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Revista chilena de anatomía
versión impresa ISSN 0716-9868
Rev. chil. anat. v.17 n.1 Temuco 1999
MORPHOLOGICAL STUDY OF THE LARYNX OF CHINCHILLA (Chinchilla laniger)
ESTUDIO MORFOLOGICO DE LA LARINGE DE LA CHINCHILLA (Chinchilla laniger)
* Marcelo Martinez ** Heraldo Lorena Guida ** Robson J. S. Domingues ** Fernando D. Cassel ** Eládio Pessoa de A. Filho ** Francisco E. Martinez SUMMARY: The study was undertaken to collect data on morphological features of the larynx of the chinchilla. This larynx is composed by cartilaginous, membranous and muscular portions and has 9 mm of medium lenght. In the lateral wall there are the vestibular and vocal folds; the laryngeal ventricle are present in the region between the vestibular and vocal folds consisting in a moderate depression. The laryngeal epithelium was studied by light and scanning microscopic methods: the surface of the supraglottic space is covered predominantly by stratified epithelium with cobblestone appearance while it may be seen a typical pseudostratified epithelium composed by ciliated and non-ciliated cells on the subglottis area. However, near to the caudal part of the vocal fold the epithelium gradually changes through the stratified squamous to the intermediated type demonstrating paving-stone appearance.The subepithelial layer was composed by elastic and collagen fibers constituting an intricated meshwork. KEY WORDS: 1. Larynx; 2. Vocal cord; 3. Scanning electron microscopy; 4.Chinchilla laniger. INTRODUCTION Chinchillas are rodents from the Andes mountains that belong to Chinchilidae family. There are three species described: C. real, C. brevicaudata and C. laniger (MERÇON,1979). This last one shows high comercial value due to their skin. However, few papers are related to the anatomy and histology of this mammal in the literature (MARTINEZ et al. 1994). Larynx is an essential organ of respiratory tract which has the function, and one of the oldest according to phylogenetic, to close and open the glottis aiming at an effective protection against different bodies (NEGUS,1949). The vocal cords have an important role in several functions like respiratory, phonation and sphincteric action. The epithelial layer of the vocal cords protects the respiratory tract from inhaled particles and drying (BASTERRA et al., 1988). Several investigators described the topographic anatomy of the larynx (JOSEPHSON, 1926; SONESSON, 1960; GANZ, 1971; NAKAI et al. 1991; SATO et al. 1995; TAKAHASHI & YORIFUJI, 1997; GUIDA, 1997; ANDRADE FILHO, 1997). There are many available publications on the respiratory system epithelium, specifically in the larynx (NAKANO et al. 1989; BROCKMEYER et al. 1989; NAKANO & MUTO, 1990; KOITSCHEV et al. 1995). The intermediate epithelium consists of the transitional area between stratified squamous and ciliated columnar epithelium (NAKANO, 1986; NAKANO & MUTO, 1988; 1990). The majority of laryngeal carcinoma arises from the respiratory epithelium (YAMADA, 1976). Other important clinical aspects are the tobacco smoke and the air pollution increases. The present paper reported the anatomical, histological and ultrastructural features of the Chinchilla larynx and compared it with other species of rodents and mammals. MATERIAL AND METHOD A total of six adult Chinchillas (Chinchilla laniger) of both sexes were used in this study. The animals were sacrificed with ethilic-ether and then their laryngeal regions were removed and cut sagittaly. For light microscopy, three larynx were fixed in Bouin´s solution for 24h at room temperature, dehydrated in a graded ethanol and embedded in parafin routinely. Transversal sections of 7 micrometers thickness were stained with H.E and Weight Van-Gieson. For scanning electron microscopy, 3 larynx were fixed in modified Karnovsky”s fixative containing 2.5% glutaraldehyde, 2% paraformaldehyde in 0.1 M phosphate buffer pH 7.4 overnight at 4°C. Then, the samples were postfixed with 1% osmium tetroxide solution for 2h at 4°C and immersed in 2% Tannic acid. Subsequently, the specimens were dehydrated in graded ethanol, dried in a critical point drier Balzers CPD – 010, mounted in metal stubs and coated in ion coater Balzer MED – 010. The specimens were examined in a Philips FEM – 515 scanning electron microscope at 15 Kv. RESULTS Anatomy and Light microscopy The larynx of Chinchilla is composed by cartilaginous, membranous and muscular portions and has 9 mm of medium lenght. Upper view from the larynx showed the vestibular and vocal folds, glottis space, epiglottic and thyroid cartilages. The glottis space is posteriorly limited by the arythenoid and cuneiformes cartilage. Posterior view demonstrated the superior cornu of the thyroid cartilage which is the lateral limit of the larynx. In the sagittal section the three laryngeal spaces denominated supraglottic, glottic and infraglottic can be noted. The supraglottic space extends from the epiglotic cartilage to the vestibular fold; the glottic is limited by laryngeal ventricule and vocal fold while the subglottic forms the transitional area between the lower part of the larynx and the trachea. In the lateral wall there are the vestibular and vocal folds; the laryngeal ventricles are present in the region between the vestibular and vocal folds consisting in a moderate depression (Fig. 1).
Fig. 1. Macroscopic view of the larynx of chinchila. The sagital section shows the arythenoid (*), thyroid (T), cricoid (C), cuneiform (small arrow) and epiglottis (arrow) cartilages. Note the vocal cord (VC), glottis area (G), vestibular cord (VB), supraglottic space (S), infraglottic space (I) and tracheal cartilage (TR). X 8
The vocal muscle showed ventral insertion in the internal angle of the thyroid cartilage running almost parallel to the dorsal insertion in the vocal process of the arythenoid cartilage (Figs. 2, 3, 4). It can be considered as the medial part of the thyroarytenoid muscle. The vocal folds consisted of the mucosa and the vocalis muscle. Histologically, the mucosa is compposed by stratified squamous epithelium and lamina propria formed predominantly by collagen and elastic fibers. Laryngeal glands are observed constituted by submucosal acinis (Fig. 2,5).
|Fig. 2. Horizontal section on the glottis area. Shows vocal muscle (M), lamina propria (L), submucous glands (G), epithelial layer (small arrow) and anterior insertion of the vocal muscle in the thyroid cartilage (big arrow). X 10||Fig. 3. Shows the posterior insertion of the vocal muscle (M) in the arythenoid cartilage (*). X 10|
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