Female Reproductive Cycle
When a female child is born, she already has a complete supply of approximately 400,000 immature eggs. From puberty until menopause, these eggs are released from the ovaries one at a time.
The female reproductive system is entirely internal. The passage that connects the cervix and the uterus to the outside of the body is called the vagina. The uterus is a muscular organ approximately the size of a pear, it is lined with a mucous membrane called the endometrium. The fallopian tubes extend backward and downward from the top of the uterus. The fallopian tubes are connected to the ovaries which house follicles each containing an immature egg.
The Female Reproductive Cycle
A key element of reproduction is the woman's menstrual cycle. This cycle can be divided into three phases:
During this phase, a hormone known as FSH stimulates a follicle to secrete estrogen. Estrogen widens the cervix and changes the consistency of the cervical mucus to ensure better accessibility for sperm. During the follicular phase, one follicle will become dominant and the egg within it will begin to mature.
In the next phase, LH level increases dramatically and causes the ovary to release a ripened egg. In a typical 28 day cycle, this usually occurs 14 days after the first day of a woman's period.
During this final phase, the ovarian follicle that nurtured the egg prior to ovulation becomes known as the corpus luteum. The corpus luteum secretes a hormone known as progesterone that prepares the uterine lining to nourish a fertilized egg.
If fertilization does not occur during this cycle, the corpus luteum ceases to function around the 26th day and the uterine lining breaks down and sheds. The shedding of the uterine lining is known as a menstrual period.