The female menstrual, or uterine cycle, is a beautiful and natural part of life. When a girl is usually between the ages of 11-14, they will reach menarche. This is the initial onset of the menstruation cycle, which will come every single month for up to several decades except during pregnancy and if the patient is on certain types of birth control. Sometimes females will go through menarche very early, and some females will not get their period until later in life depending on genetic and lifestyle factors.
Each month, the body goes through the ovarian cycle, where the ovaries produce an ova, or egg, and that egg is either fertilized by a male sperm, or it dies and is released during the menstruation process. The ovarian cycle is a three stage process including the first ten days called the follicular phase, days 11-14 called the ovulatory phase, and the final days of the 28-day cycle referred to as the luteal phase. During the follicular phase, a follicle grows, which is an egg sac in the ovary. During this phase the follicle is preparing to release a mature egg for fertilization.
What follows is the ovulatory phase, which is the final preparation and releasing of the egg. This stage involves the corpus luteum, which is the same follicle from the follicular phase after it has released its ovum and begins to produce progesterone, one of the two key hormones for female sexual development and reproduction that is produced in the ovaries. During this stage, the corpus luteum will apply different levels of intensity, depending on if fertilization occurs or not, of secreting that hormone to keep a thick endometrial lining for implantation.
The menstrual cycle can last up to a week, but some women experience heavy periods lasting up to two weeks at a time. When the egg is not fertilized, the cervix muscles contract and shed the walls of lining that it has built up. This lining is made of tissues and blood vessels to help aid in fetal implantation and development so when the egg is not fertilized, this lining is not necessary. The cervix will then dilate and the menstrual fluid will flow down the cervix and out the vagina. This fluid is a combination of endometrial tissue, blood, and mucus.
First is the proliferative phase, where the lining in the uterus will rebuild. The body wants to prepare for pregnancy, so the endometrium will build up blood and tissue in the uterus. This is produced by estrogen, and takes about 9 days. After this is ovulation. Finally is the secretory phase, which can last up to two weeks, and stops at the start of the period. The pituitary gland will secrete LH, or luteinizing hormone which in turn leads to the ruptured ovarian corpus luteum to secrete progesterone, mixing with the estrogen, thickening the walls of the endometrium with blood vessels. If the egg is not fertilized, LH and progesterone levels drop, the corpus luteum is degenerated, and the menstruation phase begins again.