Mechanism Of Testicular Descent Research Articles

The known and unknown about the testicular descent and undescended testes

The mechanism of testicular descent in development of testis in embryonic period is very complex, and undescended testes(cryptorchidism) is a very common anomaly of the male genitalia.As it is close relatively with the later impaired fertility and cancer risk, involving reproduction, development, endocrinology and psychology, et al, the explorations of the mechanisms of testicular descent are continuing, and the studies on undescended testes such as the exact cause, pathogenesis, proper strategies for diagnosis and treatment are in progress.Along with some muddle becoming clear, the new puzzles often emerged.Perhaps this is getting closer to the truth.This paper is basically outlining the current research situation from the known and unknown aspects. Key words: Testicular descent; Undescended testes; Child

What Animal Models of Testicular Descent and Germ Cell Maturation Tell Us about the Mechanism in Humans.

Testicular descent occurs in most mammals in two main steps that have different hormonal control and anatomical processes. The evolution of testicular descent reveals the same basic processes in humans and animals, with minor differences in timing and anatomy, especially the location of the scrotum and the processus vaginalis. Animal models are useful as they reveal some embryological processes that cannot be studies easily in humans, such as the potential role of the mammary line and the role of the genitofemoral nerve. Postnatal germ cell development is very similar in animal models and humans, except for the timing of arrival of the testis into the scrotum, which is before birth in humans versus around puberty in rodents. Once all the minor differences between animal models and humans are taken into account, animal experimentation has provided amazing insights into the mechanisms of testicular descent, and recently, how the postnatal germ cell develops in normally descended and undescended testes.

Embryology of Undescended Testis and Mechanisms of Testicular Descent

Embryology of Undescended Testis and Mechanisms of Testicular Descent

The development and closure of the processus vaginalis

It is now well known that the failure of the processus vaginalis (PV) to close off following descent of the testis not only accounts for nearly all inguinal hernias of childhood [Rothenberg et al, 1953], but also for other common congenital conditions of childhood such as scrotal hydroceles and encysted hydroceles of the cord. Despite the direct relationship of the PV to these conditions and its intimate association with the mechanism of testicular descent, surprisingly little is known about this important structure. It is not known, for instance, how the PV develops, what precise role it plays in testicular descent, what makes it close, or exactly when it closes. The purpose of this paper is to review the past and present literature on the PV, examining specifically its role in testicular descent, its postulated modes of development, and the mechanisms of its closure and disappearence following descent of the testis.

Does the gubernaculum migrate during inguinoscrotal testicular descent in the rat?

The role of the gubernaculum in descent of the testis is controversial. The mechanism of testicular descent has been studied in the rat, because inguino-scrotal descent occurs postnatally in this species. Several authors have claimed that the cremasteric sac forms by eversion of the gubernacular cone, whereby regression of the extra-abdominal part of the gubernaculum creates a space into which the gubernacular cone everts to form the processus vaginalis within the scrotum. This postulated lack of any gubernacular migration phase contrasts with the situation in the human, where gubernacular migration appears to be an integral component of testicular descent. This study was designed to determine in the rat whether there is any gubernacular migration toward the scrotum during testicular descent, or whether eversion of the cremasteric sac alone could account for the extension of this sac into the bottom of the scrotum. Oblique sagittal sections of the inguino-perineal region were taken from rats aged 21 days of gestation and days 1, 3, 4, 6, 8, and 10 days postnatally. Histological sections were examined and the following measurements were obtained: gubernacular cone height, gubernaculum-scrotum distance, processus vaginalis length, and pubic symphysis-anus distance. The gubernaculum was not in close proximity to the developing scrotum at any age. After 21 days of gestation, there was little evidence of a substantial gubernacular bulb distal to the processus vaginalis. At all ages the gubernacular cone height was significantly less than the distance from the gubernaculum to the scrotum. These results show that the gubernaculum does not develop in close proximity to the developing scrotum. Even if complete eversion of the gubernaculum takes place, the gubernaculum would still fail to reach the bottom of the scrotum. It is proposed that gubernacular eversion is more apparent than real and that some degree of gubernacular migration is needed for complete extension of the cremasteric sac to the bottom of the scrotum.

Lack of Feminization of the Cremaster Nucleus in Cryptorchid Androgen Insensitive Rats

Androgens may control rat testicular descent via effects on the genitofemoral nerve or cranial gonadal ligaments. Androgen-mediated release of calcitonin gene-related peptide from the genitofemoral nerve (whose motoneuron cell bodies reside in the sexually dimorphic cremaster nucleus) may stimulate cremaster sac formation and testicular descent. Alternatively, androgens may cause regression of cranial gonadal ligaments and thereby allow the testes to descend. To evaluate these theories testicular position, and the cremaster sac and nucleus were studied in Tfm (androgen insensitive) rats. Testes were abdominal, inguinal and scrotal in 20%, 67% and 13% of Tfm male rats, respectively, and cranial ligaments were present in all cases. Mean cremaster nucleus motoneuron number was lower in female rats (70 ± 14) but not significantly different between normal male (256 ± 44) and Tfm male (231 ± 42) rats, and it correlated poorly with testicular position. Calcitonin gene-related peptide immunoreactivity was rarely observed in cremaster motoneurons. These data suggest that the cremaster nucleus is not androgen-dependent, calcitonin gene-related peptide release from cremaster motoneurons is not the likely mechanism of testicular descent and persistent cranial ligaments may cause cryptorchidism in the Tfm rat.

Abdominal Wall Defects and Cryoptorchidism: An Animal Model

Intra-abdominal pressure has been implicated in the mechanism of testicular descent. Boys born with abdominal wall defects reportedly have an increased incidence of cryptorchidism. To examine this relationship further a rat model was developed. The rat testis normally descends postnatally on or about day 21. In this study newborn male rats underwent surgical excision of all anterior abdominal musculature from the umbilicus to the xiphoid, while a control group had a sham procedure. In both groups steel wire was inserted into both testes as radiological markers to monitor descent. Animals were explored on day 28 to confirm the position of the testes. A total of 36 animals survived all sections of the protocol. Eight animals had adhesions and were dropped from the study. The results of 17 rats in the experimental group and 11 in the control group revealed that the surgically created abdominal wall defect did not result in cryptorchidism. This finding suggests that an intact anterior abdominal wall is not a prerequisite for testicular descent in the rat. (J. Urol, part 2, 140:1141-1144, 1988)

The mechanisms of testicular descent.

The mechanisms of testicular descent.

Hormonal regulation of testicular descent.

The involvement of testosterone in testicular descent and the mechanism of testicular descent were analyzed and discussed.

Testicular descent in the rat and a comparison of this process in the rat with that in the pig

Testicular descent in mammals with a saclike cremaster muscle and in those with a striplike cremaster muscle differs morphologically as well as topographically. In spite of this, functional interpretations are sometimes extrapolated from species to species without defining precisely the different structures involved in this process. This has resulted in several unnecessary conflicting opinions on the mechanism of testicular descent. In this study the anatomical changes of the structures involved in the process of testicular descent in the rat are described and these data are compared with similar data on the pig. It appears that the major changes in the process in both species are 1) the outgrowth of gubernacular mesenchyme, 2) subsequent regression of this mesenchyme, and 3) development and growth of the cremaster muscle. If the structures involved are properly defined the homology of the changes in both species becomes evident.

Mechanism of testicular descent

Mechanism of testicular descent