It is an organ whose main function is to produce sperms. In the testis, seminiferous tubules are surrounded by the interstitial tissue. In this tissue, there is a type of cell known after a scientist, Leydig. These cells of Leydig become activated by the luteinizing hormone from the pituitary gland and start synthesizing testosterone hormone. Testosterone is produced at the onset of puberty (age of sexual maturity). Testosterone helps in the development of secondary sexual characters in the male, for example, moustache, beard, etc.
In the ovary, there are a number of immature ova. One ovum is allowed to mature at a time. Each ovum is surrounded by follicle cells in a particular manner. When the ovum becomes mature and is about to be released, some of the associated cells secrete estrogen hormone. This hormone causes estrous (heat) and brings about changes in the female body, one of the changes being the development of breasts.
When the ovum is released (ovulation), the associated cells remain in the ovary and wait for a signal or news. If the news comes that the ovum has been fertilized and attached to the uterus (i.e., pregnancy has materialized), these cells becomes active. They begin to secrete two hormones, namely, progesterone and relaxin. These hormones bring about changes in the body of pregnant female. If there is no fertilization of ovum, these two hormones are not secreted.