1. Histology of the Respiratory System
Department of histology, cytology and
embryology KhNMU

2. The respiratory system includes the lungs , system of passages (airways) and structures of ventilating mechanism, that link the site of gas exchange with the external environment. It is customary to divide the respiratory system into 3 principle regions:
a conducting portion, consisting of the nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles.
a respiratory portion, consisting of respiratory bronchioles, alveolar ducts, atria, alveolar sacs and alveoli.
ventilating mechanism , which creates pressure differences that move air. It includes the diaphragm, rib cage, intercostal muscles, abdominal muscles and elastic connective tissue in the lungs.

3. Development of the Respiratory System
Developmental Stages (Human)
1.Embryonic phase (3-7 weeks)
Initial budding and branching of the lung buds from the primitive foregut.
Ends with the development of the presumptive broncho-pulmonary segements.
Presumptive -
1 : based on probability or presumption
2 : being an embryonic precursor with the potential for forming a particular structure or tissue in the normal course of development

4. 2.Pseudoglandular phase (7-16) weeks
Further branching of the duct system (up to 21 further orders) generates the presumptive conducting portion of the respiratory system up to the level of the terminal bronchioles. They are embedded within a rapidly proliferating mesenchyme. The structure has a glandular appearance.

5. 3. Canalicular phase (16-24) weeks
The onset of this phase is marked by extensive angiogenisis within the mesenchyme that surrounds a dense capillary network. The diameter of the airways increases with a consequent decrease in epithelial thickness to a more cuboidal structure. The terminal bronchioles branch to form several orders of respiratory bronchioles. The developing respiratory tree, giving rise to chondrocytes, fibroblasts and myoblasts.

6. 4.Terminal sac phase (24-36) weeks
Branching and growth of the terminal sacs or primitive alveolar ducts. Functional type I & type-II pneumonocytes differentiate via several intermediate stages from pluripotent epithelial cells in the prospective alveoli. These cells then flatten, increasing the epithelial surface area by dilation of the saccules, giving rise to immature alveoli. Maturation of the alveoli continues by further enlargement of the terminal sacs, deposition of elastin foci and development of vascularised septae around these foci.

7. 5.Alveolar phase (36 weeks - term/adult)
Maturation of the lung indicated by the appearance of fully mature alveoli begins at 36 weeks, though new alveoli will continue to form for approximately three years.
A decrease in the relative proportion of parenchyma to total lung volume still contributes significantly to growth for 1 to 2 years after birth, thereafter all components grow proportionately until adulthood.

8. There are changes in the epithelial lining of the respiratory tree as one proceeds from the nasal cavity to the alveoli of the lungs: Pseudostratified Columnar Ciliated=> Simple Columnar =>Simple Cuboidal => Simple Squamous Epithelium.

9. Conducting Portion System of ducts Nose Nasopharynx Larynx Trachea
Conducts air to all parts of the lungs
Nose
Nasopharynx
Larynx
Trachea
Bronchi
Bronchioles
Preterminal bronchioles
Terminal bronchioles
Conditioning of the air
Warming, moistening and removal of particulate materials

10. Trachea 20 C-shaped cartilaginous rings Paries membranaceus
Connective tissue that fills gap between the two posterior ends
Neighbouring rings
Connected by regular dense connective tissue
Continuous with perichondrium of cartilaginous rings

11. Trachea
1. Mucosa
Pseudostratified columnar epithelium with cilia and goblet cells
2.Lamina propria,Elastic & Collagen fibers 3.Submucosa Mixed glands and lymph follicles
4. Fibrocartilagenous Layer Hyaline Cartilage & SMC
5.Adventitial layer

12. Low Magnification of a Cross Section Through the Trachea
1. Lumen
2. Pseudostratified
ciliated columnar epithelium
3. Submucosa
4. Hyalin cartilage
5. Perichondrium
6. Adventitia
7. Mixed glands
8. Secretory duct

13. Epithelium of the Trachea
Lumen 2. Cilia 3. Columnar
epithelial cells 4. Basal membrane 5. Lamina propria 6. Basal cell layer 7. Goblet cell

14. Respiratory epithelial cell types
1.Ciliated columnar cells
2.Mucous goblet cells
3.Brush cells
4.Basal cells
5.Small granule cells

15. Bronchi Extrapulmonary bronchi Two primary bronchi
Histologically similar to the trachea
Intrapulmonary bronchi
Secondary bronchi (Lobar) - 5
Bronchopulmonary segmental bronchi –Tertiary (Lobular)- 20

16. Intrapulmonary Bronchi
Mucosa
Pseudostratified columnar containing cilia and goblet cells
Lamina propria - elastica changes into longitudinally arranged elastic fibers
Smooth muscle
Between mucosa and cartilage
Mixed glands - between muscle layer and cartilagous plates
Cartilage
Irregular shaped cartilaginous plates

17. Three-dimensional Representation of an Intrapulmonary Bronchus
Bronchi
Three-dimensional Representation of an Intrapulmonary Bronchus
cartilage plate
lamina propria
pseudostratified columnar epithelium with cilia
and goblet cells
smooth muscle

18. Bronchioles Branches of bronchi Penetrate lung lobule at its apex
Preterminal bronchiole inside the lobule
Preterminal bronchiole
Branches into terminal bronchioles
Branch further

19. Bronchioles Mucosa Epithelium in the larger bronchioles
Simple columnar epithelium with cilia
Tall, non-ciliated secretory cells – cells of Clara
In smaller bronchioles
Tall cuboidal epithelium
Goblet cells have disapeared higher up in the bronchioles
Lamina propria
Thin elastic layer

20. Bronchioles Muscle layer Connective tissue
Same as that of the bronchi
Connective tissue
Attaches bronchioles to surrounding tissue
No glands or cartilage are present

21. Terminal bronchioles – end point of Conducting portion Respiratory bronchioles – beginning of Respiratory Portion

22. Respiratory Portion
Consists of smaller ducts and sacs
Respiration takes place
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Alveoli

23. Respiratory Bronchioles
Schematic of the Respiratory Portion of a Lung Lobule
Respiratory bronchioles
Branch from terminal bronchioles
Alveoli
Thin bulging sacs in walls
Gas exchange takes place
Smooth muscle
respiratory bronchiole
alveolar ducts
alveoli
interalveolar septum
sacculus alveolaris

24. High Magnification of the Lung Demonstrating a Respiratory Bronchiole
High cuboidal
epithelium 2. Alveolus 3. Interalveolar
septum 4. Lumen

25. Alveolar Ducts, Alveolar Sacs and Alveoli
Long passages into which respiratory bronchioles open
Alveolar ducts open directly into small spaces
Alveoli
Interalveolar septa
Separate neighboring alveoli
Alveolar sacs
Air spaces surrounded by clusters of alveoli
Elastic and reticular fibers
Arranged around the capillaries

26. 1. Alveolar sacs 2. Alveoli 3. Interalveolar septa

27. Blood – Air Barrier Separation Between Air and Bloodstream
Cytoplasm of epithelium lining the alveoli
Basal lamina of the epithelium
Basal lamina of the capillary endothelium
Cytoplasm of capillary endothelium

28. Alveolar epithelium – Pneumocytes Simple squamous alveolar epithelial cells – Type 1 cells -Thin cytoplasm Large Secretory cells – Type 2 (secretory cells) - Secrete surfactant & Decrease surface tension Alveolar macrophages - Type 3 (dust cells)

29. Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells. It is 2-layer molecular film on the alveolar surface. The proteins and lipids that comprise the surfactant have both a hydrophilic region and a hydrophobic region. The main lipid component of surfactant, (DPPC)- dipalmitoylphosphatidylcholine.

30. Functions of surfactant 1. Decrease surface tension 2
Functions of surfactant 1.Decrease surface tension 2.To increase pulmonary compliance 3.To prevent atelectasis (collapse of the lung) at the end of expiration. 4.To facilitate recruitment of collapsed airways.

31. Pulmonary Surfactant

32. Pores and Lambert-sinuses
Alveolar pores
Direct contact between 2 alveoli
Infections can spread from one lobe to another via this route
Lambert sinuses
Short cannel
Connects terminal bronchioles with alveoli

33. Acinus is a Structural and Functional Unit of the Lung

36. Terminal Part of the Lungs