Menstrual Cycle Phases Explained
A woman has two ovaries. One on the left hand side of her lower abdomen and one on the right hand side.
The ovaries consist of follicles and inside the follicles are immature eggs. Do you know when a girl is born her ovaries already contains all the immature eggs that will later mature throughout her life time?
These eggs mature one at a time.
The job of the follicular stimulating hormones is to ripen an egg. While the egg is growing the follicle also stimulates an hormone called estrogen to help thicken the uterus lining in preparation for pregnancy.
The estrogen hormone level continues to rise and it reaches its peak at the middle of the cycle.
This then triggers the ovulation.
The Ovulatory Phase
Ovulation occurs when the matured egg is released from the ovary into the fallopian tube.
The rise to the peak of the estrogen hormone during the follicular phase causes the brain to produce an increasing level of the luteinising hormone.
An LH surge is what actually triggers ovulation. An this is why most ovulation tests detects ovulation by measuring the LH surge in a woman's urine.
Ovulation usually occurs at mid cycle between days 12- Day 16 depending on how long your cycle is.
The Luteal Phase
A new phase begins after ovulation until the end of the cycle. This is called the luteal phase. The left over of the follicle produces another hormone called progesterone. The released egg also stays in the fallopian tube for 24 hours waiting to be fertilised.
The progesterone hormone further thickens up the uterine lining picking up from where the estrogen hormone left off.
The purpose of the thickening is to prepare the womb for a fertilised egg so as to support a growing baby.
If no fertilisation occurs, the egg moves into the uterus and disintegrates
Also the level of the progesterone hormone starts to decrease because it is no longer needed to thicken the lining of the uterus.
Because of the decreased level of both the two most important sex hormone : estrogen and progesterone. The uterus lining is then shed when this two hormones are at their lowest.
This then causes mensuration and the beginning of another menstrual cycle.