Oogenesis, Folliculogenesis, and Fertilization

Comprehensive vocabulary flashcards covering ovarian histology, folliculogenesis, oogenesis phases, meiotic arrest points, fertilization steps, and reproductive physiology.

Medullary region (Medulla)

The internal region of the ovary containing blood vessels and ovarian follicles at different developmental stages.

Cortical region (Cortex)

The external region of the ovary covered by epithelium where oogenesis and follicular maturation occur.

Ovarian follicle

A functional ovarian unit consisting of an oocyte surrounded by follicular cells.

Primordial follicle

The earliest follicular stage ($30\,\mu\text{m}$) containing a primary oocyte (oocyte I) arrested at prophase I surrounded by a few flattened follicular cells.

Primary follicle

A growing follicle ($50\,\mu\text{m}$) containing a primary oocyte (oocyte I) surrounded by a single cuboidal layer of follicular cells.

Secondary follicle

An ovarian follicle ($100\,\mu\text{m}$) containing a primary oocyte (oocyte I) surrounded by multiple layers of follicular cells containing small cavities.

Cavitary follicle (Tertiary follicle)

An ovarian follicle ($300\,\mu\text{m}$ to $5\,\text{mm}$) containing a primary oocyte (oocyte I), many layers of follicular cells, and a large fluid-filled cavity known as the antrum.

Antrum (Follicular cavity)

The fluid-filled cavity that forms within a cavitary (tertiary) follicle and reaches maximum size in a mature Graafian follicle.

Graafian follicle

The mature ovarian follicle (measuring approximately $20\,\text{mm}$) containing an oocyte II, which bursts at ovulation to release the secondary oocyte into the pavilion.

Cumulus oophorus

A cluster of follicular cells (granulosa) that surrounds and attaches the oocyte to the wall of the Graafian follicle.

Corona radiata

The outermost protective layer of pedunculated follicular cells linked by a viscous substance that surrounds the oocyte II upon release.

Zona pellucida

The thick glycoprotein envelope located between the oocyte plasma membrane and the corona radiata that is digested by sperm acrosomal enzymes during fertilization.

Corpus luteum (Yellow body)

The endocrine structure formed from the ruptured Graafian follicle after ovulation; it persists during the first $3\,\text{months}$ of pregnancy if fertilization occurs, or degenerates into a white body by the end of the menstrual cycle if unfertilized.

Corpus albicans (White body)

The whitish scar tissue formed by the complete degeneration and regression of the corpus luteum in the absence of fertilization.

Folliculogenesis

The entire developmental progression of ovarian follicles that begins during fetal life, halts before puberty, and cyclically resumes from puberty until menopause.

Follicular atresia

The natural degenerative breakdown and loss of ovarian follicles that occurs during embryonic life, childhood, and throughout reproductive life.

Oogenesis

The biological process in the ovarian cortex through which diploid oogonia develop into haploid female gametes (ova) via multiplication, growth, maturation, and differentiation phases.

Oogonia

Diploid ($2n$, 2 chromatids) undifferentiated female germ cells that multiply through repeated mitotic divisions during embryonic life.

Primary oocyte (Oocyte I)

A diploid ($2n$, 2 chromatids) cell formed by the growth and DNA duplication of an oogonium that begins meiosis I and remains arrested at prophase I until puberty.

Secondary oocyte (Oocyte II)

A large, spherical, non-motile haploid ($n$, 2 chromatids) female cell produced by meiosis I that retains most of the cytoplasm, remains arrested at metaphase II, and survives for $24\,\text{hours}$ if unfertilized.

First polar body

A small haploid ($n$, 2 chromatids) cell with minimal cytoplasm formed alongside the secondary oocyte during the first meiotic division.

Second polar body

A tiny haploid ($n$, 1 chromatid) cell extruded by the secondary oocyte upon completing meiosis II, triggered by the entry of a fertilizing sperm cell.

Ootid

The haploid ($n$, 1 chromatid) female gamete stage resulting from the second meiotic division after sperm entry, prior to pronuclear fusion.

Menopause

The permanent biological cessation of menstrual cycles resulting from the total depletion of viable oocytes in the ovaries.

Ovulation

The release of an oocyte II blocked at metaphase II from the ruptured Graafian follicle into the pavilion of the oviduct around day $14$ of the ovarian cycle.

Fertilization

The union of two haploid ($n = 23$) gametes—a sperm cell and an ovum—in the oviduct to create a diploid zygote ($2n = 46$).

Sperm capacitation

Biochemical changes in the sperm plasma membrane that take place within the female reproductive tract, granting spermatozoa the capacity to fertilize for up to $48\,\text{hours}$.

Acrosomal reaction

The enzymatic digestion of the zona pellucida facilitated by proteases (including pepsin and trypsin) released from the sperm acrosome.

Cortical reaction

The release of cortical granules by exocytosis upon sperm entry to establish a fertilization membrane and prevent polyspermy.

Karyogamy

The fusion of the male and female pronuclei, during which their nuclear envelopes rupture and parental chromosomes mix together to initiate the first mitotic cleavage of the zygote.

Germ cells

Specialized reproductive cells located within the gonads (testes and ovaries) that undergo meiosis to generate haploid gametes.

Leydig cells

Endocrine cells located in the interstitial space between seminiferous tubules that synthesize and secrete testosterone.

Sertoli cells

Supporting somatic cells located inside the seminiferous tubules between developing germ cells that sustain and nourish them throughout spermatogenesis.