Tanyel F Cahit
Department of Pediatric Surgery, Hacettepe University, Faculty of Medicine, Ankara, Turkey.
Turk J Pediatr. 2004;46 Suppl:18-27.
The testis is descended through the processus vaginalis via propulsive force generated by the muscles derived from the gubernaculum. After propelling the testis, the smooth muscle should undergo programmed cell death for obliteration of the processus vaginalis. Achievement of programmed cell death mandates a transient decrease in sympathetic, but an increase in parasympathetic, tonuses. Since the sympathetic tonus is androgen-dependent, the decrease in androgen levels during the third trimester appears to be responsible for the process. Alterations in timing, intensity or duration of the decrease in sympathetic tonus under the control of the central nervous system give rise to hernia, hydrocele or abnormal testis localizations. The persistence of decrease causes undescended, retracted, or ascended testis. Absence or inadequacy of the decrease in sympathetic tonus results in rescue of more smooth muscle, thus inhibiting the obliteration. Inadequacy in the intensity or duration rescues less smooth muscle and gives rise to a hydrocele. Persistence of signals towards inducing programmed cell death contributes to decrease in fertility, and provides a basis for epididymo-vasal anomalies. The reduction in the central regulatory mechanism that involves catecholaminergic activity explains the blunting of luteinizing hormone (LH) response to gonadotropin-releasing hormone (GnRH). The explained mechanism precisely defines the role of all factors, and links all of the associations related to the process of descent.
睾丸通过由睾丸引带衍生的肌肉产生的推进力,经鞘突下降。在推动睾丸下降后,平滑肌应经历程序性细胞死亡,以使鞘突闭塞。程序性细胞死亡的实现要求交感神经张力短暂降低,而副交感神经张力增加。由于交感神经张力依赖雄激素,孕晚期雄激素水平下降似乎是该过程的原因。在中枢神经系统控制下,交感神经张力降低的时间、强度或持续时间发生改变,会导致疝气、鞘膜积液或睾丸位置异常。交感神经张力持续降低会导致睾丸未降、回缩或上升。交感神经张力降低缺失或不足会使更多平滑肌得以保留,从而抑制鞘突闭塞。强度或持续时间不足会使较少的平滑肌得以保留,进而导致鞘膜积液。诱导程序性细胞死亡的信号持续存在会导致生育能力下降,并为附睾输精管异常提供了基础。涉及儿茶酚胺能活性的中枢调节机制的减弱解释了黄体生成素(LH)对促性腺激素释放激素(GnRH)反应的迟钝。所解释的机制精确地界定了所有因素的作用,并将与下降过程相关的所有关联联系起来。