Final answer:
Luteinizing hormone (LH) is responsible for the rupture of an ovarian follicle and the release of a mature egg from an ovary. This hormone spikes just prior to the middle of the menstrual cycle, causing the most mature follicle to rupture and release its egg. The level of estrogen decreases when the other follicles degenerate.
Step-by-step explanation:
The hormone responsible for the rupture of an ovarian follicle and the release of a mature egg from an ovary is Luteinizing hormone (LH).
Just prior to the middle of the menstrual cycle, the level of estrogen increases and causes LH to rise rapidly. The spike in LH triggers ovulation, causing the most mature follicle to rupture and release its egg.
The level of estrogen decreases when the other follicles degenerate, preventing further development of eggs and follicles.