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THE MENSTRUATION CYCLE (Anatomy and physiology (Menstruation is the cyclic…
THE MENSTRUATION CYCLE
Anatomy and physiology
Menstruation is the cyclic or periodic shedding of the endometrium of the uterus as characterised by monthly vaginal bleeding, which commences at puberty.
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In a normal menstrual cycle, there is an orderly cyclic production of hormones by the ovaries to stimulate ovulation and parallel proliferation of the endometrium of the uterus, in preparation for the implantation of the fertilised ovum,the embryo.
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Ovarian cycle
Follicular phase
During this phase, the mature ovum under the influence of the FSH enlarges to form a cyst-like structure known as the graafian follicle.
At this stage, the ovary also secretes oestrogen.
The graafian follicle migrates from the centre of the ovary to the surface where it bursts, releasing the ovum into the peritoneal cavity.
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The ovum, now called an oocyte, finds its way into the fallopian tube where it is carried to the uterus.
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Luteal phase
During this phase, the burst grafian follicles starts to heal and forms a yellowish scar on the ovary known as corpus luteum which secretes progesterone
Progesterone is necessary to promote proliferation of the endometrial cells for the endometrium to thicken and increase its vascularity in preparation of the ferlised ovum
Uterine cycle
The uterine cycle is divided into the proliferative and secretory phases and corresponds to the phases of the ovarian cycle.
During the follicular phase of the ovarian cycle, the increase of FSH and the secretion of oestrogen result in the proliferation of the endometrium, which becomes thick with increased blood supply in readiness for the reception of the embryo, should the oocyte be fertilised.
The secretory phase is marked by the endometrium reaching its peak in thickening and vascularisation, usually in the middle of the cycle.
The secretory phase is also maintained by the production of the LH, and the progesterone by the corpus luteum.
Should fertilization fail to occur, the FSH, LH, oestrogen and progen levels decrease, the unfertilised ovum disingrates and the endometrial layer becomes haemorrhagic and is shed in the process called menstruation
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