The menstrual cycle occurs in the uterus and ovary as part of possible sexual reproduction. The menstrual cycle occurs monthly and occurs so that the ovary can produce eggs and the uterus can prepare for fertilization of an egg. (Wikipedia) The menstrual cycle is a complex cycle and is controlled by hormones produced by many different glands. The hypothalamus causes the pituitary gland to produce chemicals that then cause the ovaries to produce the sex hormones estrogen and progesterone. Each gland and structure is affected by the activity of another which is biofeedback. The menstrual cycle is assumed to last approximately 28 days and occurs in four stages: the menstrual phase (days 1-5), the follicular phase (days 1-13), the ovulation phase (day 14), and the luteal phase. (days 15-13). 28). The countdown of the days of the menstrual cycle begins on the first day blood comes out of the vagina. (Women's Health) Puberty is the time in a person's life when the body begins to mature sexually; The hormone estrodiol is produced by women. Puberty is initiated by hormonal signals which go to the brain then to the gonads and ovaries in women. (NHS Choices Puberty) A hormone is produced by the gonads that stimulates the growth, function and change of the brain, skin, hormones, breast and sexual organs. During puberty it causes different changes, the physical changes are breast development, pubic hair, body shape (hips widen), vagina and uterus, menstruation and body odor. (Wikipedia)The first phase, the menstrual phase, also known as menstruation, begins on the first day of menstruation and lasts for five days. During this phase, the uterus sheds the inner lining of blood vessels and soft tissue which leaves ...... middle of paper ...... erone, estrogen and inhibin, to decrease so that the uterus can prepare to get rid of the tissue that was produced for the fertilized egg. (Wikipedia)A fertilized egg, the zygote, is produced when two gamete cells, male and female, fuse through sexual reproduction. After sexual reproduction, a single sperm can live between 48 and 72 hours. The sperm begin to swim towards the fallopian tubes to fertilize the egg waiting in the fallopian tube. Fertilization takes approximately 24 hours; Once the sperm enters the oocyte, it leaves the plasma behind and the egg changes surface so that another sperm cannot enter the egg. Once the sperm enters the egg, it completes its second meiotic division, which forms an egg and a second polar corpus. Within 24 to 48 hours after fertilization, the first signs of pregnancy can be detected. (Chronolab)