Definitions
- Puberty (see Chapter 21) is a general term encompassing the entire transition from childhood to sexual maturity.
- Menarche (the onset of menstruation) occurs at an average age of 12 years (normal range 8–16 years).
- Menstrual cycles or “periods” are often irregular through adolescence before settling into a more consistent ovulatory pattern ranging from 24 days to 35 days (average 28 days). The average duration of menstruation is 3–7 days and blood loss is typically about 80 mL.
- Mittelschmerz refers to periovulatory, unilateral, pelvic pain that some women consistently experience.
- Menopause (see Chapter 28) is defined as the cessation of menses and usually occurs around age 50. Women with continued bleeding beyond age 55 should be sampled to rule out malignancy.
Hormonal regulation of ovulation (Figure 3.1)
The cyclopentenophenanthrene ring structure is the basic carbon skeleton for all steroid hormones. Cholesterol is the parent steroid from which all the glucocorticoids, mineralocorticoids, and gonadal steroids are derived.
Phases of the menstrual cycle
- The menstrual phase begins on day 1 with the onset of bleeding and continues for several more days until the shedding of the endometrial lining stops (usually day 4–5).
- The proliferative phase begins at the end of the menstrual phase and ends at ovulation (usually day 13 or 14). This phase is characterized by endometrial thickening and ovarian follicular maturation.
- The luteal (secretory) phase starts at ovulation and lasts through day 28 before the entire process starts over again on day 1.
Biologic basis of menstruation (Figure 3.2)
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