(1) The menstrual (destructive) phase
The menstrual phase. The uterus lining (i.e., endometrium) and its blood vessels slough off , and is discharged with blood, mucus, cell debris and other fluid as the menses , through the vagina. This may last for 4-5 days. Menses occur when fertilization does not take place.
(2) The proliferative (follicular) phase
The proliferative phase occurs between the end of menses, and ovulation. In this phase, under the stimulation of estrogen, the uterine endometrium undergoes a process of growth (proliferation) and a new thick endometrium is formed. In the ovary, the follicle begins to develop into a Graafian follicle. This phase cycle days 6 to 13 or 14 in a 28 day cycle.
(3) The ovulatory phase
The ovulatory phase indicates the rupture of the Graafian follicle and release of the ovum (ovulation). It occurs some 14 days after the start of menstruation. During this phase the concentration of estrogen is high in blood and it stimulates the ovulation. The blood vessels enlarge and grow in the endometrial wall, and some secretory cells or glands are formed.
(4) The secretory (luteal) phase
The secretory phase occurs between ovulation and the onset of menses, i.e., the phase lasts about 14 days (cycle days 15 to 28). The endometrium which is under the influence of progesterone and estrogen, increases in size, becomes thick, the endometrial glands become enlarged, undergo maximum secretory activity and its blood vessels become coiled and enlarged
These hormones regulate the menstrual cycle.These hormones have profound effects on the ovaries and the uterus.
The anterior pituitary gland produces two gonadotrophic hormones: the follicle stimulating hormone (FSH) and the luteinizing hormone (LH). FSH stimulates the ovarian follicle to mature and secondly, it stimulates the follicle to produce estrogen. The estrogen brings about healing and repair of uterine wall (endometrium) following menstruation.
