An increase in the hormone estrogen causes secondary sex characteristics
Eggs in the ovaries begin to mature and are released during ovulation, usually at the rate of one per cycle, the menstruation occurs as a result of ovulation but only if no ovum is fertilized
The ovaries are the organs that produce eggs, which may fertilize by the sperm. The endometrium is the mucus membrane that lines the inside wall of the uterus. The lining is prepared each cycle to provide a kind of "nest of tissue" in which the fertilized – the new human life – will implant in order to develop. If the egg is not fertilized, the endometrium degenerates and is shed as a menstrual bleeding at the end of the cycle
The passageways by which eggs travel from the ovary to the uterus are the Fallopian tubes. The eggs grows in the ovary, surrounded by a group of cells called a follicle. At the start of each cycle, the brain tells the follicle to begin to mature. As the follicle matures, it sends a signal to the cervix to start producing the mucus. At the height of the process, the ripe egg bursts out of the follicle. This is ovulation
If there has been an act of intercourse between husband and the wife, fertilization of the egg by the sperm will take place in the outer part of the Fallopian tube. The time in which the egg can be fertilized is very short. If it does not meet with the sperm during this time, it degenerates within 24 hours