Systemic influence and the "menstrual wave" phenomenon
The action of sex steroids is not limited to the pelvic organs. In the days preceding menstruation, women exhibit the phenomenon of the "menstrual wave".
This is based on an imbalance between inhibitory and activating processes in the cerebral cortex, as well as fluctuations in the tone of the parasympathetic and sympathetic divisions of the autonomic nervous system. This has a noticeable effect on the cardiovascular system and clinically manifests as irritability and mood swings. In healthy patients, these changes do not exceed the physiological norm.
Role of the thyroid gland and adrenal glands
Extragenital endocrine glands take an active part in supporting reproductive function.
The thyroid gland (hormones T₃ and T₄) acts as a key regulator of metabolism. Its effect on the reproductive system is mediated through the liver: thyroid hormones stimulate the production of sex hormone-binding globulin. This makes it possible to control the balance between the active (free) and bound fractions of androgens and estrogens.
- In hypothyroidism (deficiency of T₃ and T₄), thyrotropin-releasing hormone secretion increases compensatorily. It activates pituitary lactotrophs, causing hyperprolactinemia. Simultaneously, the production of FSH and LH drops, which inhibits steroidogenesis and follicular growth.
- In hyperthyroidism, excess hormones sharply increase the level of binding globulin. The free estrogen fraction drops, resulting in hypoestrogenemia, which disrupts oocyte maturation.
The adrenal glands synthesize androgens (testosterone, androstenedione) in amounts equal to those of the ovaries. Specific adrenal hormones are DHEA and DHEA-S. The latter is secreted in maximum amounts, exhibits weak androgenic activity, and serves as a reserve form. The physiological purpose of producing these hormones is to provide a substrate for extragonadal estrogen synthesis.
Effects of progesterone: basal temperature
Basal temperature assessment is a basic functional diagnostics test based on the thermogenic property of progesterone. In the second (luteal) phase of the cycle, increased progesterone levels act on the hypothalamic thermoregulation center, causing transient hyperthermia.
Measurements are taken rectally every morning before getting out of bed.
- Follicular phase: temperature remains at 36.1–36.6 °C (does not exceed 37 °C). A brief dip on the chart is possible before ovulation.
- Luteal phase: there is a rise of 0.4–0.8 °C (above 37.0 °C), which persists until the end of the cycle.
- Before menstruation: the corpus luteum regresses, progesterone drops, and temperature returns to baseline values.
A persistent biphasic chart confirms ovulation. The absence of a rise indicates anovulation. If the rise is delayed, lasts less than 2–7 days, or does not exceed 0.2–0.3 °C, corpus luteum insufficiency is diagnosed. False-positive results are possible in case of infections or increased CNS excitability.
Effects of estrogens: cervical symptoms
A group of tests reflecting the body's estrogen saturation is based on changes in the properties of cervical mucus. Genital inflammation and hormonal imbalance reduce the diagnostic value of these methods.
- «Pupil» sign. Reflects gaping of the external os of the uterine cervix due to the accumulation of clear mucus. In the first phase, mucus synthesis increases. By the time of ovulation, the os is maximally dilated (rated as `+++`). In the second phase, under the influence of progesterone, the os closes, the sign fades (`+`) and disappears.
- Crystallization sign («fern» phenomenon). Air-dried cervical mucus forms crystals. The severity increases during the follicular phase, peaks at ovulation (graded as 1–3 points or up to `++++`), and completely disappears before menstruation.
- Cervical mucus spinnbarkeit (stretchability). The mucus is extracted with sponge forceps and the blades are separated. During the peak estrogen concentration (ovulation), the length of the thread before rupture reaches 10–12 cm.
Cytological picture: karyopyknotic index
Estrogens stimulate the proliferation of the basal layer of the stratified squamous epithelium of the vagina. This leads to the accumulation of dying (keratinizing) cells in the superficial layer. The first stage of their death is accompanied by nuclear changes — karyopyknosis.
The karyopyknotic index (KPI) is the percentage of cells with a pyknotic nucleus relative to all epithelial cells in the smear.
- At the beginning of the follicular phase, the KPI is 20–40%.
- In the preovulatory days, against the background of maximum estrogen levels, the index surges to 80–88%.
- In the luteal phase, the indicator drops to 20–25%.
For quick memorization of tests: Estrogens mean Expansion (cervical opening, mucus stretchability, increased crystallization, and KPI). Progesterone means Progesterone-induced Pyrexia (increase in basal temperature) and Pause (disappearance of the pupil and fern signs).
Class and exam questions
Why does the basal temperature rise in the second phase of the cycle?
This is the result of the thermogenic action of progesterone. It directly affects the thermoregulation center in the hypothalamus, causing transient hyperthermia (an increase of 0.4–0.8 °C).
How does hypothyroidism affect reproductive function?
Thyroid hormone deficiency causes a compensatory release of thyrotropin-releasing hormone. This leads to hyperprolactinemia and inhibition of LH and FSH secretion, which blocks follicular maturation in the ovaries.
What does the karyopyknotic index (KPI) show?
The KPI reflects the percentage of keratinizing cells in the vaginal smear. It is an accurate marker of the body's estrogen saturation: at the peak of ovulation, it reaches 80–88%.
What else to study on this topic
- Levels of regulation of the normal menstrual cycle
- Principles of positive and negative feedback in the endocrine system
- Cyclic changes in the endometrium of the uterus
- Instrumental diagnostics: dynamic ultrasound in IVF programs
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