Pocket ObGyn – Hormonal Regulation
See Abbreviations
The Menstrual Cycle
- Mean age of menarche: 4 y. Mean age of menopause: 51 y.
- 1st day of vaginal bleeding = day 1 of cycle; mean duration of bleeding is 4 ± 2 d; avg bld loss of 35 Mean cycle length 21–34 d (Clin Obstet Gynaecol 2010;2:157)
- Follicular phase: Lasts 10–14 d, variable in duration, determines menstrual cycle length
- Ovulation: Estrogen reaches very high levels (around day 14) ® LH surge ® dominant follicle rupture/oocyte Follicle remnant ® corpus luteum which secretes progesterone & maintains the endometrial lining (Am J Hum Biol 2001;4:465). If fertilization occurs, the trophoblast cells synthesize hCG to maintain the corpus luteum.
- Luteal phase: Lasts 12–15 d, constant in In the absence of Preg, the corpus luteum regresses ® progesterone levels drop ® uterine lining is shed & marks the beginning of the next period.
Figure 17.1 Menstrual cycle and hormones
(From Medical-Surgical Nursing Made Incredibly Easy! 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2007)
Hormones of Pregnancy
- hCG is secreted by placental Detected in the mother’s bld 8 d after conception. Maintains corpus luteum progesterone production. Structurally similar to LH, FSH, & TSH (same alpha-subunit). Doubles q48h early Preg. Max 8–10 w,
~100000 mIU/mL ® decline at 10–12 w ® nadir at 20 w.
- hPL is produced by Detected at 2–3 w after fertilization. Levels rise steadily until 34–36 w to a peak 5–10 mg/mL. Effects include mat lipolysis ® circulating free fatty acids to provide a source of energy for mother & fetus; anti-insulin action ® increased mat insulin levels ® increased prot synthesis; angiogenic action ® fetal vasculature formation
- Progesterone is mainly produced by the ovary until 6–7 w gest when the placenta begins to Maintains endometrial lining in early Preg & uterine quiescence. Production ~250–600 mg/d (prepregnancy 0.1–40 mg/d).
- Relaxin is secreted by the corpus luteum ® uterine relaxation, systemic vasodilation, & cardiac Serum concentrations peak at 1 ng/mL at 12–13 w ® fall to 0.5 ng/mL for the remainder of the Preg (Am J Physiol Regul Integr Comp Physiol 2011:R267).