TAILIEUCHUNG - Encyclopedia Of Animal Science - M

Từ điển khoa học động vật vần N | Male Reproduction Physiological Comparisons Robert P. Wettemann Oklahoma State University Stillwater Oklahoma . INTRODUCTION Sperm production by the testes is a continuous process after puberty. Accessory glands are stimulated by male hormones and secretions of the glands compose most of the volume of semen. Size of the testes number of sperm produced each day volume of ejaculum and methods to store semen for artificial insemination vary among species. Increased testicular temperatures can reduce sperm production and cause reduced fertility or infertility. This temporary reduction in fertility exists until testicular tissues return to normal and there is sufficient time for the formation and maturation of a new cycle of sperm production. 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. TESTICULAR FUNCTIONS Testes have two major functions .

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