Menstruation: Physiology, Symptoms, and Lifespan

Menstruation = cyclic shedding of the functional endometrial layer triggered by progesterone withdrawal after failed implantation.

Cycle Phases

• Menstrual (days 1–5): bleeding.
• Proliferative (days 6–14): estrogen-driven endometrial regrowth.
• Ovulation (day ~14): LH surge.
• Secretory (days 15–28): progesterone stabilizes endometrium.

Normal Parameters

• Cycle length: 21–35 days.
• Bleeding duration: 2–7 days.
• Volume: 30–80 mL.
• Menarche: 10–15 yr (avg 12.4).
• Menopause: 45–55 yr (avg 51).

Common Symptoms

• Cramping (prostaglandin-mediated uterine contractions).
• Mood changes, bloating, breast tenderness, headache, fatigue.

Red Flags

• Amenorrhea >3 cycles (not pregnant).
• Heavy bleeding (>80 mL or >7 days).
• Intermenstrual bleeding.
• Severe pain unresponsive to NSAIDs.

Track cycles; seek evaluation for deviations.