Hormones 101: educational physiology

This is educational physiology — not a discussion of therapy. Any treatment decisions belong with a provider.

Estrogen (estradiol is the main form) is produced primarily by the ovaries in the reproductive years. It regulates the menstrual cycle and has receptors throughout the body — brain, bone, skin, blood vessels, urinary tract. Its decline in the transition explains why so many organ systems are affected.

Progesterone is produced after ovulation and prepares the uterine lining. In perimenopause, ovulation becomes less consistent, so progesterone patterns become erratic. Progesterone also produces a calming metabolite (allopregnanolone) that acts on GABA receptors — one biological reason anxiety often rises when its production drops.

FSH (from the pituitary) signals the ovaries to grow follicles. As ovaries respond less consistently, FSH rises. A single FSH measurement isn't a reliable diagnostic in perimenopause because levels swing widely.

LH triggers ovulation. AMH reflects the ovarian follicle pool and helps estimate proximity to menopause without predicting it precisely.

Testosterone is present in women too — produced by ovaries and adrenals in small amounts. It gradually declines with age and is associated with libido, energy, and muscle mass.

The HPO (hypothalamic-pituitary-ovarian) axis is the feedback loop coordinating all of this. Perimenopause is essentially the gradual desynchronization of that loop.