Article

Hormonal Cycle

The hormonal cycle in women refers to the recurring, coordinated fluctuations of key reproductive hormones—primarily estrogen, progesterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH)—that regulate the menstrual and ovarian cycles. These cycles are essential for fertility, sexual function, and overall reproductive health.

Overview

The hormonal cycle is governed by the hypothalamic-pituitary-ovarian (HPO) axis:

Hypothalamus releases gonadotropin-releasing hormone (GnRH)
Pituitary gland releases FSH and LH in response
Ovaries produce estrogen and progesterone, which act on the uterus and other tissues

Phases of the Hormonal Cycle

1. Follicular Phase (Days 1–14)

Begins with menstruation (shedding of the uterine lining)
FSH stimulates growth of ovarian follicles
Dominant follicle produces increasing estrogen
Estrogen thickens the endometrial lining and provides negative feedback to FSH, but positive feedback to LH as ovulation approaches

2. Ovulation (Around Day 14)

Surge in LH (and FSH) triggers release of a mature egg from the ovary
Estrogen peaks just before ovulation

3. Luteal Phase (Days 15–28)

Corpus luteum forms from the ruptured follicle and secretes progesterone (and some estrogen)
Progesterone prepares the endometrium for possible implantation
If no pregnancy occurs, corpus luteum degenerates, progesterone and estrogen drop, and menstruation begins

Hormonal Interactions and Feedback

Negative feedback: Estrogen and progesterone inhibit GnRH, FSH, and LH to prevent overstimulation
Positive feedback: High estrogen levels mid-cycle trigger the LH surge (ovulation)

Key Hormones

Estrogen: Stimulates endometrial growth, secondary sex characteristics, and libido
Progesterone: Stabilizes endometrium, supports early pregnancy, modulates mood and sleep
FSH: Stimulates follicle growth
LH: Triggers ovulation and corpus luteum formation
Testosterone: Present in lower amounts, influences libido and energy
Prolactin: Involved in lactation, modulates sexual satisfaction
Oxytocin: Supports uterine contractions, milk ejection, and bonding

Clinical and Physiological Relevance

Menstrual irregularities (e.g., PCOS, amenorrhea) often reflect hormonal imbalances
Menopause marks the end of cyclical hormone production, leading to symptoms from estrogen/progesterone decline
Hormonal contraception modifies the natural cycle to prevent ovulation
Sleep, mood, and libido are all influenced by cyclical hormone changes