Corpus luteum function

Formation & Structure - The Yellow Body

• Post-ovulation transformation: The remnants of the ovarian follicle form the corpus luteum (CL).
• Luteinization: Triggered by the LH surge, granulosa and theca interna cells hypertrophy, accumulating a yellow pigment (lutein), giving it its name-"yellow body."
  • Granulosa lutein cells: Produce progesterone.
  • Theca lutein cells: Produce androgens & progesterone.
• Highly vascularized: Essential for hormone transport.

⭐ The LH surge is the critical trigger for both ovulation and the subsequent luteinization of follicular cells into the corpus luteum.

Hormonal Hub - Progesterone Power

• Primary Role: Luteal phase engine, primarily producing progesterone. Also secretes inhibin A and some estrogen.
• Progesterone's Core Functions:
  • Uterine Preparation: Converts endometrium to a secretory state, ready for implantation. ↑ glycogen, ↑ spiral artery growth.
  • Pregnancy Maintenance: Relaxes myometrium (prevents contractions) and thickens cervical mucus (forms a protective plug).
  • HPA Axis Suppression: Provides negative feedback to the hypothalamus and pituitary, ↓ GnRH, FSH, and LH. This prevents new follicle development.

⭐ The Luteal-Placental Shift: The corpus luteum is critical for maintaining pregnancy for the first 8-10 weeks by producing progesterone. After this period, the placenta becomes the primary source. Failure of this shift can result in miscarriage.

Fate of the Luteum - Live or Let Die

• The corpus luteum has two potential fates, determined by the presence or absence of fertilization.

1. No Fertilization (Luteolysis)

• If no fertilization occurs, the corpus luteum has a fixed lifespan of ~14 days.
• It degenerates into a fibrous scar tissue called the corpus albicans.
• This leads to a sharp ↓ in progesterone and estrogen, triggering endometrial breakdown and menstruation.

2. Fertilization Occurs (Luteal Rescue)

• The syncytiotrophoblast of the implanting blastocyst secretes human chorionic gonadotropin (hCG).
• hCG, an analog of LH, "rescues" the corpus luteum, which becomes the corpus luteum of pregnancy.

⭐ The corpus luteum is critical for progesterone production until the 8-10th week of gestation, when the placenta takes over this function (luteal-placental shift).

Clinical Correlations - Luteal Phase Lows

• Luteal Phase Defect (LPD):
  • Corpus luteum produces insufficient progesterone (↓ P4).
  • Results in a shortened luteal phase (< 12 days).
  • Causes inadequate endometrial maturation for implantation.
  • Clinically presents as infertility or recurrent early pregnancy loss.
• Premenstrual Syndrome (PMS) / PMDD:
  • Symptoms arise in the luteal phase due to hormonal shifts.
  • Not caused by abnormal hormone levels, but rather an abnormal response to normal levels.
  • PMDD is a severe form causing significant distress.

⭐ Luteal phase support with progesterone is a common intervention in assisted reproductive technology (ART) cycles to ensure endometrial receptivity.

High‑Yield Points - ⚡ Biggest Takeaways

• The corpus luteum forms from remnant granulosa and theca cells post-ovulation.
• Its primary role is secreting progesterone, which maintains the secretory endometrium for implantation.
• If fertilization occurs, hCG "rescues" the corpus luteum, sustaining progesterone output.
• Without pregnancy, it degenerates into the corpus albicans in 10-14 days.
• This subsequent progesterone withdrawal triggers menstruation.
• The placenta assumes progesterone production by weeks 8-10 of gestation.