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Journal of the Anatomical Society of India

Ductus Deferens-a Comparative Histology in Mammals

Author(s): Khan, Aijaz, A., Zaidi, M.T; Faruqi, N.A.

Vol. 52, No. 2 (2003-07 - 2003-12)

Department of Anatomy,J.N. Medical College,A.M.U. Aligarh, INDIA.

Abstract

The ductus deferens from laboratory animals is quite often used for teaching microscopic anatomy. The information about the comparative histology of mammalian ductus deferens is not adequate. The present study was undertaken to provide qualitative comparative features of ductus deferens among albino rat, rabbit, goat, buffalo and human. Samples of ductus deferens (2 to 5) from each animal were immersion fixed in 10% formalin. 8 to 10m thick paraffin sections stained with H & E were observed under light microscope. Both external and luminal diameters of human ductus deferens were found to be more than those in other animals. Longitudinal mucosal folds were found to be most numerous and complex in rabbit. Less prominent four longitudinal folds located at regular intervals were found to be characteristic feature of ductus deferens of goat and buffalo. Lining epithelium was found to be simple cuboidal and columnar in rabbit, low columnar pseudostratified in goat and buffalo, tall columnar poseudostratified in human and pseudostratified columnar ciliated (stereocilia) in rat. Tunica musculosa consisted of three laminae (less developed inner and outer longitudinal, and a well-developed middle circular) in human and rat. The inner longitudinal layer remained ill defined in goat, buffalo and rabbit. The middle circular remained most prominent in all except rabbit. The outer longitudinal layer in rabbit was most prominent and consisted of coarse bundles of smooth muscles. Tunica adventitia did not reveal definite species-specific characteristic feature but consisted of loose areolar tissue having rich blood supply. It was concluded that the ductus deferens from different mammals revealed some species-speciffic characteristics.

Key words: ductus deferens, vas deferens, vasectomy,

Introduction:

According to microanatomical description available in different textbooks (Bloom and Fawcett, 1984; Cormack, 1987; di Fiore, 1989; Donald and Gail, 1969; Garg et al, 1999; Geoffrey, 1960; Haider et al, 2002; Hasan, 1974; Janqueira, 1995; Krstic, 1991; Williams et al 1995; Young and Heath, 2000) the human vas deferens is a thick-walled muscular tube. It consists of from within outwards three tunics namely, tunica mucosa, tunica musculosa and tunica adventitia. It is said to lack distinct tunica submucosa (Husan et. al., 1974) Mucosal lining is described to have longitudinal folds resulting into irregular outline of its lumen. These folds are believed to allow for expansion during ejaculation (Young and Heath, 2000). The epithelium is columnar, nonciliated through most part and its distal part shows bilaminar columnar with superficial layer having stereocila (Williams et. al, 1995). Its pseudostratified epithelium may possess tuft of microvilli (stereocilia) similar to that of epididymis to absorb the excess fluid produced by the testis (Young and Heath, 2000). Tunica musculosa is three layered, i.e., an inner longitudinal layer, intermediate circular layer and an outer longitudinal layer. The thick smooth muscle coat by its peristaltic action is said to be responsible for its pumping action during ejaculation (Krstic, 1991). Tunica adventitia consists of richly vascularized, loose connective tissue merging with the surrounding connetive tissue of the spermatic cord. It provides nutritional support to the different tunics of the vas deferens. Slides of various organs used for teaching histology commonly belong to mammals other than human because of the inherent difficulty associated with the procurement of fresh human tissue for this purpose. Due to lack of literature on comparative anatomy, students get confused and find it difficult to correlate. This prompted us to study the comparative features of one of the functionally very important organ that is ductus deferens in different mammals.

Material and Methods:

Ductus deferens obtained from male albino rat, rabbit, goat, buffalo and human were immersion fixed in 10% formalin. Samples from two albino rats which were fixed by intracardiac perfusion method were also included in this study. Specimen of human ductus deferens were obtained during male sterilization (vasectomy). Tissue samples were processed for paraffin embedding and 8-10m thick sections were obtained. Observations were made on H & E stained sections under light microscope. Photomicrographs were taken under objectives of x 4 to x 40.

Observations:

In this qualitative study, it was found that the absolute value absolute value of the diamater of the human vas deferens is much more than those from other animals included in this study. Wall thickness was found to be almost equal to the diameter of lumen in rat and human (Fig 1A, 5A). The lumen was irregular in all species due to longitudinal fold of lamina propria and overlying epithelium. In human, the two forms of mucosal folds namely crests or papillae (di Fiore, 1989) were noticed (Fig. 5A). However, in goat and buffalo these folds were not prominent and less in number (commonly 4) and were placed at regular intervals (Fig. 3A, 4A). In rat, mucosal folds were very variable while the rabbit ductus deferens was characterized by plethora of complex mucosal folds (Fig. 2A). The epithelial lining presented variable shades among the species ranging from simple cuboidal and low columnar in rabbit (Fig. 3B) to columnar pseudostratified in others (Fig. IB, 3B, 4B, 5B). However, the stereocilia were noticed only in those samples of rat ductus deferens which were obtained from perfussion fixed rats (Fig. 1B). Tunica musculosa was prominent in all the species. However the characteristic trilaminar structure (inner and outer longitudinal layers and middle circular layer of smooth muscles) could be recognized only in rat (Fig. 1A) and human (Fig. 5A). In other species the inner longitudinal layer remained ill defined. In case of rabbit, only two layers could be identified, i.e. relatively less developed inner circular layer and well-developed outer longitudinal layer (Fig. 2A). The latter consisted of loosely aranged coarse fascicles of smooth muscles (Fig. 2B). The tunica adventitia appeared quite vascular in all species and consisted of loose connective tissue associated with nerves and lymphatics and it diffusely merged with the surrounding supportive tissue.

Discussion:

Human ductus deferens has been described as most heavily muscled tube in the body (Hasan et al, 1974) and possesses narrow (Cormack, 1987), irregular (di Foire, 1989) lumen. The ductus deferens of rat showed close resemblance with human with respect to its ratio of wall thickness to lumen diameter and also trilaminar tunica musculosa. The irregularity in the shape of lumen has been attributed to the longitudinal mucosal folds; and that in turn is believed to be the effect of contraction of smooth muscles in the tunica musculosa. Prominence and complexity of these folds in rabbit ductus deferens might be attributed either to prominent outer longitudinal muscle coat or poorly developed circular muscle coat (Fig. 2A, 2B). In the absence of definite submucosa these mucosal folds are believed to adjust for the expansion (probably by flattening) which is required during ejaculation. But how far the complexity of these mucosal foldings affect on the progression of semen, remains to be explained. Role of regular compartmentalization of the lumen, observed in goat (Fig. 3A) and buffalo (Fig. 4A) in facilitating the propulsion of intraluminal contents is also not well understood. Non-ciliated pseudostratified (short or tall) epithelium was observed to be common finding except the simple low columnar epithelium found in rabbit ductus deferens. Presence of stereocilia could not be satisfactorily demonstrated across the species, except in those samples obtained from perfusion fixed rats. From this it appears that the immersion fixation has probably failed to fix such delicate structures as stereocilia. Absence of stereocila along most of its extent has also been suggested (Williams et. al., 1995). Since ductus deferens is thought to require testicular hormone for its maturation (Hasan et. al., 1974), presence of sterocilia may be an expression of functional status of the testis. Although, different functional cell types viz, basal cells (Krstic, 1991), secretory columnar cells (Williams et. el., 1995) and with secretory granules in apical poles (Krstic, 1991) have been described. But routine H & E staining failed to identify such type of cells individually. According to Williams et. el. 1995 the three layers of tunica musculosa are intermingled, but others are of the opinion that some outer longitudinal layer penetrate into circular layer to reenter the outer longitudinal layer and thus making helically arranged muscle loops (Krstic, 1991). Though the 3-D structure of the arrangement of the muscle fibres is not fully understood, such kind of spiral loop arrangement is said to impart vas deferens a pumping action during forceful peristaltic action at the time of ejaculation (Krstic, 1991) Such explanation appears more plausible with the microstructure of rat and human vas deferens. However, it appears less likely in rabbit where outer longitudinal layer predominates and remains separated from poorly developed circular layer. Co-existance of such pattern of musculature with complex mucosal folds awaits better explanation. Ejaculation is a sympathetic phenomenon (Guyton and Hall, 2000. Each muscle cell of tunica musculosa is said to get nerve endings (Krstic, 1991) and this meets its functional requirement. Tunica adventitia remains primarily a supportive coat. It was concluded that the ductus deferens across the mammlian group revealed some common basic structure and at the same time it also presented some striking species-specific differences by which it could be identified individually. Microstructure of rabbit ductus deferens deserved further explaination on its mechanism of action.

References:

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Fig. 1 A

Photomicrograph of rat ductus deferens showing thick tunica musculosa. (H & E stain, X 40).(H & E stain, X 400).

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Fig I B

Photomicrograph of rat ductus deferens showing pseudostratified epithelium bearing stereocilia.

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Fig. 2A

Photomicrograph of rabbit ductus deferens showing complex mucosal folds, thin circular and thick outer longitudinal muscle coat. ( H & E stain, X 40).

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Fig. 2B

Photomicrograph of rabbit ductus deferens showing outer longitudinal inner circular muscle layer and cuboidal to low columnar epithelial cells. (H & E stain, X 400).

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Fig. 3A

Photomicrograph of goat ductus deferens showing four compartments of lumen. (H & E stain, X 40)

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Fig. 3 B

Photomicrograph of goat ductus deferens showing pseudostratified non-ciliated epithelium. (H & E stain, X 400).

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Fig. 4A

A Photomicrograph of buffalo ductus deferens showing four compartments of lumen. ( H & stain, X 40).

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Fig. 4B

Photomicrograph of buffalo ductus deferens showing poorly developed mucosal folds and pseudostratified nonciliated epithelium.(H & stain, X 400).

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Fig.5A

Photomicrograph of human ductus deferens showing thick muscle coat and irregular mucosal folds. (H & E stain, X 40).

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Fig. 5B

Photomicrograph of human ductus deferens showing a mucosal fold having nonciliated pseudostratified columnar epithelium. (H & E stain, X 400).

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