The moment of human ovulation was first filmed by accident in 2008
Nobody had ever filmed a human egg leaving its follicle until 2008, when a gynaecologist performing a routine hysterectomy happened to catch it on camera. The egg emerged and was released within about 15 minutes. The event is usually invisible for another reason too: humans, unlike many animals, show almost no outward signal of fertility.
The process runs on a hormonal relay. The hypothalamus in the brain directs the pituitary gland, which releases follicle-stimulating hormone and luteinising hormone. As a follicle matures, rising oestrogen triggers, by positive feedback, a surge of both hormones lasting 24 to 36 hours. That surge prompts enzymes to break down tissue at one spot on the follicle's wall, opening a hole called the stigma. The egg slips through, is swept up by finger-like fringes at the end of the fallopian tube, and tiny beating hairs push it toward the uterus.
The egg does not travel alone. It is wrapped in a sticky, hyaluronic-acid-rich cloud of support cells, and that coating turns out to be necessary for fertilisation. The egg has already completed its first meiotic division, producing a large cell and a small inert polar body, and its second division pauses halfway until a sperm arrives. Without fertilisation it degenerates within 12 to 24 hours. About 1 to 2 per cent of ovulations release more than one egg, a tendency that grows with age; two eggs fertilised by two sperm produce fraternal twins.
Timing varies more than the textbook 28-day diagram suggests. On average ovulation comes 14.6 days after a period begins, but the normal range stretches from about 8 to 20.5 days. The emptied follicle becomes the corpus luteum, a hormone factory whose progesterone raises resting body temperature by a quarter to half a degree Celsius. Some women notice changes in cervical mucus, a heightened sense of smell or a twinge of midcycle pain called Mittelschmerz, and charting such signs underpins fertility awareness methods.
Other species do things differently. In some animals, mating itself triggers ovulation. In humans, combined hormonal contraceptives work mainly by suppressing the pituitary hormones so ovulation never happens, while the most common cause of ovulation problems is polycystic ovary syndrome.
Source: Ovulation
