Female Sex Hormones and Their Physiological Functions

Estrogens Overview

• Estradiol is the principal estrogen in premenopausal women, playing a key role in reproductive health.
• After menopause, estrone becomes the primary circulating estrogen, replacing estradiol.

Types of Estrogens

• Estriol is significantly less potent than estradiol and is present in considerable amounts during pregnancy.
• Ethinyl estradiol is a synthetic estrogen that has a long duration of action and slow metabolism, making it effective for various therapeutic uses.

Physiological Functions

• Estrogen primarily promotes the proliferation of the endometrium, preparing it for potential implantation of a fertilized egg.
• The main physiological action of estrogens in target tissues involves binding to estrogen receptors, initiating transcription of estrogen-responsive genes.

Hormone Therapy and Administration

• Estrogen-progesterone therapy (EPT) is a common postmenopausal hormone therapy aimed at alleviating menopausal symptoms and preventing osteoporosis.
• Estrogens, both naturally occurring and synthetic analogs, are primarily administered through oral routes, patches, or other delivery systems.

Bioavailability and Additional Considerations

• The low bioavailability of orally administered estrogens is mainly due to first-pass metabolism in the liver, which significantly reduces the amount that enters systemic circulation.
• For women who have had a hysterectomy, estrogen-only therapy is recommended to mitigate menopausal symptoms without the need for additional progesterone.

Summary of Estrogen Functions

• Not all physiological functions of estrogen include ovulation induction; functions also encompass regulation of fat distribution, treatment of osteoporosis, and maintenance of reproductive tissues.