Testicular Development And Descent

The embryonic gonad has the potential to become either a testis or an ovary. After gonadal differentiation, testes remain in the abdominal cavity until they descend into the scrotum. In cattle and sheep, testicular descent occurs in midgestation and descent occurs in late gestation in swine and horses. In contrast, testicular descent occurs postna-tally in rabbits and dogs. Avian testes remain in the body cavity attached to the wall of the kidney, and the testes function at body temperature. Cryptorchidism, the retention of one or both testes in the abdominal cavity, is inherited. In most domestic mammals, the normal temperature of the testes is several degrees cooler in the scrotum compared with body temperature. The cooler environment is essential for sperm production and bilateral cryptorchid males are sterile. Temperature regulation of the testes is controlled by muscular regulation (cremaster muscle) of the distance that the testes is from the body, heat transfer from arterial blood going to the testes to cooler venous blood from the testes to reduce the temperature of testicular arterial blood, and changes in scrotal surface area and sweating.

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