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sperm

chromosomes determining genetic sex

SRY gene TDF(+) region

<— region determining gonadal sex gonad in indifferent stage sperm chromosomes determining genetic sex

SRY gene TDF(+) region

<— region determining gonadal sex gonad in indifferent stage

of fever) or if they fail to descend into the scrotum, sperm are not produced.

Each testis receives blood through a testicular artery, a direct branch of the abdominal aorta. It is highly convoluted near the testis, where it is surrounded by the pampiniform venous plexus, which carries blood from the testis to the abdominal veins. This arrangement allows heat exchange between the blood vessels and helps maintain the testes at a lower temperature. The cooler venous blood returning from the testis cools the arterial blood before it enters the testis through a countercurrent heat exchange mechanism. In addition, the cremaster muscle, whose fibers originate from the internal abdominal oblique muscle of the anterior abdominal wall, responds to changes in ambient temperature. Its contraction moves the testes closer to the abdominal wall, and its relaxation lowers the testes within the scrotum.

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