HISTOLOGY OF RESPIRATORY SYSTEM PART II.pptx

Histology of respiratory system

1. HISTOLOGY OF RESPIRATORY SYSTEM PART II Dr. Pradipta Ray Choudhury MBBS, MD, PhD ASSOCIATE PROFESSOR OF ANATOMY SMCH, SILCHAR

2. Bronchiole conducting tubules less than 1mm in diameter. formed by repeated division of the tertiary bronchi. their wall no longer contains cartilage & submucosal glands . bronchioles further divide to end in terminal bronchiole (last part of conducting system)

3. terminal

4. Histologically Bronchioles are characterised by the presence of the following features : Simple ciliated columnar or cuboidal epithelial lining with no goblet cells. goblet cells are replaced by Clara cells which secrete a glycoprotein that forms a protective layer of surfactant to reduce surface tension.

5. smooth muscle layer is prominent (under the control of vagus and sympathetic nerves). stimulation of vagus causes bronchoconstriction . Stimulation of sympathetic nerve causes bronchodilation . Many elastic fibres . No glands, No cartilage.

6. Terminal Bronchiole Simple Columnar Epithelium Prominent smooth muscle

7. Clinical Correlations: Asthma: Acute, episodic airway obstruction resulting from allergic condition. hyper-irritability of respiratory tract lead to excessive contraction of smooth muscle result in constriction of bronchi and bronchioles ( bronchospasm ). Thus leading to airway obstruction.

8. RESPIRATORY PART OF RESPIRATORY SYSTEM

9. The respiratory part of respiratory system : Includes- respiratory bronchiole -alveolar duct -alveolar sac -alveoli

10. Terminal bronchiole( end of conducting part) divides into respiratory bronchioles divide into a few alveolar ducts ends in a passage, the atrium leads into a number of alveolar sacs

11. each alveolar sac is studded with a number of air sacs or alveoli. (gaseous exchange occurs).

12. Respiratory bronchiole Less than 0.5 mm in diameter epithelium= simple cuboidal with cilia ; cilia gradually lost replaced by non ciliated cuboidal epithelium. histology is similar to that of terminal bronchiole i.e. Clara cells present smooth muscle layer present.

13. Alveolar duct and sacs: : arise from respiratory bronchiole. lined by squamous epithelial cells alveolar ducts open into atria, which comm - unicate with alveolar sacs and alveoli. Reapiratoty bronchiole

14. Alveoli - Alveoli form the parenchyma of lung. - lined by thin squamous epithelium thin walled sac-like evaginations present at the terminal part of bronchial tree. responsible for exchange of gases between air and blood. in section they resemble a honeycomb

15. -are separated by interalveolar septum. interalveolar septum contains a network of capillaries supported by reticular & elastic fibres , & occasionally fibroblasts, and macrophages. The septum may contain pores help in passage of air from one alveolus to another equalizes the pressure in neighbouring alveoli.

16. alveolus

17. The blood-air barrier : between blood in capillaries & air in alveoli 3 structures: continuous non-fenestrated endothelium of capillaries. squamous epitheium lining of alveoli. fused basal lamina of endothelium & epithelium. - thin facilitates diffusion of O 2 & CO 2

18. Structure of Alveolar Wall: alveolus has a very thin wall. types of cells ( pneumocytes ) present in the lining epithelium of the alveolus are: type I pneumocytes type II pneumocytes type III pneumocytes - occasional

19. (a) Type I pneumocytes /alveolar cells - are the squamous epithelial cells - cover 95% of alveolar surface. form part of the blood-air barrier.

20. (b) Type II pneumocytes /great alveolar cells - large rounded cells. - cover 5% of alveolar surface. bear microvilli on their apical surface. secrete surfactant spread over the alveolar surface lowers the surface tension prevents alveoli from collapsing during expiration.

21. - under EM, their cytoplasm contains secretory granules that appear to be made up of several layers (so called multilamellar bodies).

22. Type I pneumocytes Type II pneumocytes

23. (c) Type III alveolar cells/brush cells: occasionally found in alveolar epithelium. monitor the quality of air entering the lung .

24. Alveolar macrophages (dust cells): found in interalveolar septum sometimes migrate from septum to alveolar surface are first line of defense against pulmonary infection phagocytose dust particle seen in the cytoplasm of macrophages so called dust cells .

25. macrophage

26. In smokers, they engulf carbon & tar. In congestive heart failure (pulmonary capillaries overloaded with blood) RBC may accumulate in alveoli these macrophages phagocytose RBCs that escape from capillaries. acquire brick red colour heart failure cells

27. Clinical correlation : a) Pneumonia: An acute infection of lung microorganism enter lung produce toxin inflammation collection of exudate in alveoli interfere with ventilation & gas exchange. fever, cough, chest pain etc.

28. b) in smokers & some industrial workers respiratory mucosa is exposed to inhaled carbon & other toxic elements pseudostratified ciliated columnar epith . changes into stratified squamous epithelium ( squamous metaplasia ) 1 st step in the development of squamous cell carcinoma (main type of cancer of lung).