corpus luteumThe female reproductive system is entirely internal.The vagina is the canal that leads from the outside of the body to the cervix, the opening to the uterus.

The uterus is the muscular organ where a fertilized egg or embryo attaches & develops. It is the size & shape of a pear & lined with a rich & nourishing membrane, the endometrium The fallopian tubes extend from the top of the down over the ovaries, the two walnut-sized organs that contain the eggs.
The eggs in each ovary are made before a woman is born. The most eggs a woman will ever have – about 7 million is when there’s still 20 weeks to go before birth. From this time on, the numbers eggs will be replaced. A girl is born with about 2 million eggs. At the time, she has her first period there are about 400,000.
Every month from puberty to menopause, eggs begin to mature inside several fluid-filled ‘cysts’ within the ovaries, called follicles. Only one of these follicles will become dominant, while the others will shrink & be absorbed by the ovary. At mid-cycle, the dominant follicle releases a single egg during ovulation, when then travels down the fallopian tube toward the uterus.
For a pregnancy to occur, fertilization happens in the fallopian tube, when the egg meets sperm. The developing embryo then travels down the fallopian tube to the uterus, where it will implant in the endometrium approximately 7 days after ovulation.
Hormones control the highly complicated sequence of events leading to ovulation. The pituitary gland in the brain produces the two hormones that the ovary needs.
>> Follicle stimulating hormone ( FSH)
>> Luteinising hormones ( LH)

As these hormones are released, the monthly menstrual cycle occurs in three phases:

PHASES OF THE MENSTRUAL CYCLE

Follicular Phase: :
This begins on day 1 of the menstrual cycle, the first day of menstrual bleeding. FSH begins by stimulating the development of many follicles, but as levels of FSH gradually fall in a natural cycle only one follicle will dominate & go on to produces a mature egg. The non-dominant follicles are absorbed by the ovary & cannot be used again. The developing follicle also secretes estrogen, which has several functions. For example, estrogen develops the watery mid-cycle changes in cervical mucus that assist the passage of sperm into the uterus & also causes the thickening of the endometrium required for implantation. The main estrogen the ovary produces is estradiol.
Ovulatory Phase: :
This phase is short. It begins when, in response to rising estrogen levels, the level of LH rises dramatically. This LH surge triggers final maturation of the egg.The rupture of the follicle & then the release of the eggs. This usually happens 14 days before the next period is due or on day 14 of a 28-day cycle.
Lutel Phase: :
Begins after ovulation, at this point, the ovarian follicle where the egg developed collapses & solidified to become the corpus luteum