The descent of testis and reason for failed descent.

Although an enormous number of theories have been proposed to explain the descent of testis, none has provided a satisfactory explanation that covers the whole spectrum. Recent evidence suggests a hitherto unrecognized mechanism. This novel explanation precisely defihes all of the factors proven to be involved in the process, and links the features associated with normal or failed descent. The gubernaculum gives rise to both smooth and striated muscles. The testis is descended through the processus vaginalis via the propulsive force generated by the muscles. Propulsion describes the risk of torsion. Failure in descent in associated with a diminution in smooth muscle content, and a decrease in sympathetic tonus that depends on androgens. Alterations in G-protein linked signaling due to differences in primary messengers resulting from changes in sympathetic and parasympathetic tonuses provide the basis for blunting of testosterone response to human chorionic gonadotropin (hCG) and the decrease in fertility, but also for the increase in the risk of malignancy.