The functioning of female reproductive system revolves around the monthly cycle of hormonal activity, which results in a series of changes in the female reproductive organs, thus preparing her body for pregnancy.
Menstrual cycle begins in girls at puberty and continues until menopause. The entire cycle is governed by hormones FSH and LH, which are secreted by the pituitary gland located inside brain.
Menstrual cycle can be divided into 3 phases based on the activity in the ovary (ovarian cycle) and in the uterus (uterine cycle). The ovarian cycle can be divided into follicular phase, ovulation and luteal phase. Likewise, the uterine cycle can be divided into menstruation, proliferative phase and secretory phase.
Let's understand a bit more about the ovarian cycle.
1. Follicular phase: This phase is marked by beginning of menstruation at the beginning of a new menstrual cycle. Pituitary gland secrets Follicle Stimulating Hormone (FSH) to stimulate the ovaries, as a result of which, a number of eggs start growing in the ovaries. Each egg is contained in a bag of fluid and is called a follicle. At the end of this phase, a single dominant follicle is ready for ovulation to release the egg.
2. Ovulatory phase: Ovulation, the process of release of eggs, is triggered by release of Luteinising Hormone (LH) from the pituitary gland. The egg, thus released, is captured by the the fallopian tubes, which push it gently towards the uterine cavity.
3. Luteal phase: Shell of the follicle remaining after ovulation develops into "corpus luteum", which releases progesterone and oestrogen. Progesterone supports pregnancy by causing secretory changes in the uterine lining, which enable the fertilised egg to get implanted.
Egg gets fertilised by the sperm inside the fallopian tube, from where the fertilised egg travels to the uterus to get implanted, thereby resulting in pregnancy. Corpus luteum continues to release hormones to support pregnancy.
In case there is no pregnancy, the corpus luteum dissolves. As soon as the hormone secretion stops the uterine lining sheds off leading to menstruation and initiation of a new menstrual cycle.