2010, Vol. 5 No. 2, Article 67

A Histo-anatomical Study of the Trachea of
Central Asian Tortoise (Testudo horsfieldii) in Iran

M. Shadkhast*, H. R. Shabazkia¹, A. S. Bigham², S. E. Shariati, T. Mahmoudi

Department of Anatomical and Histological Science of Basic Science,
Faculty of Veterinary Medicine, Sharekord University, Shahrekord, Iran

¹Department of Biochemistry and Pharmacology,
Faculty of Veterinary Medicine, Sharekord University, Shahrekord, Iran

²Departement of Veterinary Surgery and Radiology,
Faculty of Veterinary Medicine, Sharekord University, Shahrekord, Iran

*Corresponding Author; e-mail address: [email protected]

ABSTRACT

Histology of the tracheal epithelium has been studied in various species including reptiles like the common lizard (Lacerta agilis). However, meager information is available on this aspect in case of Asian tortoise (Testudo horsefieldii). A study was therefore conducted on (n=10) central Asian tortoise (five male and five female) to describe the microscopic structure of the tracheal wall. The observations revealed that trachea constituted mainly of complete cartilage rings lined by a respiratory epithelium (ciliated, basal and mucous cells) with variable morphology. The organ was short and divided into paired bronchi which remained separated along the sides of the neck.

KEY WORDS

Morphological study, tortoise, trachea.

INTRODUCTION

The structure of the epithelium of trachea has been widely studied in guinea-pig (Dalen, 1983), mouse ( Jeffery and Reid, 1975; Pack et al, 1981), rabbit (Plopper et al, 1984) and different reptilian species (Pastor et al, 1987; Tesik, 1987 & 1992). However, the structure and tracheal morphology of the central Asian tortoise has received little attention. The information available on this aspect is very scanty in reptiles and mainly refers to lizards and turtle (Tesik loc. cit. and Pastor et al loc.cit.). The present investigations was therefore undertaken to describe the microscopic structure of tracheal wall of the central Asian tortoise.

MATERIALS AND METHODS

The study was conducted on the trachea of (n=10) adult central Asian tortoise (five males and five females) at educational hospital of Faculty of the Veterinary Medicine, Sharekord University, Shahrekord, Iran. Tissue samples from the trachea were fixed by immersion in 10% buffered formalin. Samples were routinely processed and embedded in paraffin. Five micron thick sections were stained with haematoxylin and eosin, Van Giesson and Periodic acid Schiff (PAS).

RESULTS AND DISCUSSION

The observation revealed that a well defined trachea extended from end of pharynx nearly to the heart, where it bifurcated. The framework of thin tubular structure consisted of 60±1.2 superimposed complete rings of hyaline cartilage covered with loose connective tissue. Average length of the organ was 82 ±1.9mm (mean±SD) with inner lining consisting of a layer of epithelial tissue.
Light microscopic examination showed the trachea to be lined with a pseudostratified columnar epithelium that consisted of basal, ciliated and mucous cells. The basal cells were located in the basal portion of the epithelium and processes were occasionally observed passing towards the lumen. These cells were present in abundance and differentiated clearly.
The basal cells arise by multiple divisions similar to germinal cells of the epidermis (Blenkinsopp, 1967). Apparently the change of basal cell into the definitive type of the epithelial element occurs through an intermediate stage, represented by the intermediary cell. Presumably the whole process is completed so rapidly that the occurrence of intermediary cells in the epithelium becomes rare. Unlike basal cells, the intermediary cells are considerably less uniform. Their cytoplasm varies in density containing no secretory granules. In Testudo horsefieldii, the goblet and granular cells arising from intermediary cells retain the typical morphological traits that characterize them as specific separate species. In birds and mammals it is possible to encounter cells bearing concurrently some traits of both granular and goblet element. Ciliogenesis in intermediary cells of rats was observed by Jeffery and Reid (1975).
During the present investigation tracheal epithelium showed variations in thickness and stratification depending on the area, especially in the cartilaginous and epithelial part from the larynx to the extra pulmonary bronchi. However, no differences were observed between the cartilaginous and the membranous zones. These observations were not however in agreement with finding of Tesik (1984 & 1992) who reported abundant presence of granular cells in the tracheas of Lacerta vivipara and Lacerta agilis; and also found ciliated, granular and goblet cells frequently in the tracheal epithelium of most of the reptiles. Their mutual numerical proportions varied with the order or family of the reptiles examined. The incidence of occurrence of goblet and granular cells was governed by the law of reciprocity. In the present study few lymphocytes and plasma cells were observed in the lamina propria of tracheal bronchus whereas these cells are found in abundance in mammals (Dalen, 1983; Jeffery and Reid 1975; Pack et al 1981). The presence of well defined cartilaginous structures forming complete circles in most portions of the trachea, which gradually became segmented in its caudal region, indicates their importance in the maintenance of patency to air.
The trachea of Testudo horsefieldii was well defined, slightly different in structure from the trachea of reptiles studied so far and resembling the trachea of mammals except for presence of complete hyaline cartilage rings.

REFERENCES

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FIGURES

Fig.1-Dorsal view of Testudo horsefieldii (Central Asian Tortoise)

Fig. 2. Bifurcation of bronchials from trachea (white arrow)

Fig. 3. Transvers section of the trachea. Epithelial lining separated from the cartilage by loose connective tissue (Van Giessen 4X)

Fig. 4. Tracheal epithelium showing. Basal cell, ciliated and mucous cell (Van Giessen, 10X)

Fig. 5. Tracheal epithelium showing the goblet cells (white arrow), ciliated cells (yellow arrow) and basal cells (black arrow) (Van Giessen, 40X)

Fig. 6. Basal cell of tracheal epithelium - note the high vascularity of the connective tissue (Van Giessen, 40X)

Fig. 7. The laminal propria of trachea showing abundant lymphocyte and plasma cells (PAS, 40X)