Estrogen & progesterone

Overview of Female Sex Hormones

  • Estrogen and progesterone are the primary female sex hormones.

  • Produced mainly by the ovaries, which are the female gonads.

Types of Estrogens

  • Estradiol: Most biologically active; responsible for sex-specific changes during puberty, such as monthly ovulation and the development of secondary sex characteristics.

  • Estrone and Estriol: Other types of estrogens synthesized in smaller amounts.

  • Ovaries are the main source of estrogen and progesterone during the reproductive years; adrenal cortex and adipose tissue contribute small amounts.

Hormonal Regulation Before and During Puberty

  • Before puberty, the hypothalamus secretes gonadotropin-releasing hormone (GnRH) in small amounts.

  • GnRH stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

  • With the onset of puberty, GnRH is secreted in pulses, resulting in increased FSH and LH levels.

Ovarian Follicles

  • Ovarian follicles develop under FSH and LH influence.

  • Each follicle consists of follicular cells and a primary oocyte.

  • Follicular cells differentiate into theca and granulosa cells, essential for synthesizing estrogen and progesterone.

The Menstrual Cycle

  • Duration: Average of 28 days.

  • Phases:

    • Follicular Phase (2 weeks before ovulation): Primarily estrogen production, leading to the thickening of the endometrium and the expression of progesterone receptors.

    • Luteal Phase (2 weeks post-ovulation): Dominated by progesterone, aiding in preparing the uterus for potential pregnancy.

Feedback Mechanisms

  • Follicular Phase Feedback: Elevated estrogen levels provide negative feedback on FSH secretion.

  • Ovulation Trigger: A surge in estrogen just before ovulation converts to positive feedback, causing a spike in FSH and LH, leading to ovulation.

  • Luteal Phase Feedback: Progesterone provides negative feedback to reduce LH levels, resulting in decreased progesterone and the onset of menstruation.

Hormone Synthesis

  • Both estrogen and progesterone begin with cholesterol.

  • Cholesterol Desmolase: Converts cholesterol into pregnenolone; further processed into progesterone or other steroids (e.g., DHEA).

  • Granulosa Cells Activity:

    • Convert androstenedione (a testosterone precursor) into estradiol.

    • Controlled by FSH, leading to high estradiol availability during the follicular phase.

Local and Systemic Effects

  • Local Effects: Hormones act on nearby organs/tissues, facilitating reproductive organ maturation and changes in menstrual cycle physiology.

  • Systemic Effects:

    • Estrogen: Maintains blood vessel flexibility, sustains bone density, and lowers LDL cholesterol, protecting against cardiovascular disease.

    • Progesterone: Supports bone strength and skin elasticity.

Hormonal Changes During Pregnancy

  • The placenta secretes estrogen and progesterone, with estriol becoming the dominant estrogen.

  • Estriol and progesterone prepare breasts for lactation post-delivery.

Menopause

  • Typically occurs around age 50 due to depletion of functional ovarian follicles, leading to a significant drop in estradiol levels.

  • Symptoms include hot flashes and night sweats.

  • Post-menopause, adrenal glands and fat tissue produce small amounts of estrone, becoming the predominant estrogen type.

Conclusion

  • Estrogen and progesterone are vital throughout key life stages, namely puberty, the reproductive period, pregnancy, and menopause, significantly impacting female health.