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Chapter: Obstetrics and Gynecology: Reproductive Cycles

Clinical Manifestations of Hormonal Changes

Hormonal changes induced by the hypothalamic-pituitary-ovarian axis and the adrenal gland trigger puberty, and hormones continue to exert a cyclic influence until a woman reaches menopause.



Hormonal changes induced by the hypothalamic-pituitary-ovarian axis and the adrenal gland trigger puberty, and hormones continue to exert a cyclic influence until a woman reaches menopause. At that time, the lack of cyclic ovarian function results in the permanent cessation of menstruation.


Various female structures undergo changes in response to the reproductive cycle hormones: the endometrium and endocervix, breasts, vagina, and the hypothalamus. Changes in the endo-cervix and breasts can be directly observed. Daily assess-ment of basal body temperature can identify changes in the hypothalamic thermoregulation center. Other changes can be assessed by cytologic examination of a sample from the vaginal epithelium or histologic evaluation of an endome-trial biopsy. A careful history may identify symptoms asso-ciated with hormone effects, such as abdominal bloating, fluid retention, mood and appetite changes, and uterine cramps at the onset of menstruation.



Within the uterus, the endometrium undergoes dramatic histologic changes during the reproductive cycle. During menstruation, the entire endometrium is expelled and only the basal layer remains. During the follicular phase, the rise in estrogen levels stimulates endometrial cell growth: the endometrial stroma thickens and the endometrial glands become elongated to form the proliferative endometrium. In an ovulatory cycle, the endometrium reaches maximal thickness at the time of ovulation.


When ovulation occurs, the predominant hormone shifts from estrogen to progesterone and distinct changes occur within the endometrium at almost daily intervals. Progesterone causes differentiation of the endometrial components and converts the proliferative endometrium into a secretory endometrium. The endometrial stroma becomes loose and edematous, while blood vessels enter-ing the endometrium become thickened and twisted. The endometrial glands, which were straight and tubular dur-ing the proliferative phase, become tortuous and contain secretory material within the lumen. With the withdrawal of progesterone at the end of the luteal phase, the endo-metrium breaks down and is sloughed during menses.


If ovulation does not occur and estrogen continues to be produced, the endometrial stroma continues to thicken and the endometrial glands continue to elongate. Only an endometrial biopsy will identify proliferative endometrium. The endometrium eventually outgrows its blood supply and sections of the endometrium slough intermittently. Without progesterone withdrawal to initiate desquamation of the entire endometrium, bleeding is acyclic and occurs outside of hormonal control irregularly and for prolonged periods of time. When women present with abnormal uterine bleeding, anovulatory bleeding is a common diagnosis. 



The endocervix contains glands that secrete mucus in response to hormonal stimulation. Under the influence of estrogens, the endocervical glands secrete large quantities of thin, clear, watery mucus. Endocervical mucus produc-tion is maximal at the time of ovulation. This mucus facili-tates sperm capture, storage, and transport. With ovulation, progesterone reverses the effect of estrogen on the endo-cervical mucus, and mucus production diminishes.

Some women monitor their cervical mucus to optimize the timing of intercourse when trying to conceive or in order to avoid conception. However, the timing of these changes is nonspecific and is an unreliable method of contraception




Estrogen exposure is necessary for pubertal breast devel-opment; however, reproductive cycle changes in the breast occur primarily due to progesterone effect. The ductal elements of the breast, nipple, and areola respond to progesterone secretion. Some women will notice more breast tenderness and fullness in the luteal phase due to progesterone-mediated changes.



Estrogen promotes growth of the vaginal epithelium and maturation of the superficial epithelial cells of the mucosa. During sexual stimulation, the presence of estrogen aids vaginal transudation and lubrication, which facilitates inter-course. During the luteal phase of the reproductive cycle, the vaginal epithelium retains its thickness, but the secre-tions are markedly diminished.

Hypothalamic Thermoregulation Center


Progesterone is a hormone with thermogenic effects; under the influence of progesterone, the hypothalamus shifts the basal body temperature upward by 0.5°F to 1.0°F over the average preovulatory temperature. This shift occurs abruptly with the beginning of progesterone secretion and quickly returns to baseline with the decline in progesterone secretion. Therefore, these changes in basal body temper-ature reflect changes in plasma progesterone concentration.

Since the basal body temperature assumes basal conditions at rest, it should be performed immediately in the morning upon awakening, prior to any activity.


Special thermometers with an expanded scale are available for this purpose. Identification of this characteristic bipha-sic curve provides retrospective, indirect evidence of ovula-tion; however, some ovulatory women do not demonstrate these changes (see Fig. 33.2)


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