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What are the gonads and how do they arise?The male gonads are the testes, and the female gonads are the ovaries. In embryonic development, the gonads of both sexes develop within the abdominopelvic cavity. The developing gonadal tissue is found near the kidneys. But then, in developing male fetuses, a couple of months before birth, the testes begin to secrete the male sex hormone testosterone (note that the name of this hormone reflects the fact that it is made in the testes and that it is a steroid hormone). The presence of testosterone in the male causes the testes to descend from the abdominopelvic cavity toward their final destination-- the scrotum. How does this happen? Each testis (singular for testes) has a fibromuscular cord attached to it; this cord, called the gubernaculum, is attached at the other end to the skin of the future scrotum. The gubernacula (plural for gubernaculum) retract in the presence of testosterone. Because their firm point of attachment is in the inquinal region, the shortening of the gubernacula pull the testes downward. The gubernacula actually pass through the abdominal wall, and as they retract, they even pull the testes through the abdominal wall with them. The pathway through the abdominal wall has been called the inguinal canal, but I only mention this because your book does... In this manner, the testes end up down in the scrotum. In females, there is no testosterone present. The ovaries only descend a bit from their point of origin. In this manner, they end up within the pelvic cavity, attached to the lateral pelvic walls. What is the importance of the descent of the testes? The temperature in the scrotum is lower than the temperature within the abdominopelvic cavity. The cells that make the sperm (you will read about this on the sex cells web page), called germ cells, are highly sensitive to temperature. The germ cells will only produce sperm under the lower temperatures within the scrotum-- not under the higher temperatures of the abdominopelvic cavity. In fact, if exposed too long to the higher temperatures of the abdominopelvic cavity, the germ cells themselves will degenerate, and sperm will no longer be able to be made. |
© 2011 STCC Foundation Press |
