Menstrual cycle: proliferative or follicular phase
MENSTRUAL CYCLE: PROLIFERATIVE OR FOLLICULAR PHASE
The menstrual cycle involves a series of hormonal events which occur at fairly regular intervals. The average menstrual cycle is approximately 28 days, although this may vary considerably between women. The menstrual cycle involves four distinct phases:
Day 1-5: menstruation (the menstrual period);
Day 3-13: the proliferative or follicular phase;
Day 14: ovulation;
Day 15-28: the luteal or secretory phase.
Although the first day of menstruation is usually referred to as the start of the menstrual cycle, the menstrual period (days 1-5) is actually the culmination of the hormonal changes which make up the menstrual cycle. Therefore, in our explanation of the menstrual cycle we will start by looking at the proliferative phase (days 3-13) and we will use a 28-day cycle to explain the process.
Proliferative or follicular phase-The proliferative phase extends from the time of menstruation to ovulation. It is known as the proliferative phase because it is the phase during which the endometrium begins to thicken or proliferate in readiness for implantation of the fertilised ovum. It is sometimes also known as the follicular phase.
During the proliferative phase the pituitary gland releases the follicle stimulating hormone (FSH) which stimulates the growth and development of several ovarian follicles in the ovary. These follicles enlarge and move towards die surface of the ovary. However, usually only one follicle continues to grow and undergo the full cycle of growth and development.
During the proliferative phase the oestrogen levels in the bloodstream rise progressively until just prior to ovulation. The rising oestrogen levels stimulate the endometrium to proliferate so that it is ready to nourish a fertilised ovum.
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