The Phases of Menstrual Cycle
WHAT IS THE MENSTRUAL CYCLE?
We constantly undergo changes in our body physiologically which is why it is important to learn about it. If we have a better understanding about its physiology (function) and what we actually go through every day, we can use it to our advantage and even make changes in our diet to suit us.
Usually, menstruation (or the shedding of the uterine lining) occurs every 28 days. This can vary from woman to woman, can fluctuate or can be quite irregular. So throughout that 28 days, our body is not just experiencing one, unchanging condition. Since the menstrual cycle is controlled by our hormones (endocrine system), we are actually experiencing a rise and fall of these hormones. This means that our bodies and our moods fluctuate as well. It is important to know the importance of maintaining balance (or homeostasis) so that we would not alter/affect the normal release of ovulating hormones in our body.
Read on and find out what we go through every 28 days. The illustration below summarizes the phases of menstrual cycle.
The four phases of the menstrual cycle are:
- Follicular Phase
- Ovulation Phase
- Luteal Phase
- 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:
- To provide hormonal stimulus to the organs that are targeted
- 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.
A fantastic video which explains the story of menstruation.