Oogenesis and Follicle Development

Vocabulary terms and definitions regarding meiotic events and follicle development in the human ovary.

Oogonium

The stem cell ($2n$) that undergoes mitosis before birth to produce primary oocytes.

Primary oocyte

A diploid ($2n$) cell produced before birth that remains arrested in prophase I of meiosis throughout infancy and childhood.

Primordial follicle

The initial follicle stage present at birth containing a primary oocyte arrested in prophase I.

LH surge

The monthly hormonal trigger from puberty to menopause that causes one primary oocyte to complete meiosis I.

First polar body

A haploid cell produced along with the secondary oocyte during the completion of meiosis I; it ultimately degenerates.

Secondary oocyte

A haploid ($n$) cell produced by the completion of meiosis I that is arrested in metaphase II and released during ovulation.

Secondary follicle

A follicle stage containing a primary oocyte that is still arrested in prophase I.

Vesicular (antral) follicle

A mature follicle stage containing a secondary oocyte arrested in metaphase II.

Ovulation

The process where a secondary oocyte is released from a ruptured vesicular follicle.

Meiosis II completion

The specific stage of meiosis that occurs only if a sperm penetrates the secondary oocyte.

Ovum

The functional haploid ($n$) gamete produced after the completion of meiosis II following fertilization.

Second polar body

A haploid product of the completion of meiosis II that occurs after sperm penetration.

Corpus luteum

The structure formed from a ruptured follicle after ovulation that eventually degenerates if no pregnancy occurs.