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Pathophysiology of the Menstrual Cycle
Cyclic changes in hormone levels affect the uterus, cervix, and vagina. The following summary is adapted from Lichtman.
Uterus
The uterus increases in size in the late proliferative and early secretory phases. This is due to the increasing thickness of the endometrium. As estrogen levels rise, rhythmic contraction of the uterus increases. This is thought to aid the movement of sperm toward the oviduct. The contraction
abates with progesterone, which may assist implantation. Click here for more about hormone effects on the uterus.
Vagina
Estrogen stimulation in the first part of the menstrual cycle causes changes in vaginal cells and cervical mucus. The mucus thins in response to estrogen and becomes much different from the thick, sticky secretions after menstruation. The clearer watery secretions, associated with rising estrogen levels, can form a fern pattern when spread onto a glass slide to dry. The fern
pattern is associated with peak estrogen levels before ovulation, perhaps facilitating sperm motility.
Cervix
The cervical os widens under the influence of estrogen. At ovulation it may be partially open, and it closes again during the luteal phase.
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Physiologic changes associated with the menstrual cycle. The bers
0 to 4 indicate an increasing characteristic of cervical mucus.
From Seidel.
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