Puberty begins in the hypothalamus, a small but powerful region in the brain. At the start of puberty, the hypothalamus becomes more active and starts releasing GnRH (gonadotropin-releasing hormone) in pulses.

These pulses are key. In childhood, GnRH release is almost silent. But at puberty, the pulses increase in frequency and amplitude, signaling the start of reproductive function.

2. Signal to the Pituitary – Hormonal Relay

GnRH travels to the pituitary gland, located just beneath the brain. It stimulates the release of two essential hormones:

FSH (follicle-stimulating hormone)

LH (luteinizing hormone)

These are called gonadotropins because they target the gonads, which are the ovaries in girls.

3. Ovarian Activation – Estrogen Production Begins

FSH and LH signal the ovaries to begin two main processes:

Follicular development: A group of immature egg-containing follicles begin to mature.

Estrogen secretion: The cells around the growing follicles start producing estrogen.

Estrogen is the key hormone responsible for most of the physical changes seen during puberty.

4. Systemic Effects of Estrogen

Once estrogen enters the bloodstream, it binds to estrogen receptors in various tissues throughout the body. This leads to multiple changes:

Breast development: Growth of ductal tissue in the breasts begins.

Uterine growth: The uterus increases in size and begins cycling.

Vaginal maturation: The lining of the vagina thickens and becomes more acidic.

Fat distribution: Body fat begins to accumulate in areas like the hips, thighs, and chest.

Bone growth and fusion: Estrogen accelerates long bone growth and later causes the closure of growth plates.

5. Adrenarche – Separate But Overlapping Process

Before or during early puberty, the adrenal glands begin producing androgens (like DHEA and androstenedione). This is called adrenarche and it contributes to:

Pubic and underarm hair

Body odor

Slight changes in mood and skin (acne)

Adrenarche is separate from the GnRH-driven process but often overlaps with it.

6. Menarche – The First Menstrual Cycle

As estrogen and progesterone levels rise and cycle, the uterus begins to prepare for potential pregnancy. The inner lining (endometrium) thickens under the influence of estrogen, and if no fertilization occurs, the lining is shed—this is the first period, or menarche.