1. Histomorphological study of the trachea and lungs in male and female guinea pigs (Cavia porcellus)

2. Introduction
The domestic guinea pig Cavia porcellus (also Known as the cavy or cuy ),is a small ,stocky, tailless rodent commonly used in biomedical research. Guinea pigs are hystricomorphic rodents related to the porcupine and chinchilla. They are not at all closely related to swine. Guinea pigs originated in South America, where they are still of importance as a meat animal ,and have a role in religious ceremonies and local medicine .

3. They are still used in research ,primarily as models for human medical condition such as juvenile diabetes tuberculosis, scurvy ,and pregnancy complications .The biological characteristic of guinea pigs make these animals a valuable animal models for human medical conditions , for research in fields of biology medicine and immunology . the respiratory plays important role in olfaction ,phonation, regulation of body temperature .

4. The lower respiratory tract include the trachea , bronchi, bronchioles and the lungs .The structures of respiratory tract are varied among species and within each species . Trachea is a flexible tube composed of cartilaginous rings, connected by a fibromuscular membrane and lined internally by mucosa. It is composed of various of C-shaped tracheal cartilages in different species which are open dorsally and the space is bridged by tracheal muscle .

5. Materials and Methods
Ten healthy appearance male and female adult guinea pigs (Cavia porcellus ) were used for anatomical and histological study of trachea and lung, collected from the Al - Kindy company of Baghdad .
The 10 adult guinea pigs were divided in to three groups :
First group include 4( 2 male and 2 female ) used for anatomical study.
Second group include 4( 2 male and 2 female ) used for preparation cast to study of bronchial tree branching .
Third group include 2( 1 male and 1 female ) used for histological study. .

7. Results

8. Fig.1: Topographic and the gross anatomy of the trachea in male guinea pigs Show the . 1 – Trachea (cervical region) 2- Larynx.

9. Fig.2: Topographic and the gross anatomy of trachea in male guinea pigs. 1-Trachea (cervical region) .2-thoracic region 3- right primary bronchi . 4- Left primary bronchi. 5- Right lung. 6- Left lung.

10. Fig.3: Gross anatomy of the tracheal ring in cross section in female guinea pigs.

11. Fig.4: A- Right and B- Left lung in the thoracic cavity of male guinea pigs .

12. Fig. 5: Trachea and lung(dorsal view) in female guinea pigs Shows
Fig. 5: Trachea and lung(dorsal view) in female guinea pigs Shows .1- trachea. 2- Right principal bronchus. 3 –right apical lobe. 4 -right middle lobe.5- accessory lobe. 6 -right caudal lobe.7- left principal bronchus. 8-left apical lobe. 9 - left middle lobe.10-left caudal lobe.

13. Fig.6: Gross anatomy of trachea and lung (dorsal view) in female guinea pigs Shows. 1-trachea.2-right apical lobe.3-right caudal lobe.4-left apical lobe.5-left middle lobe.6-left caudal lobe .

14. Fig.7: The gross anatomy (ventral view) of lung in female guinea pigs Show .1-trachea. 2-Diphragmatic surface .

15. Fig. 8: Trachea and lungs(ventral views) of male guinea pigs Show the
Fig.8: Trachea and lungs(ventral views) of male guinea pigs Show the.1-trachea.2-apical lobe of right lung.3-middle lobe of right lung.4-caudal lobe of right lung.5-accessory lobe of right lung.6-apical lobe of left lung.7-middle lobe of left lung.8-caudal lobe of left lung .

16. Fig.9.A, B.. :The resin cast for the left bronchial tree which illustrated of the direction of the ramification of the bronchial tree.show1-Trachea.2-right principal bronchus.3-left principal bronchus.4- R. apical primary bronchi.5-R.Middle primary bronchi.6-R.Accessory primary bronchi.7-R.Caudal primary bronchi.8-L.Apical primary bronchi.9-L.Middle primary bronchi.10-L.Caudal primary bronchi .

17. Fig.10. The resin cast of bronchial tree illustrates the ramification of the bronchial, bronchioles branches and directions.Show.1-Trachea.2-Right principal bronchus.3-left principal bronchus.4-Primary bronchi.5-Secondary bronchi.6-Tertiary bronchi.7-Alveoli

18. Fig. 1:Histological section of trachea in male guinea pigs. 1-cilia
Fig.1:Histological section of trachea in male guinea pigs.1-cilia.2-epithelium (seudostratified columnar ciliated epithelium) .3-Tunica submucosa . 4-Hyaline cartilage.(HαE) stain (X 40) .

19. Fig.2: Histological section of trachea in female guinea pigs.
1-Cilia.2-Ciliated columnar epithelium. 3-Basal cell.5-Hyalin cartilage. HαE.stain (X 10).

20. Fig.3: Histologica section of trachea in male guinea pigs show.
1-Tunica mucosa .2- Goblet cells. 3 -Basal cell . 4- Lamina propra .5-Tunica submucosa .6- Hyaline cartilage. (PAS) stain (X40)

21. Fig.4: Histological section in trachea of male guinea pigs show.
1-Tunica mucosa.2-Muscularis mucosa.3-Tunica submucosa .4-Blood vessel.5-Hyalin cartilage.(PAS) stain (X 40).

22. Fig.5: Histological section in trachea of male guinea pigs show
1- the mucous tracheal glands (arrow) in the submucosa (PAS) stain (X400).

23. Fig.6:Histological section in trachea of male guinea pigs show .
1-Tunica submucosa .Perichondrium of hyaline cartilage .3-hyaline cartilage.4-Tunica adventitia. H α E.(X 40).

24. Fig.7:histological section of extra pulmonary bronchi in female guinea pigs show.1-muscularis mucosa.2-Tunica submucosa 3-submucosal gland.4-hyaline cartilage. 5-blood vessels (PAS) stain.(X100 ).

25. Conclusion

26. The histological of trachea and lung were similar in male and female guinea pigs .
The shape of tracheal rings are semi-circular in cross section and the trachealis muscle attached to the inner surface of the cartilaginous rings.

27. The tracheal wall consist of four tunics ,tunica mucosa ,tunica submucosa, musculocartilaginous and tunica adventitia.
The mucosa of trachea is lined by pseudostratified ciliated columnar epithelium with goblet cells which give a positive reaction for periodic acid schift(PAS).
The Extra pulmonary bronchi were similar in histological structure to the trachea.