Full mechanism, in text

How the cycle works

1 · Two curves · two upstream signals

The cycle is a relay from hypothalamus to pituitary to ovary to endometrium: the pituitary releases and , and the ovary answers with and progesterone.The cycle is not the uterus performing alone — it is a hypothalamus → pituitary → ovary → endometrium relay. Upstream the pituitary releases and ; downstream the ovary answers with two main curves — (E2) and progesterone (P).

The x-axis is one standard 28-day cycle (counting from Day 1 of menses). Remember the shape of these two lines — the next three steps all happen on them.

2 · Follicular → ovulation (LH surge) → luteal

drives the follicle to grow, the peak triggers the surge and ovulation, then the corpus luteum secretes progesterone, whose withdrawal without implantation brings menstruation.Follicular (Day 1-13): ↑ → follicle grows + rises, endometrium proliferates (thickens).

Ovulation (Day 13-15): E2 peaks, positive feedback triggers the surge → ovulation within 24-36 h; basal body temperature then rises 0.3-0.5 °C.

Luteal (Day 15-28): the follicle collapses into the corpus luteum, secreting P + some E2; endometrium differentiates for implantation. Fixed at ~ 14 ± 2 days. No implantation → P withdrawal → endometrium sheds = menstruation.

3 · Which hormone each feeling maps to

Cycle sensations such as temperature, appetite, mood and sebum are not from nowhere: they hang on the and progesterone curves.Basal body temperature: luteal P ↑ → +0.3-0.5 °C (confirms ovulation, can't predict it).Energy + appetite: luteal energy intake on average ↑ 100-300 kcal/day, preference for carbs + high fat.Mood + sleep: late-luteal swings in the P metabolite allopregnanolone → ↓ + premenstrual mood sensitivity in some.Sebum: post-ovulation P ↑ → acne peak 3-5 days pre-menses.
Know which line is moving, and you know what the body is doing these days.

4 · Normal variation vs see-a-doctor

A normal cycle can run anywhere from 21 to 35 days, while cycles outside that range, abnormal bleeding or amenorrhea are signals to see a doctor."A normal cycle is 28 days" is a misconception. The luteal phase is fixed; almost all variation is in the follicular phase.

Ranges commonly used as normal (the FIGO 2018 classification judges frequency, regularity, period length and blood loss separately; the figures below are the ones commonly used in clinical practice)
Cycle length 21-35 days · period 2-7 days · blood loss 5-80 mLAdjacent cycles differ by ≤ 7-9 days
See gynaecology promptly (red flags, meaning preserved)
Cycle < 21 or > 35 days for ≥ 3 consecutive cyclesPeriod > 7 days; saturating 1 pad per hour, large clotsIntermenstrual or postcoital bleeding; any postmenopausal bleeding (rule out endometrial cancer first)Amenorrhea > 3 months (exclude pregnancy). Enduring it is not a virtue — quantify and check early.

Full mechanism, in text

1 · Two curves · two upstream signals

2 · Follicular → ovulation (LH surge) → luteal

3 · Which hormone each feeling maps to

4 · Normal variation vs see-a-doctor

The hormone tide · two curves in one cycle

Full mechanism, in text

1 · Two curves · two upstream signals

2 · Follicular → ovulation (LH surge) → luteal

3 · Which hormone each feeling maps to

4 · Normal variation vs see-a-doctor

The hormone tide · two curves in one cycle