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Revista chilena de anatomía

versión impresa ISSN 0716-9868

Rev. chil. anat. v.19 n.2 Temuco ago. 2001 

IN THE DOG (Canis familiaris, L.)

EN EL PERRO (Canis familiaris, L.)

* Bruno Cesar Schimming; **Carlos Alberto Vicentini & ***Antônio Marcos Orsi

*** Laboratory of Anatomy, Faculty of Health Sciences, University of Marília, UNIMAR, Marília, SP, Brasil.
*** Department of Biological Sciences, Faculty of Sciences, UNESP, Bauru, SP, Brasil.
*** Department of Anatomy, Institute of Biosciences, UNESP, Botucatu, SP, Brasil.

SUMMARY:  The ductus epididymidis of the dog is lined by a pseudostratified columnar epithelium. The boundary tissue of the epididymis, surrounds the epithelium, and is divided into periductal stroma and tubular interstitium. Principal cells were observed in the luminal surface of the epithelium. Numerous stereocilia lined the luminal surface of principal cells. These results are compared with previous findings observed in the epididymis of other species.

  KEY WORDS: 1. Epididymis; 2. Dog; 3. Scanning electron microscopy.


       The epididymis is essential for normal reproduction of eutherian mammals because sperm leaving the testis are incapable of fertilizing the oocytes (Amann et al., 1993). Testicular sperm lack motility and fertility, but they acquire these abilities by the time they reach the tail of the epididymis (Bedford, 1975 and Goyal & Williams, 1991). The acquisition of these abilities by sperm depends upon their passage through a specific environment, which in turn is regulated by the absorptive and secretory activities of the epithelium lining the excurrent ducts of the testis (Turner et al., 1979). Information about the epididymis, especially in the rat, and changes that occur in sperm during their passage through the epididymis have been reviewed (Amann, 1987; Robaire & Hermo, 1988; Bedford & Hoskins, 1990; Hamilton, 1990 and Andonian & Hermo, 1999).

         The mammalian ductus epididymidis is lined by a pseudostratified epithelium and different cell types have been described in its epithelium in various species (Hamilton, 1975 and Robaire & Hermo). These cells have been presumed to have different functions (Glover & Nicander, 1971 and Robaire & Hermo). However, their interrelationships have not been thoroughly studied and are only incompletely understood (Arrighi et al., 1993).

       The main epididymal cell type is the principal cell, which is  columnar in form, displaying slender microvilli and abundant lysosomes (Hamilton, 1975 and Robaire & Hermo). Morphological and functional differences in principal cells along the epididymis have been reported in many mammalian species (Ramos & Dym, 1977; Jones et al., 1979; Connell & Donjacour, 1985; Robaire & Hermo and Palacios et al., 1993). These regional differences have been related with spermatozoa changes in sperm motility and fertilizing ability during their passage throughout the epididymis (Cooper, 1990).

         Epididymal structure has been examined in various mammals (Hamilton, 1975; Ramos & Dym; Robaire & Hermo; Goyal & Williams and Schimming et al., 1997). However, there were only few reports concerning the scanning electron microscopy (SEM) of mammalian epididymidis and with regard to dog species there no were at SEM study. This paper describe the structure of the dog epididymidis using SEM, and comparisions with previous studies were made.


         Fragments of the initial, middle and terminal segments of the epididymis were obtained from five sexually mature mongrel dogs (Canis familiaris, L.). The tissue samples were fixed by immersion in a formaldehyde-glutaraldehyde mixture in 0.1 M sodium-phosphate buffer at pH 7.2, at 4°C, 24 h. These fragments were washed in the buffer, post-fixed in 1% osmium tetroxide in 0.1 M sodium-phosphate buffer, and immersed in 2% tannic acid, during 90 minutes (Murakami, 1974). The tissues were dehydrated with ethanol, immersed in uranyl acetate and taken to the critical point drier with liquid carbon dioxide (Balzers, CPD-010, Germany). The material were sputtered with gold (Balzers MED-010, Germany), and the colloidal samples were analyzed in a Philips SEM-515 microscope (Philips, Netherlands) at 20 kV.


         The ductus epididymidis of the dog is formed by a single, highly convoluted duct (Fig. 1). The epididymis is covered with a tough layer of fibrous tissue, the tunica albuginea, which is structurally uniform in all epididymal segments (Fig. 2). The albuginea take origin to septa which divide the epididymal parenchyma in a non regular form resembling lobules. It is possible to define three major morphofunctional zones of the duct: initial, middle and terminal segments. 

The ductus epididymidis is lined by a pseudostratified epithelium which lays on the evident basement membrane. At high magnification, the basement membrane sets the limit between the epithelium and the tissues that surrounds the duct, e.g., the boundary tissue of the epididymis. The boundary tissue is divided into periductal stroma and tubular interstitium. The periductal stroma is the tissue located beneath the basement membra-ne and the tubular interstitium surrounds the intimal periductal stroma (Figs. 3 and 4).

Fig. 1. Dog epididymidis showing high convolutions (arrowheads). x 222.

Fig. 2. Scanning electron micrograph showing tunica albuginea (ta) and cross-section of the ductus epididymidis (arrowheads). x 31.

Fig. 3. Epithelium lining (stars), periductal stroma (asterisks) and tubular interstitium (rose) are viewed in the epididymidis of the dog. x 90.

Fig. 4. High magnification of figure 3, showing the epithelium lining (star), periductal stroma (asterisks), tubular interstitium (rose) and lumen (lu). x 222.
Fig. 5. The spermatozoa (arrow) are viewed in the epididymal lumen. x 777.

                  The principal cells were observed near the luminal surface and principal cell structure was basically similar throughout the epididymis. They display apical slender microvilli, as luminal projec-tions of the apical cell surface, which were tall but irregular and branched in the initial segment. Conversely, stereo-cilia which lined the luminal surface of principal cells in the terminal segment did not branch. They were shorter and denser and were regular in height, forming a low brush border of microvilli. This border was closely packed having uniform diameter, and contained fine filaments which extend from some distance into the apical cytoplasm of the cell (Figs. 6, 7 and 8). In the present study were observed sperma-tozoa into the lumen between the microvilli (Fig. 5).

Figs. 6, 7 and 8. Scanning electron micrographs of the luminal border of the principal cells showing branching of stereocilia.

Fig. 6. Initial segment, x 926.

Fig. 7. Middle segment, x 652.

Fig. 8. Terminal segment, x 576.


        According to Turner (1979), the epididymis is a single, highly convoluted tubule that links the efferent ducts of the testis to the vas deferens, as was seen in dog epididymidis. The epididymal tissue is made up of two major compartments: the epithelium and the lumen (Robaire & Hermo and Robaire & Viger, 1995). The epididymal duct of the dog is covered by a tunica albuginea which forms the septa that in turn divide the parenchyma of the organ, similarly as was described in Landrace pigs (Orsi et al., 1985).

         The epididymal boundary tissue is divided into periductal stroma and tubular interstitium. Viotto & Orsi (1989) denominated as lamina propria the periductal stroma of the cat epididymidis. The epididymal lumen contains  spermatozoa and fluid whose composition is constantly changed as the fluid moves from the initial to the terminal segment (Robaire & Viger). Similar observations were showed in the dog epididymidis.

         The epididymal duct is lined by a pseudostratified columnar epithelium, that has four major cell types: principal, basal, clear and halo cells (Robaire & Hermo). Goyal (1985) reported that the epithelium of all regions of the bovine epididymidis contained some cell types such as: principal, basal, and few apical epithelial cells, intraepithelial lymphocytes and macrophages. Other cell types as clear cells were observed in rat (Hamilton, 1975), hamster (Flickinger et al., 1978); and rabbit (Jones et al., 1979).

         All the morphological observations on the epididymal epithelium in dog have revealed clear similarities between it and other mammals (Hamilton, 1975 and Flickinger et al), mainly with the large domestic mammals (Sinowatz et al., 1981; Goyal; Goyal & Williams and Arrighi et al., 1993). Basically, principal cells were observed in the luminal surface of the dog epididymidis. Goyal & Williams have suggested that principal cells are the major cell type of the epithelium in goat epididymidis, and they are tall, and cylindrical cells, which extend from the basal lamina to the lumen.

         Stereocilia of various lengths and structural complexity have been previously identified as common projections of the apical surface of principal cells in the epididymis (Hoffer et al., 1973; Hamilton, 1975; Jones et al., 1984 and Taggart & Temple-Smith, 1989). A reduction in the length of stereocilia in the terminal segment had been described in some marsupials (Cummins et al., 1986 and Taggart & Temple-Smith), and in large domestic animals (Goyal & Williams). Stereocilia are replaced by a low brush border of microvilli in the terminal segment of the dog epididymidis (Schimming et al.). The microvilli brush border was also observed in principal cells of dasyurid marsupials (Taggart & Temple-Smith). The functional significance of the brush border is unclear but probably it convey the luminal content forward as discussed in efferent ductules of isogenic mice (Orsi et al., 1998). Principal cells have a large number of mitochondria scattered throughout the cytoplasm and numerous canaliculi and coated vesicles are present in the apical cytoplasm suggesting that the epididymidis terminal segment in addition to provid structural stability, may also have an absorptive function (Robaire & Hermo and Taggart & Temple-Smith).

ACKNOWLEDGMENT: The authors thank the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, Proc. 141512/95-4), for the partial support of this work, and the Electron Microscopy Center of UNESP at Botucatu (SP, Brasil), for technical assistance.

RESUMEN: El epidídimo en el perro está revestido por epitelio de tipo columnar pseudoestratificado, encontrándose el tejido conjuntivo inmediatamente debajo de él. El tejido conjuntivo epididimario consiste de estroma e intersticio. Fueron observadas células epiteliales con microvellosidades en el lumen del conducto. Se comparan los resultados obtenidos con los reportados por diversos autores ens otros mamíferos.

  PALABRAS CLAVE: 1. Epidídimo; 2. Perro; 3. Microscopía eletrónica de barrido.

Correspondence to:

Prof. Dr. Bruno Cesar Schimming
Laboratory of Anatomy
Faculty of Health Sciences
University of Marília - UNIMAR
Av. Hygino Muzzy Filho, 1001
Marília _ São Paulo
Cep 17525-902


Recibido : 16-04-2001
Aceptado: 29-05-2001


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