There are four distinct phases in the menstrual cycle, they are:
- Follicular Phase
- Luteal Phase
Menstruation occurs when pregnancy has not occurred and the lining of the uterus breaks down and flows out through the vagina.
2. Follicular Phase
This is the phase from the first day of menstruation to ovulation. During this phase, Follicle Stimulating Hormone (FSH) is released causing between 10 and 20 follicles to start developing in the ovaries. Usually, only one of these follicles will mature to become an ovum (egg). As they develop, the follicles produce the hormone oestrogen, causing the lining of the uterus to become thick with blood vessels developed in preparation for possible implantation with a fertilized egg.
As oestrogen rises during the follicular phase, the production of another hormone – Lutienising Hormone (LH) is stimulated. The sudden rise in LH results in ovulation or the release of the ovum (egg) from the ovary. The egg is then swept by finger like extensions from the ovary into the fallopian tube and towards the uterus. If fertilisation does not occur, the ovum will deteriorate within 12 -24 hours.
4. Luteal Phase
The egg that was released from the ovary leaves behind a capsule called the corpus luteum. The corpus luteum secretes the hormone Progesterone in large amounts and also produces some oestrogen. The progesterone causes the endometrium to thicken and become well vasculated in preparation for fertilisation. Of course, if fertilisation does not occur, the lining is shed and the woman menstruates approximately 2 weeks from the time of ovulation.