Conversation so far:
what is the function of the endocrine system
The endocrine system is made up of glands that produce and secrete hormones, chemical substances produced in the body that regulate the activity of cells or organs.
what glands are there in the endocrine system
The major glands of the endocrine system are the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal body, and the reproductive organs.
which reproductive organs are in the endocrine system
The reproductive organs in the endocrine system are the ovaries and testes.
what are the main hormones produced by the reproductive organs
The main reproductive hormones are estrogen and testosterone.

Question: what produces estrogen
Self-contained rewrite: what organ produces estrogen