The simple idea (no memorising)
Usually, estrogen tells the brain "ease off" — that's negative feedback. But there's a twist. When the dominant follicle makes estrogen that is high enough for long enough, the message flips to "go!" — positive feedback. The pituitary answers with a huge, brief burst of LH: the LH surge.
The trap everyone falls into
The LH surge is not the same as ovulation. The surge is the trigger; ovulation is the result, arriving roughly 32–36 hours later. So if someone asks, "What actually causes ovulation?" the answer is: the LH surge.
What happens in the moment of ovulation
Two things happen together:
- the egg (now a secondary oocyte) is released;
- the emptied follicle begins turning into the corpus luteum.
Why it matters
This is the hinge of the whole cycle, and the single most tested moment in it. It's also deeply practical: home ovulation kits work by detecting exactly this LH surge in urine, telling a couple that the fertile window has opened.
Quick check ✅
- What flips estrogen from a "calm down" signal to a "go!" signal?
- True or false: the LH surge and ovulation happen at the same instant.
Remember this 🌟
Where we're going next → The follicle is now empty. What does it become, and why does that matter so much? Concept 10.