Characterized by several physical and emotional changes that take place in the body over a period of time, the menstrual cycle in women is responsible for the process of fertilization and reproduction. The entire cycle is divided into three significant phases.
These include the follicular phase (also called the proliferative phase), the ovulation phase and the luteal phase. Here’s a detailed look at what happens during each of these phases.
Different Phases of the Menstrual Cycle
The Follicular Phase
During the first few days of the menstrual cycle, the levels of the Follicle Stimulating Hormone (FSH) would increase drastically in the body. This leads to the stimulation of the developed ovarian follicles which try to dominate each other.
With time, all except one ovarian follicle would stop growing and the now dominant follicle would continue to mature into the ovum. At this stage, the dominant follicle would be referredto as a Graafian follicle or a tertiary.
It is at this stage that the developing follicles start secreting high amounts of estrogen which stimulate the formation of a thin uterine wall or endometrium. The uterine lining is also called as the proliferative endometrium and that is why this particular stage is also called as the proliferative phase.
The Ovulation Phase
Starting on the 12 th day of the menstrual cycle and lasting for about 2 days, the ovulation phase is characterized by the increased production of the Luteinizing Hormone (LH) which is otherwise called the LH surge. Produced by the anterior pituitary gland, the excess levels of LH would in turn make the follicle walls in the ovary weak enough to slip out the fully mature egg (also called as oocyte).
It is not clear as to which ovary (left or right) would release the oocyte first. In some cases, if both ovaries release an oocyte each at the same interval, the chances of conceiving fraternal twins are high.
With time, the oocyte turns into an ootid and then a mature ovum which is about .2mm wide. The mature ovum then passes into the fallopian tube via the fimbria (a tissue) located at both ends of the tube. In the absence of fertilization, the ovum would most probably dissolve in the fallopian tube itself, which is quite normal for a regular menstrual cycle.
The ovulation phase is preceded by a pain called mittelschmerz (translating to ‘middle pain’) which is experienced by almost every other fertile woman. This pain can be attributed to the sharp change in the hormonal levels. At times, women can also experience mid cycle flow.
The Luteal Phase
Also called as the Secretory Phase, the Luteal Phase in the menstrual cycle is characterized by the increased production of a variety of hormones including progesterone by the solid body called corpus lutuem that is formed in the ovary after the egg passes into the fallopian tube.
The progesterone produced by the corpus lutuem in turn produces enough estrogen in addition to suppressing further production of the LH and FSH hormones. With the significant decrease in these two hormone levels in the body, the corpus lutuem withers, thus reducing the production of progesterone with it. And this final stage in the luteal phase triggers the final process of menstruation, i.e. shedding which will usually occur 14 days after the ovulation phase.