Which covering of the ovum is present at the time of ovulation in humans?

Follicular development stages: Primordial follicle (oocyte + flat granulosa cells) → Primary follicle (cuboidal granulosa) → Secondary follicle (zona pellucida forms, antrum begins) → Graafian/Tertiary follicle (large antrum, corona radiata, cumulus oophorus). LH surge triggers ovulation of Graafian follicle.

Ovulation: LH surge (day 14 of 28-day cycle) → proteolytic enzymes digest follicle wall → oocyte released. Released as: secondary oocyte (2n, arrested in meiosis II metaphase) + zona pellucida + corona radiata. Captured by fimbriae of fallopian tube.

Sperm survival: 48-72 hours in female reproductive tract. Capacitation: sperm gain fertilisation capability in female tract. Acrosome reaction: triggered by ZP3 binding. Cortical reaction: prevents polyspermy. Meiosis II completion: triggered by fertilisation → mature ovum + second polar body.

Zona pellucida in ART (Assisted Reproductive Technology): IVF: sperm penetrates zona normally. ICSI: single sperm injected directly through zona into oocyte (for severe male infertility). Zona drilling/hatching: artificial opening of zona to improve implantation rates. Zona pellucida antibodies: can cause infertility (immune-mediated).

A primordial follicle contains an oocyte surrounded by a single layer of flat cells. It becomes a primary follicle when those cells turn cuboidal, then a secondary follicle as more layers form, and then a tertiary follicle once a fluid-filled antrum appears. The mature Graafian follicle has a large antrum and the oocyte sits on a stalk of cells called the cumulus oophorus. Only one follicle usually reaches this stage in each cycle; the rest undergo atresia.

After ovulation the ruptured follicle transforms into the corpus luteum, which secretes large amounts of progesterone. Progesterone maintains the thickened endometrium and is essential for implantation and for sustaining early pregnancy. If fertilisation does not occur the corpus luteum degenerates into the corpus albicans after about ten days, progesterone falls, and the endometrium is shed as menstruation. If pregnancy occurs, hCG from the embryo keeps it alive.

FSH drives follicular growth, and the growing follicle secretes oestrogen. Rising oestrogen triggers a sharp LH surge around day 14, and that surge causes ovulation. LH then maintains the corpus luteum, which secretes progesterone through the luteal phase. Knowing which hormone peaks when answers almost every graph-based question on this topic: oestrogen peaks just before ovulation, LH exactly at it, and progesterone about a week after.