LH Surge
LH எழுச்சி
Do not confuse the LH surge with the estrogen peak. The surge is the trigger, not the result. If you miss this timing, you miss the entire reproductive cycle.
The idea
The LH surge is the rapid, massive secretion of Luteinizing Hormone reaching its peak concentration mid-cycle, specifically around day 14. This surge acts on the mature Graafian follicle. It induces the rupture of the follicular wall. Consequently, the secondary oocyte is released from the ovary, a process defined as ovulation.
Why it matters
It acts as the physiological trigger to ensure ovulation occurs precisely when the follicle is mature and ready for fertilization.
NEET lens
NEET asks this 9 times in the last decade. Focus on the timeline: it occurs mid-cycle. Do not confuse it with FSH; FSH peaks earlier. Remember: LH surge causes ovulation, not the other way around.
Clinical significance
Failure of the LH surge results in anovulatory cycles, a primary cause of female infertility. In clinical practice, we monitor this surge to time intrauterine insemination (IUI) or IVF procedures. Without this precise hormonal spike, the oocyte remains trapped within the follicle.
Introduction
The LH (Luteinizing Hormone) surge is a massive, brief spike in LH secretion from the anterior pituitary (~Day 13-14 of menstrual cycle) triggered by peak estrogen levels (positive feedback), which causes ovulation approximately 36 hours later.
Core concept
Mechanism: Rising estrogen from mature Graafian follicle → positive feedback on hypothalamus/anterior pituitary → massive GnRH pulse → LH surge (10-fold rise in LH). LH surge effects: (1) Resumes meiosis I in primary oocyte → secondary oocyte + first polar body. (2) Triggers prostaglandin production → follicle wall digestion. (3) Stimulates proteases → breakdown of follicle wall. (4) Ovulation: follicle ruptures → secondary oocyte released (~36 hours after LH peak). (5) Luteinization: granulosa cells → corpus luteum (under continued LH). LH detection: home ovulation predictor kits detect urinary LH surge → predicts ovulation 24-36 hours later.
Go deeper
Why positive feedback (unique)? During most of cycle, estrogen provides negative feedback (standard). Only at high estrogen concentration (peak of Graafian follicle) does the feedback switch to positive → ensures sharp, precisely timed LH surge → single ovulation event. This is one of the very few positive feedback endocrine systems in the body.
From Class 10
Ovulation — the release of an egg from the ovary — does not happen randomly. It is triggered by a specific hormonal signal called the LH surge.