Two hormones, two jobs
The ovary makes two main hormones, and the easiest way to remember them is by what they do. Estrogen is the builder: it thickens the lining of the uterus, drives the changes of female puberty, and keeps bone and blood vessels healthy. Progesterone is the holder: once estrogen has built the lining, progesterone makes it stable, quiet, and ready to support a pregnancy. Think of estrogen as the team that constructs a room and progesterone as the team that furnishes it and keeps it calm.
“Estrogen” is really a family. The most powerful member during the reproductive years is estradiol — when people say a woman's estrogen level, they usually mean estradiol. (Estriol matters mainly in pregnancy, and a weaker estrogen called estrone dominates after menopause.) Throughout this track, when we say estrogen we mostly mean estradiol.
They are steroids — made from cholesterol
Both estradiol and progesterone are steroid hormones, which tells you three useful things at once. First, they are built from cholesterol, step by step, so progesterone is actually an early precursor on the road that ends in estrogen. Second, because they are oily (lipophilic), they slip right through cell membranes instead of knocking on a surface door. Third, they act slowly and deeply: inside the cell they bind an intracellular receptor — a nuclear receptor — that switches genes on and off. That is why estrogen's effects, like thickening a lining, take days rather than seconds.
One enzyme deserves a name now because it returns again and again: aromatase. It is the final step that converts androgens (male-type steroids) into estrogen. Yes — estrogen is made *from* androgens. Hold onto that fact; in the next guide it explains why the ovary needs two different cell types working together.