Menstrual and Ovarian Cycle Phases and Hormonal Changes

The Menstrual and Ovarian Cycles

Menstruation: This phase begins on the first day of the cycle and lasts 5 to 7 days. If fertilization does not occur, the corpus luteum breaks down and stops producing progesterone. This causes the endometrium to shed, along with the oocyte, resulting in menstruation. If fertilization occurs, the embryo produces a hormone similar to LH (Luteinizing Hormone) to keep the corpus luteum active. It continues producing hormones, preventing menstruation. The oocyte is fertilized and completes oogenesis.

Proliferative Phase: This starts after menstruation and lasts until ovulation. Estrogens from the ovarian follicle stimulate the thickening of the endometrium and the growth of blood vessels.

Secretory Phase: This occurs after ovulation until the next period. Progesterone from the corpus luteum causes the endometrium to reach maximum thickness, preparing it for possible embryo implantation.

The Ovarian Cycle

• Follicular Phase (Days 0–14): The follicle grows thanks to FSH (Follicle-Stimulating Hormone) and produces estrogens.
• Luteal Phase (Days 15–28): The corpus luteum is formed in the ovary and secretes progesterone thanks to LH (Luteinizing Hormone).
• Ovulation (Day 14): The mature follicle is ruptured, and the egg is released into the Fallopian tubes (the woman is fertile) thanks to the highest levels of LH (Luteinizing Hormone).

The Menstrual Cycle

• Proliferative Phase: The endometrium starts to thicken thanks to estrogens.
• Secretory Phase: Maximum thickening of the endometrium occurs as it prepares for possible implantation of a fertilized egg thanks to progesterone.
• Menstruation: If fertilization has not taken place, the corpus luteum stops producing progesterone, and the endometrium breaks away.

Detailed Ovarian Cycle Timeline

• Menstruation (Days 1–5): The uterine lining is shed due to a drop in progesterone, releasing blood and tissue through the vagina.
• Follicular Phase (Days 1–14): FSH from the pituitary gland stimulates the growth of a follicle in the ovary. The maturing follicle produces estrogens.
• Ovulation (Day 14): High levels of LH cause the mature follicle to rupture, releasing the egg into the Fallopian tube. This is the fertile window.
• Luteal Phase (Days 15–28): The ruptured follicle becomes the corpus luteum, which secretes progesterone (stimulated by LH). If fertilization doesn’t occur, progesterone drops and menstruation begins again on day 28.