The onset of menstruation is called menarche. There are a variety of intervals between periods. That 28-day cycle you have heard about is really a myth because few woman have a perfectly regular cycle. The interval between periods may change many times during a woman’s life-time. There are many circumstances that may affect the menstrual cycle, such as: illness, abrupt change of climate, or severe emotional stress. The menstrual cycle is particularly irregular just after puberty and again at menopause.
Some women may experience premenstrual tension, exhibiting symptoms such as: headache, bloating of the abdomen, fullness and pain of the breasts, increased irritability, depression, and emotional instability. These symptoms may occur 10-14 days prior to the onset of the menstrual period and usually disappear hours after the menstrual flow starts.
The pituitary gland, also called the master gland, produces and stimulate the growth hormones. It is through the blood that this information is carried to the bones and tissue. This gland is about the size of a pea at menarche and is located at the base of the brain. It is the pituitary gland that notifies the gonads that it is time to start functioning. The pituitary sends a follicle-stimulating hormone to stimulate the growth and development of follicles in the ovaries. The ovaries secrete estrogen which aid in the maturation of the follicle.
The ovaries are two glands containing thousands of follicles or egg sacs on either side of the uterus. Once a month ovulation occurs. In one of the 2 ovaries an egg or ovum matures and breaks out of its sac or graafian follicle and out of the ovaries. Luteotropic hormone (LTH) secrete progesterone which aid in follicle growth and maturation.
The two fallopian tubes, with fringed open ends near the ovaries, are less than 5 inches long. These tubes provide passageway to the uterus. It is also through these tubes that the egg travels to the uterus after ovulation. The uterus or womb is a hollow organ. The lining is called the endometrium, from which the menstrual flow comes. Every month the lining of the uterus (endometrium) builds up into a spongy mass of tissue containing blood to form a bed for the fertilized egg. If the egg is unfertilized itwill disintegrate and will shed.
The menstrual cycle is divided into four phases:
1. the menstrual phase – the actual shedding of the endometrium
2. post menstrual phase – this is resting stage immediately following menstruation. During this time, the pituitary sends out hormones to the ovum and another egg begins to ripen
3. intermenstrual phase the ovaries releases a hormone which stimulates the endometrium and causes it to thicken. Ovulation occurs (a mature egg breaks out of the graafian follicle) the mature egg enters the fallopian tube, and the endometrium provides a nesting place for its development
4. premenstrual phase – the lining of the uterus continues to grow and thicken in preparation for the fertilized egg. If the egg is not fertilized the corpus luteum stops producing progesterone and the egg disintegrates.The lining is shedded and a new cycle commences. If fertilization and implantation does take place the corpus luteum continues secreting progesterone and menstruation does not occur.
The proliferative phase includes the postmenstrual phase and the intermenstrual phase. It is during this phase that the hormone estrogen that is produced by the ovaries prepares the uterus and the walls begin to thicken.
The secretory phase which is the premenstrual phase. It is during this phase that ovulation occurs and the portion that remains in the ovary is called the corpus luteum. The corpusluteum secretes progesterone that prepares the lining of the uterus to receive and nurture the fertilized egg.
During the normal menstrual flow, the individual discards 1-1/2 to 5 ounces of blood over the several days. This loss of blood is quickly replaced and does not cause weakening.