Corpus Luteum
கார்பஸ் லூட்டியம்
The Graafian follicle does not simply vanish after ovulation. It undergoes a functional metamorphosis into the Corpus Luteum. Ignore this structure, and you fail to understand the hormonal basis of pregnancy.
The idea
Post-ovulation, the ruptured Graafian follicle transforms into the corpus luteum. This yellow endocrine body secretes large quantities of progesterone. Progesterone is essential for the maintenance of the endometrium, which is necessary for implantation of the blastocyst and other events of pregnancy.
Why it matters
It functions as a temporary endocrine gland to prepare the uterus for potential pregnancy by maintaining the uterine lining.
NEET lens
NEET focuses on the function of the corpus luteum and its hormonal output. Memorize that it secretes progesterone, not estrogen. Expect questions linking the luteal phase to the secretory phase of the uterine cycle. Do not confuse the corpus luteum with the Graafian follicle; they are sequential stages.
Clinical significance
If fertilization does not occur, the corpus luteum degenerates into the corpus albicans. This leads to a sharp decline in progesterone, triggering the shedding of the endometrium as menstrual flow. Luteal phase deficiency is a primary cause of early pregnancy loss.
Introduction
The corpus luteum ('yellow body') is a temporary endocrine gland formed from the ruptured Graafian follicle after ovulation, producing progesterone and estrogen to maintain the secretory endometrium and support early pregnancy.
Core concept
Formation: post-ovulation, granulosa cells and theca cells of ruptured follicle → luteinize (LH-driven) → fill with lipid droplets (yellow) → corpus luteum. Hormones: primarily progesterone + some estrogen. Functions: Prepares endometrium for implantation (secretory phase: glands, blood vessels, decidualization). Maintains progesterone to prevent menstruation. Supports early pregnancy (until placenta takes over ~Week 10). If no fertilization: corpus luteum degenerates after 14 days → corpus albicans (white scar) → progesterone falls → menstruation. If fertilization: hCG from blastocyst trophoblast (acts like LH) → rescues corpus luteum → maintains progesterone → pregnancy continues until placenta can produce own progesterone.
Go deeper
hCG rescue of corpus luteum: hCG (structurally similar to LH, same receptor) binds LH receptors on corpus luteum → prevents apoptosis → continued progesterone production. hCG appears at Day 8-9 (implantation) → peaks Week 10 → declines as placenta takes over. Without this rescue: corpus luteum degenerates Day 26-28 → menstruation even in pregnancy.
From Class 10
After ovulation, the empty follicle doesn't just disappear. It transforms into a temporary endocrine gland called the corpus luteum that produces hormones to support early pregnancy.