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vol.17 número1ESTUDIOS MESO Y MICROSCOPICO DE LA VENA FACIAL CON LOS TEJIDOS ADYACENTESARTERIA TIROIDEA SUPERIOR: ORIGEN, RAMAS COLATERALES Y GLANDULARES índice de autoresíndice de materiabúsqueda de artículos
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Revista chilena de anatomía

versión impresa ISSN 0716-9868

Rev. chil. anat. v.17 n.1 Temuco  1999

http://dx.doi.org/10.4067/S0716-98681999000100006 

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

Fig. 4. High magnification on the attachment (arrow) between vocal muscle (M) and arythenoid cartilage (*).
X 20
Fig. 5. Lamina propria of the larynx of chinchila. Shows elastic fibers (big arrow) and collagen fibers (small arrow). X 40


Scanning electron microscopy

Scanning electron microscopy images of the larynx delimits the supraglottic, glottic, infraglottic spaces, vestibular, vocal folds and the laryngeal ventricule (Fig. 6). The surface of the supraglottic space is covered predominantly with stratified epithelium; the superficial cells are protruded showing depressions between adjacent cells presenting the cobblestone appearance. Furthermore, ciliated cells scatter singly or in groups are observed among the numerous non-ciliated ones. The vestibular fold and the laryngeal ventricule are also lined by the stratified epithelium with cobblestone appearance (Fig. 7).

Fig. 6. Panoramic view of the larynx of chinchila. Shows vocal cord (*), vocal process of arythenoid cartilage (arrow), vestibular cord (**) and ventricule (V). X 60


The vocal fold is covered by stratified squamous epithelium without cornified layer. The polygonal epithelial cells showed distinct borders, flat surface and microridges (Fig. 8). Near to the caudal part of the vocal fold the epithelium gradually changes through the stratified squamous to the intermediated type (Fig.9). This epithelial surface demonstrated paving-stone appearance with depressions between adjacent cells. At higher magnification, the SEM images showed that these cells presented flat apical surface (Fig. 10). In the caudal luminal surface of the subglottis area, it may be seen a typical pseudostratified respiratory epithelium, composed by ciliated and non-ciliated cells with short microvilli (Fig. 11). The lamina propria of the larynx is composed by collagen and elastic fibers disposed in several directions constituting an intricated meshwork (Fig. 12).

Fig. 7. SEM view of the larynx. Note the supraglottis epithelium composed by ciliated (arrow) and non-ciliated cells (*). X 1600 Fig. 8. High magnification of the vocal cord epithelium. Shows polygonal cells, distinct borders (arrow) and microrigdes (small arrows). X 2600

Fig. 9. Transitional area from vocal cord to subglottic area. Note stratified squamous epithelium in the vocal cord (*) and intermediated epithelium in the subglottic area (**). X 1200
Fig. 10. High magnification of the intermediated epithelium. X 1600

Fig. 11. SEM view of the respiratory epithelium from subglottic area. Shows ciliated (arrow) and non-ciliated (*) cells. X 210
Fig. 12. Shows the lamina propria of the larynx formed by collagen and elastic fibers disposed in several directions. X 1800

DISCUSSION

The larynx of domestic animals presented the thyroid, arytenoid and epiglottic cartilages; dog and horse have cuneiformes cartilage while the cat do not has the corniculate one (SOLIS, 1976; SISSON et al. 1986).

The vocal muscle of Chinchilla showed rostral insertion on the internal surface of the thyroid and caudal insertion in the vocal process of the arythenoid cartilages being the medial portion of the thyroarytenoid muscle. Similar results were obtained in other species by NEGUS, SUÁREZ NIETO et al. (1986) and GUIDA. The human vocal muscle is frequently denominated the medial or internal part (par vocalis) of the thyroarytenoid muscle (NEGUS; GRAY, 1979; LATARJET & LIARD, 1989). On the other hand, another authors described it as a distinct muscle (GARDNER et al. 1988; HOLLINSHEAD & ROSSE, 1991). GRASSÉ (1968) reported that the thyroarytenoid muscle of rodents do not have internal or external parts; in horse this muscle frequently showed superior and inferior fascicles named respectively ventricular and vocal muscles. According to ANDRADE FILHO the vocal and the thyroarytenoid muscles of bovines belong to the same muscle mass with only a narrowing between them in the vocal ligament portion. These muscles appeared very thick due to the need for a strong fold contraction in the protection mechanism of the inferior aerial ducts which is the most important function in the rumination process of bovines. In the majority of carnivorous the thyroarytenoid muscle is simple in spite of being separated by two fascicles like in bears. The cat larynx has an primitive structure when compared with the dog: the thyroaytenoid muscle is unique connected with undeveloped vocal folds and the laryngeal ventricule is absent (SUÁREZ NIETO et al.).

The lateral walls of the larynx of Chinchilla possessed two pairs of mucosal folds denominated vestibular and vocal folds separeted by the laryngeal ventricule. The majority of mammals presented the same characteristics differing in the size of the laryngeal ventricule (BROCKMEYER et al.; NAKANO et al.; GUIDA and ANDRADE FILHO). However, some species like the mouse do not has laryngeal ventricule and the vestibular fold (NAKANO et al.).

Embrionically, the larynx is lined by ciliated columnar epithelium; latter some areas became stratified squamous (UCHIDA, 1961; ENDO, 1972). There are different epithelial types in the adult larynx (NAKANO,1986; NAKANO & MUTO,1986). Many researches decribed the epithelial layer of the transitional zone of the larynx using a multiplicity of terms that causes confusion. YAMADA named this important epithelial zone with the term transitional epithelium; HIRAKI (1976) reported as nonciliated columnar epithelium; LEWIS (1981) like pseudostratified cuboidal epithelium. On the other hand, the text-book of histology like GREEP (1966) classified the transitional epithelium as stratified columnar or ciliated one. NAKANO (1986) and NAKANO & MUTO (1986) described the presence of the intermediate epithelium on the transitional zone which exhibit gradations ranging from stratified squamous to ciliated columnar epithelium. We agreed with NAKANO (1986) with the term intermediate epithelium cause it summarized the epithelial variation on the different species.

Our results showed that the area between the vocal cord and the trachea presented some differents epithelial type. The rostral part of the vocal cord is lined by stratified squamous epithelium while the caudal part demonstrated the gradations from stratified squamous to ciliated columnar epithelium that appeared in trachea. The researches showed that transitional zone presented an epithelial layer which can be changed from specie to specie. NAKANO et al. observed that in the Suncus murinus, the epithelium of the supraglottic area has cobblestone appearance which extends to the vestibular fold. The vestibular fold also can show paving-stone appearance. The same observations occurred in the vocal fold that still demonstrated scattered ciliated cells. According to NAKANO (1986), regions where cartilages were close to the epithelial surface were lined by stratified squamous epithelium. Specifically in larynx, these areas are subjected to mechanical stress due to air flow or friction between epithelial surfaces. Another protection factor is the presence of microrigdes in the superficial cells cause keep more quantity of mucous between adjacent cells.

Scanning electron microscopic images demonstrated the original architecture of the connective tissue. In the last years several methodologies were developed and many papers analysed the differences between the lamina propria in many organs and species (NAKANO, 1992; MARTINEZ et al. 1995; 1998). The collagen and thick elastic fibers of the connective tissue of Chinchilla are important in the attachment of the vocal muscle to the thyroid and arythenoid cartilages.

ACKNOWLEDGEMENTS

We thank the Electron Microscopic Center of the State University of São Paulo, Botucatu / SP, Brazil.

 

RESUMEN: Realizamos un estudio sobre aspectos morfológicos de la laringe de la chinchilla. La laringe está compuesta por las porciones muscular, membranosa y cartilaginosa y tiene en promedio 9 mm de longitud. En la pared lateral se localizan los pliegues vocales y vestibulares; el ventrículo laríngeo es una pequeña depresión localizada entre estos pliegues. El epitelio laríngeo fue estudiado a través de la microscopía fotónica y electrónica de barrido.

La superficie del espacio supraglotico está cubierto predominantemente por epitelio estratificado con aspecto de adoquín, mientras que, puede observarse un típico epitelio seudoestratificado compuesto por células ciliadas y no ciliadas en el área de la subglotis. Sin embargo, cerca de la parte caudal del pliegue vocal el epitelio cambia gradualmente de escamoso estratificado al tipo intermedio demostrando un aspecto de guardacantón. La capa subepitelial estaba compuesta por fibras elásticas y colágenas que constituían una intrincada malla.

PALABRAS CLAVE: 1. Laringe; 2. Pliegues vocales; 3. Microscopía electrónica de barrido; 4. Chinchilla laniger.
* Departamento de Morfologia e Patologia, CCBS, Universidade Federal de São Carlos / SP (UFSCar), Brasil.
** Departamento de Anatomia, IB, Universidade Estadual Paulista - Botucatu / SP (UNESP), Brasil

 Dirección para correspondencia:
Prof. Dr. Marcelo Martinez
Laboratório de Anatomia
Departamento de Morfologia e Patologia
Universidade Federal de São Carlos
Rodovia Washington Luís Km 235 - CEP 13565905
Telefone 55-016-2608330 Fax: 55-016-2608326
São Carlos - SP -

Recibido : 17-12-1998
Aceptado: 10-05-1999

 

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