MENSTRUAL CYCLE

What is Menstruation?


Shortly after the beginning of puberty in girls, and usually about 2 years after the development of breasts, menstruation starts. While menstruation usually begins between ages 12 and 13, it may happen at a younger or older age. The first menstrual period is called "menarche."

Menstruation is the periodic discharging of the menses, the flow of blood and cells from the lining of the uterus in females. 

The menstrual cycle is about four weeks long, starting on the first day of bleeding and ending when the next period begins. However, it can vary greatly when a girl first starts her period. It may skip months or come several times per month in the beginning. 

What is a menstrual cycle?

The menstrual cycle is the series of changes a woman's body goes through to prepare for a pregnancy. About once a month, the uterus grows a new lining (endometrium) to get ready for a fertilized egg. When there is no fertilized egg to start a pregnancy, the uterus sheds its lining. This is the monthly menstrual bleeding (also called menstrual period) that women have from their early teen years until menopause, around age 50.

The menstrual cycle is from Day 1 of bleeding to Day 1 of the next time of bleeding. Although the average cycle is 28 days, it is normal to have a cycle that is shorter or longer.

Girls usually start having menstrual periods between the ages of 11 and 14. Women usually start to have fewer periods between ages 39 and 51. Women in their 40s and teens may have cycles that are longer or change a lot. 

 

What controls the menstrual cycle?

Hormones control the menstrual cycle. During each cycle, the brain's hypothalamus and pituitary gland send hormone signals back and forth with the ovaries. These signals get the ovaries and uterus ready for a pregnancy.

The hormones estrogen and progesterone play the biggest roles in how the uterus changes during each cycle.

• Estrogen builds up the lining of the uterus.
• Progesterone increases after an ovary releases an egg (ovulation) at the middle of the cycle. This helps the estrogen keep the lining thick and ready for a fertilized egg.
• A drop in progesterone (along with estrogen) causes the lining to break down. This is when your period starts.

A change in hormone levels can affect the cycle or fertility. For example, teens tend to have low or changing progesterone levels. This is also true for women close to menopause. That is why teens and women in their 40s may have heavy menstrual bleeding and cycles that change in length.

Other things can change menstrual cycle. They include birth control pills, low body fat, losing a lot of weight, or being overweight. Stress or very hard exercise also can change your cycle. Pregnancy is the most common cause of a missed period.

 

The Phases of the Menstrual Cycle

1. Follicular Phase
2. Ovulation Phase
3. Luteal Phase
4. Menstruation Phase

THE FOLLICULAR PHASE

Also called proliferative phase or pre-ovulatory phase.

In this phase, the hypothalamus in the brain signals the anterior pituitary gland to start secreting the hormones FSH (Follicle-Stimulating Hormone) and LH (Leutanizing Hormone) to the ovaries. It is this FSH that will stimulate the maturation and release of a follicle from the ovary. The follicle, before it matures, would then secrete the hormone estrogen, which acts as a repairman in the uterine wall (or endometrium) to allow its walls to proliferate and start to thicken.

As the cells in the walls of our uterus start proliferating, we would have an increased thickness in our uterine linings. This thickening of the wall is a natural phenomenon to prepare our body for the possible implantation of the egg in the uterus where the fetus would grow for about 40 weeks. If, however, the egg does not get fertilized, the uterine linings would start to shed and this would give us the red bloody discharge.

THE OVULATION PHASE

After the thickening of the uterine wall and the maturation of the follicle in the proliferative phase, we would then reach the ovulation phase. From the word alone, we probably have deduced that it is the time period when we are most fertile.

In this phase, the mature follicle ruptures open and the ripe egg is released.The hair-like projections in the fallopian tube starts to sweep the the egg to go to one direction. It is the hormone LH that will stimulate the opening of the follicle, release the ovum and other follicular fluids containing estrogen.

THE LUTEAL PHASE

The raptured follicle in the last phase would become a corpus luteum, which would continue secreting estrogen. However, as the levels of LH surge, the levels of estrogen lowers.

This would also increase the level of the hormone progesterone, which is responsible for the receptiveness of the uterine linings for the coming ovum. Other effects of this hormone are breast sensitivity and engorgement, the degeneration of the corpus luteum to corpus albicans and the decrease of this hormone would trigger menstrual flow.

The two functions of the corpus luteum are:

1. To provide hormonal stimulus to the organs that are targeted
2. To regulate the menstrual cycle

If the ovum is not fertilized, the corpus luteum will continue to secrete the hormones progesterone and estrogen for 14 days, before it turns to corpus albicans. This corpus albicans do not get released out of the body with the onset of menstruation. It just stays there and build up.

However, if the ovum is fertilized, the embryo will implant itself in the uterine wall and start secreting the hormone hCG (Human Chorionic Gonadotropin), which would signal the corpus luteum to continue secreting progesterone and estrogen and not turn into corpus albicans. At this stage, the corpus luteum is now called a fancier term-- corpus luteum graviditatis, until the placenta is fully made and capable of producing progesterone.

THE MENSTRUAL PHASE

This is the phase when the uterine lining get sloughed off or get shed in a menstrual flow.

The corpus luteum deteriorate into a corpus albicans if the ovum is not fertilized. There would be a decrease of the hormone progesterone and this would cause some blood vessels in the uterus to contract, which means that the blood supply is significantly lowered. The ischaemic endometrium would then be shed and for about one week, we would have menstruation.