tear” → Oropharynx and part of nasopharynx

18. Composition of the wall of the larynx
Mucosa
Epithelium
◦The luminal surface of the vocal cords is covered with
stratified squamous epithelium, as is most of the
epiglottis, because of friction incurred by rapidly
moving air.
◦The rest of the larynx is lined by Pseudostratified
ciliated columnar epithelium with goblet cells.
◦No muscularis mucosae or elastic lamina, so lamina
propria is continuous with submucosa.

19. Submucosa with mixed glands
◦except in true focal fold
Cartilages maintaining patency are numerous,
uniquely shaped and are either hyaline or elastic (the
epiglottis and the vocal processes of arytenoid).
An adventitia is present.
False vocal folds – Pseudostratified ciliated columnar
epithelium with goblet cell. But lacks muscularis
mucosae & elastic lamina.
◦Many nonsmoking adults and virtually all smokers exhibit
patches of stratified squamous epithelium

21. The trachea and primary bronchi are identical in structure
and will be considered together.
Mucosa - Pseudostratified ciliated columnar epithelium
with goblet and basal cells with an elastic, fiber-rich
Lamina propria
Submucosa- have a slightly denser CT than lamina
propria
C-shaped hyaline cartilage rings maintain patency;
trachealis muscle (smooth) interconnects the open ends
of the tracheal rings.
Adventitia - CT that binds trachea to adjacent structures.

23. Tracheal epithelium is similar to
respiratory epithelium in other parts of
the conducting airway.
It is composed of:-
1.Ciliated cells
◦most numerous of the tracheal cell types
◦Each cell has approximately 250 cilia.
◦Immediately below the cilia is a dark line
formed by the aggregated ciliary basal
bodies
◦function as a “mucociliary escalator”

24. 2. Mucous cells (goblet cells)
are interspersed among the ciliated cells and
extend through the full thickness of the
epithelium
Although the mucinogen is typically washed out in
H&E preparations, the cell is made apparent by the
remaining clear area in the cytoplasm and
the lack of cilia at the apical surface.
during chronic irritation of the air passages
mucous cells increases in number

25. 3. Brush cells
are columnar cells that bear blunt microvilli.
The basal surface of the cells is in synaptic contact
with an afferent nerve ending (epitheliodendritic
synapse).
◦regarded as a receptor cell.

4. Basal cells
maintains individual cell replacement in the epithelium.
most of the nuclei near the basement membrane belong
to basal cells.

27. 5. Small granule cells (Kulchitsky cells)
Are class of enteroendocrine cells of the gut
◦Development of respiratory system from primitive foregut
Solitary, sparsely dispersed among the other cell
types.
difficult to distinguish from basal cells in LM (silver
staining)
cytoplasm exhibits numerous, membrane-
bounded, dense-core granules → may release
vasoactive substances.

29. A thick “basement membrane” is characteristic of
tracheal epithelium.
◦may be considerably thicker in chronic smokers
lamina propria appears as a typical loose CT
◦is very cellular, containing numerous lymphocytes,
Plasma cells, mast cells, eosinophils, and fibroblasts.
◦Contains Lymphatic tissue, in both diffuse and nodular
forms → equivalent of bronchus-associated lymphatic
tissue (BALT)
The boundary between mucosa and submucosa is
defined by an elastic membrane.
◦the boundary is not obvious in H&E

30. is a relatively loose connective
tissue similar in appearance to
the lamina propria
Diffuse lymphatic tissue and
lymphatic nodules
characteristi-cally extend into
this layer from the lamina
propria.
contains the larger distributing
vessels and lymphatics

31. composed of mixed seromucous
Submucosal glands with simple
cuboidal epithelium lined duct
extending through the lamina propria
glands are especially numerous in the
cartilage-free gap posteriorly
◦Some penetrate the muscle layer at
this site and also lie in the adventitia.
This layer ends where its connective
tissue fibers blend with the
perichondrium of the cartilage layer.

32. The tracheal cartilages and
trachealis muscle separate
submucosa from adventitia.

Adventitia - contains the
largest blood vessels and
nerves that supply the
tracheal wall, as well as the
larger lymphatics that drain
the wall.

33. Are the first
intrapulmonary
structures; a secondary
bronchus supplies each
of the three lobes of the
right lung and the two
lobes of the left lung.
Are similar to, but
diminished in size from,
the primary bronchi

34.  Mucosa
◦Epithelium, pseudostratified with cilia and goblet cells
◦Lamina propria contains numerous, longitudinally
arranged elastic fibers.
◦Muscularis mucosae of smooth muscle fibers arranged in
crisscrossing bands
Submucosa with mixed glands
Patency maintained by plates of hyaline cartilage.
Adventitia is present.

35. Walls of bronchioles continue to
decrease in size.

Mucosa
Epithelium
◦Pseudostratified with cilia and goblet cells in
largest bronchioles that decreases to:
◦Simple columnar with cilia in smallest
bronchioles (terminal bronchioles), but no
goblet cells persist.
◦Terminal bronchioles lined with a simple
cuboidal epithelium in which Clara cells - tall,
dome-shaped, nonciliated cells

36. ◦Lamina propria contains numerous,
longitudinally arranged elastic fibers.
◦Muscularis mucosae. Greatest
development of smooth muscle
(crisscrossing bands) in relationship
to thickness of wall of all respiratory
passageways
Submucosa contains no glands.
No cartilages → submucosa and
adventitia form a single
connective issue layer.

37. Primary Function
Gas exchange occurs in
the alveolus. Therefore, an
alveolus must be an
integral part of all the
passageways of the
respiratory part of the
respiratory system.

38. Respiratory bronchioles continue
to decrease in diameter and in
thickness of their walls.
Mucosa. Simple cuboidal
epithelium with a few sparsely
scattered cilia and Clara cells
◦Elastic fibers in lamina propria
◦Muscularis mucosae of smooth muscle
Alveoli bulge from wall

39. An alveolar duct is formed as
the alveoli in a respiratory
bronchiole increase in number,
thereby decreasing the
amount of wall that is present.
◦Alveoli bulge from the framework
formed by the knobs.
Wall Simple cuboidal
epithelium
Elastic fibers and smooth
muscle

40. are components of respiratory
bronchioles and alveolar ducts,
or they may be grouped
together to form alveolar sacs.
Interalveolar septum Structure
between two adjacent alveoli is
composed of:
◦The epithelium lining each
alveolus
Squamous alveolar or type I
pneumocyte - form a simple
squamous epithelium lining
95% of the alveolar surface
area and forming a portion
of the blood-air barrier.

41. Septal or type II pneumocytes
◦account for 60% of the alveolar lining cells but cover only
about 5% of the alveolar air surface
◦Serve as progenitors for both type I and type II cells
◦are progenitor cells for type I alveolar cells
◦Spherical cells, bulging into alveolar space, cytoplasm
filled with granules (lamellar bodies) which give rise to
surfactant

Connective tissue core contains a vast capillary bed
that bulges into the alveolar space, elastic fibers,
and other connective tissue components.
Alveolar macrophages - function both in the CT
septum and in the air space of the alveolus

42. 

45. The air-blood barrier separates air from blood.
Oxygen and carbon dioxide must cross this barrier
during gas exchange.
Composition
◦Squamous alveolar cell with its basement membrane
◦Capillary endothelial cell with its basement membrane

46. Pulmonary surfactant deficiency
◦respiratory distress syndrome of the new born or hyaline
membrane disease in premature neonates.
Alveolar macrophages
◦in CHF “heart failure” cells
◦dust cells
Alveolar or Kohn’s pores.
◦Small openings in the interalveolar septa between
neighboring alveoli that aid in equalizing interalveolar
pressure.
◦contribute to the spread of bacteria in the lung.

47. The pleura is a serous membrane (serosa) covering
the lungs.
Composition
◦Simple squamous epithelium (mesothelium)
◦Underlying connective tissue layer with elastic fibers
Produces a fluid film that lubricates the surface of
the lungs and provides surface tension for lung
expansion

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