1. Respiratory System Histology
Dr. Nabil Khouri MD, MSc. Ph.D

2. Respiratory system Airways – conducting portion Lung
Nasal cavity
Pharynx (naso – oro –laringo-)
Larynx
Trachea
Bronchi (extra pulmonary)
Lung
Conducting portion
INTRAPULMONARY BRONCHI
BRONCHIOLES
TERMINAL BRONCHIOLES
Respiratory portion
RESPIRATORY BRONCHIOLES
ALVEOLAR DUCTS
ALVEOLI

3. Conducting portion Nasal Cavity
Nasal cavity composed of three regions( vestibule, respiratory and olfactory regions)
Anterior portion – Vestibule: vibrissae – skin - sebaceous + sweat glands
Posterior aspect – nasal fossae: conchae (sup, mid, inf), olfactory region,
arterial plexuses and venous sinuses  bleeding

4. Vestibule
Anterior portion of nasal cavity near of the nares dilated and known as the vestibule
lined with skin and has short, stiff hairs named VIBRISSAE that prevent large dust particles to enter
It is made of Keratinized stratified squamous epithelium
And Non Keratinized stratified squamous epithelium
Dermis houses numerous sebaceous glands

5. Posterior aspect of Nasal cavity
Is lined by Pseudostratified ciliated columnar epithelium (RESPIRATORY EPITHELIUM)
Cellular content of the respiratory epithelium
Ciliated columnar cells: Most common, each cell has about 300 cilia
Goblet cells: Secret mucous (Found in frequency)
Brush cells: Have short microvilli, nerve fibers, sensory function
Basal cells: Are rounded STEM CELLS that located near basal lamina and show mitotic figures
Small granule cells

7. Nasal Cavity

8. The Lamina Propria (Subepithelial CT)
Mucous Glands
Serous Glands
Venous Sinuses
lymphoid elements
CT Lamina Propria
Is richly vascularized, containing large arterial plexuses and venous sinuses, many
Secretions of nasal mucosa
- Bactericides
- Lysozymes

9. Olfactory region The olfactory epithelium
Lamina propria (serous secreting BOWMAN’S GLANDS (Boumans GL) a rich vascular plexus and many axons arising from olfactory cells of the olfactory epithelium)

10. olfactory epithelium comprises three types of cells:
Olfactory cells olfactory cells are bipolar neurons whose apical aspect (dendrite) is modified to form a bulb known as olfactory vesicle
Sustentacular cells (Supporting Cells)
Cells that has a striated border composed of microvilli, and secretory granules
They provide physical support, nourishment
Basal cells
Are short basophilic cells
Their apical aspects do not reach the epithelial surface they proliferate and replace both two other cells

11. Olfactory Epithelium
(bipolar neurons)
(Sustentacular cells)

12. Transition between the Naso and the Oro-pharynx

13. The naso-pharynx The upper part of the pharynx which –
Anteriorly is open into the nasal cavity through posterior nares,choana!
Posteriorly and laterally is surrounded by the muscular tissue
caudally is continued with the oropharynx and larynx
the epithelium of the pharynx is PSEUDOSTRATIFIED CILIATED COLUMNAR
goblet cells and small glands (mucous, serous and mixed)
Accumulations of lymphatic tissue
pharyngeal tonsil – posteriorly
Tubal tonsils – laterally both are found in the lamina propria
The middle layer of the pharynx is of muscular character being formed by bundles of the striated muscles

15. Pharynx
Oro-pharynx
It is lined by a STRATIFIED SQUAMOUS NON-KERATINIZING TYPE OF EPITHELIUM and lacks both muscularis mucosae and submucosa.
The epithelium rests on a lamina propria that contains a thick layer of longitudinally oriented elastic fibers that appear dark, glassy red located near the underlying muscularis externa.
Lamina propria – loose-dense irregular CT
Vascularized
Seromucous gland: Mucous glands seen in this muscular layer in some of our glass slides are the extensions of those present in the lamina propria.
Lymphoid tissue – posterior: pharyngeal tonsil
Skeletal muscle-epimysium
The muscularis externa is composed of somewhat irregularly arranged skeletal muscle, the longitudinal and constrictor muscles of the pharynx.

16. Larynx – voice box Additional function: Phonation
Prevent food/drinks – respiratory system
Tube : cartilage (hyaline, elastic) – ligaments – skeletal muscles (intrinsic-extrinsic)
Epiglottis – elastic cartilage
Stratified squamous non keratinized epithelium
Pseudostratified (respiratory epithelium)
Vestibular fold – false vocal cord (superior)
Vocal fold - true vocal cord (inferior) - stratified squamous
Vocalis muscle
vocal ligament – regular dense elastic CT

19. Epiglottis is an elastic cartilage of larynx
It is lined by stratified squamous epithelium on lingual surface
Pseudostratified ciliated columnar epithelium lined the laryngeal side
Serous and mucous glands located in lamina propria

20. Trachea–extrapulmonary bronchus
Mucosa
Respiratory epithelium – Pseudostratified ciliated columnar epithelium: goblet, cilated columnar, basal, brush, serous, DNES cells
Lamina propria – loose fibroelastic-mucous, seromucous gl-lymphoid tissue --elastic lamina
Submucosa-dense irreg. fibroelastic CT, mucous-seromucous gl- lymphoid tissue
Adventitia – fibroelastic CT - C ring hyaline cartilage (p cartilaginea) – fibrous CT – smooth muscle (p. membranacea)

21. Lamina propria
composed of loose fibroelastic CT, contain seromucous glands and lyphoid elements, elastic lamina separate this layer from submucosa
Submucosa
Subnucosa is composed of dense irregular fibroelastic CT that houses mucous and seromucous glands, rich in blood and lymph supply
Adventitia
Adventitia is a fibroelastic CT that houses C-shaped hyaline cartilage, at posterior aspect of cartilage, there is a dense band of smooth muscle cells known as trachealis muscle

23. Trachea
The Mucosa
Respiratory epithelium composed of 6 cell types located on a thick basement membrane
Goblet cells are about 30% of cells, produce mucinogen
Ciliated columnar cells about 30% of cells, are tall which have cilia and microvilli
Basal cells are also about 30% of cells, they are undifferentiated stem cells
Brush cells are just 3% of cells, they are narrow columnar cells that their function is unknown, but nerve ending associated with them
Serous cells are about 3% of cells, they are columnar and have serous granule
DNES cells, constitute about 3-4% of cells, have numerous granule in basal cytoplasm which is contain various pharmacological agents

25. Lung
Intrapulmonary bronchus (2ndary -3tiary: lobe – broncho pulmonary segment)
Mucosa –folded app
Respiratory epithelium
L propria – fibroelastic-seromucous gl-lymphoid nodules
--Smooth muscles-spiral
Submucosa-seromucous gl-lymphoid nodules
Adventitia – plates of cartilage (hyaline)
Bronchioles
Mucosa
Pseudostratified columnar epithelium- goblet cells  ciliated simple columnar ciliated cuboidal (with Clara cells)
Lamina propria
No glands
Elastic fibers
Smooth muscles – helical loose meshwork – surrounded by fibroelastic CT

26. Bronchial Tree is composed of: 2 primary bronchus that enter lungs
3 lobar ( secondry) bronchus on right and 2 on the left
Segmental (tertiary) bronchus
bronchioles
Terminal bronchioles
Respiratory bronchioles
Progressively airways decreased in size and cartilage, glands, goblet cells, and the height of epithelial cells
But increase smooth muscle cells and elastic tissue

27. Primary Bronchi (Extrapulmonary)
Primary bronchi is identical to trachea, but have smaller diameter and thinner wall
Cartilage is in form of irregular plates
Smooth muscle located between lamina propria and submucosa as 2 distinct layers PB

29. Bronchioles have no any cartilage or glands but have few Goblet cells
In larger bronchioles epithelium is simple columnar ciliated, with occasional goblet cells
In smaller bronchioles epithelium change to Simple cuboidal, with no goblet cells
Bronchioles have a smooth muscle coats surrounded by fibroelastic connective tissue
Terminal bronchioles are terminus of conducting portion
they are lined by cuboidal cells(some with cilia) and Clara cells which have domed apical surface
Lamina propria
is a fibroelastic CT, 1-2 layer of smooth muscle cells separate it from adventitia
CLARA CELLS ( exocrine bronchiolar cells)
Clara cells are columnar with dome-shaped apex
Secretory granules which secret glycoproteins and surfactant-like materials
degrade toxins(SER)
divide to replace other cells
antimicrobial peptide

31. Terminal Bronchiole

33. Respiratory Bronchioles
are a transitional zone between conducting and respiratory tissues
Alveoli branching from their walls
are lined by ciliated cuboidal epithelium with Clara cells that change to type I alveolar cells
Smooth muscle cells and elastic fibers underlie epithelium

34. Respiratory Bronchiole

36. Alveolus Small air sac - gas exchange
Between alveoli – interalveolar septum – alveolar pores
Connective tissue: elastic, reticular (coll III) – lymphoid tissue
Macrophages, fibroblast, myofibroblast, mast cells
Continuous capillary bed (from pulmonary artery  vein)
Both side
Type I Pneumocytes/alveolar cells - squamous alveolar cells) – tight junction – basal lamina – very thin region  permeable to gasses
Type II Pneumocytes/alveolar cells - great alveolar cell – septal cells – surfactant – surface tension↓  ≠ collapse

37. Alveolar walls & Alveolar cells

38. Cells of the Alveolar Septa
Endothelial cells are nonfenestrated with a thin dark nucleus, and pinocytotic vesicles
Type I squamous cells that cover most of alveolar surface area, they have pinocytotic vesicles
Type II (greater alveolar) cells are cuboidal, located on alveolar surface where septa intersect, they have foamy cytoplasm, surfactant granules (reduces surface tension to keep alveoli open during expiration)
Alveolar macrophages that are known as dust cells
Interstitial cells consist of fibroblasts and mast cells
Elastic & reticular fibers

40. Type I pneumocytes (Squamus alveolar cells)
95% of the alveolar surface is composed of the simple squamous cells which are known as type I pneumocytes
occluding junction attaches to other cells
have basal lamina,
alveolar pore formed by fusion of two adjacent type I cells
Type II pneumocytes (Septal cells)
They are more numerous than type I
cover just 5% of the alveolar surface
located among type I cells, cuboidal with dome-shaped apical
Located where adjacent alveoli separated by septum
They have an abundance of RER, developed golgi complex, their lamellar bodies contain pulmonary surfactant

41. Type I Pneumocytes

42. Type II Alveolar or Type II pneumocytes
Also known as Septal cells
Rounded or cuboidal secretory cells with microvilli
Secretory granules are made of several layers- Multilamellar bodies.
These lamillar bodies are cytoplasmic inclusions made up of phospholipid which combines with other chemicals to form surfactant & then ooze out of the cell by exocytosis.
Pulmonary Surfactant – is the fluid secreted that spreads over the alveolar surface
These cells can multiply to replace damaged cells.
Surfactant also has bactericidal properties

43. Type I and II Pneumocytes, capillaries and Dust cells

45. Alveolar Macrophages or Dust cells
Derived from Monocytes and are part mononuclear phagocytic system.
Either seen in the septa or alveoli
Cytoplasm contains phagocytosed inhaled carbon and dust particles
Inhaled carbon and dust particles are passed on to them from pneumocyte I through pinocytic vesicles

46. Alveolar Macrophages or Dust cells
Migrate from septum to alveolar surface and are carried to the pharynx through sputum
Main function is to clean the alveoli of invading microorganisms and inhaled particulate matter by phagocytosis

47. Trachea
Bronchus
Tertiary bronchus
Bronchiole
Respiratory bronchiole
Epithelium
Pseudostratified è
Columnar
Cuboidal
Goblet cells
+++ ++ +
Absent
Clara cells
Muscularis mucosae
Mucous glands
Cartilage
Alveoli