The document summarizes the histology of the respiratory system. It describes the structure of the trachea, bronchi, bronchioles, and lungs. The trachea has ciliated pseudostratified epithelium and incomplete hyaline cartilage rings. The bronchi have plates of cartilage instead of rings and a smooth muscle layer between the lamina propria and submucosa. Bronchioles lack cartilage and glands. Terminal bronchioles have Clara cells and cuboidal epithelium. Respiratory bronchioles have alveoli in their walls. The lungs contain alveolar ducts, alveoli lined with simple squamous epithelium, and macrophages in the interalveolar septa.

1. RESPIRATORY SYSTEM HISTOLOGY
• Trachea • Bronchus • Bronchiole •
Lung
Gaonkar Pankaj Prakash.
pankajgaonkar12993@gmail.com
Nagpur Veterinary College,
Maharashtra Animal & Fishery Sciences University, Nagpur, India

3. Trachea:-
•Trachea is lined by a ciliated pseudodtratified columnar epithelium with goblet
cells.
•A lamina propria and submucosa lie below the epithelium,but are not clearly
demarcated from one another.
•Glands,mostly mixed,occur in deeper layers of lamina propria and within the
submucosa.
•Rings of hyaline cartilage which are incomplete dorsally,support the tracheal wall.
•A layer of smooth muscle,the trachealis muscle is located dorsally in the trachea.
•It is positioned internal to the gap in the
tracheal cartilages in the horse,pig and
ruminants.
It lies external to the gap in cat and dog.
•An adventitia of connective tissue
completes the wall of trachea.

5. 3.Elastic fiber 15.sub-mucosa
11.Pseudostratified epithelium
12.Serous glands
17-trachealis muscle

6. 5.Hyaline Cartilage
9.Perichondrium (C.T. that envelops cartilage where it is not at a joint)
10.Pseudosrtatified epithelium
12.Trachealis muscle

7. 4.Goblet Cells
6.Lamina Propria

8. Bronchus
•The trachea bifurcates into two primary bronchi, which enter the lung and then branch
several times to give rise to smaller secondary and tertiary bronchi.
• Bronchi differ from the trachea in having plates rather than rings of cartilage, and in having
a layer of smooth muscle between the lamina propria and submucosa.

9. 4 – Elastic band
6- Hyaline cartilage
7-lamina propria
9-mixed gland
10-muscularis
11-pseudostratified epithelium

10. Bronchioles
•Bronchioles are smaller branches of the bronchi, and are distinguished from them by
the absence of cartilage and glands.
Terminal bronchioles :-
•No cartilage but smooth muscle.
•Clara cells present .
•smallest conducting bronchioles consist of a simple cuboidal (or perhaps “low
columnar”) epithelium of mostly exocrine cells, a few ciliated cells, and NO goblet cells, and are
called terminal bronchioles .
Respiratory Bronchioles:
You might see short, transitional regions of bronchioles which have alveoli in their walls. These
bronchioles with alveoli in their walls are called respiratory bronchioles.

11. Terminal bronchiole
Respiratory Bronchiole

14. 1- alveolus
2-bronchiole
6- Hyaline cartilage
11-pseudostratified epithelium
12-serous gland

15. 1- alveolus
2-bronchiole
3-columnar epithelium ciliated
8-Lymphatic Nodule
10-muscularis
12-serous gland

16. 3.Alveolus
5.Cuboidal epithelium
7.Macrophage
9.Resp. Bronchiole
10. Smooth muscle

17. Lung
• Bronchus and bronchioles are present
•Alveolar duct and alveoli- Simple squamous epithelium
•Macrophages or Dust cells (Heart failure cells)
•Inter alveolar septa & Supportive tissue

20. References
Available on request.