Gametogenesis, Fertilization, and Early Embryonic Development

Vocabulary practice flashcards covering female and male gametogenesis, follicle maturation stages, sperm structure, semen clinical conditions, fertilization mechanisms, and early embryonic cleavage.

Primordial germ cells (Female)

Cells that line the ovaries in the $3^{\text{rd}}\text{ month}$ of intrauterine life inside the uterus and undergo mitosis to form oogonia.

Oogonia

Cells formed from mitotic division of primordial germ cells; they undergo an additional mitotic division up to the $7^{\text{th}}\text{ month}$ of intrauterine life to transform into primary oocytes.

Primordial follicle

A structure consisting of a primary oocyte surrounded by a single layer of flat cells, in which the oocyte undergoes only the first meiotic division and stops; about $6\text{--}8\text{ lakhs}$ are present at birth, with $500\text{--}600$ remaining alive at puberty.

Primary follicle

A developing ovarian follicle formed at puberty when pituitary FSH causes the primary oocyte to enlarge and the surrounding flat cells of the primordial follicle to become cuboid.

Secondary ($2^\top$) follicle

A follicle formed when the single layer of cuboid cells multiplies into multiple layers surrounding the oocyte.

Granulosa cells

The multiple layers of follicle cells surrounding the oocyte that accumulate fluid and participate in hormone secretion.

Tertiary ($3^\top$) follicle

A follicle characterized by fluid accumulation inside the granulosa cells under the influence of FSH secreted by the pituitary.

Graafian follicle

A mature ovarian follicle containing fluid rich in estrogen; this fluid provides negative feedback to the pituitary to decrease FSH while stimulating the release of LH.

Zona pellucida

A tough glycoprotein coat formed around the ovum (secondary oocyte).

Ovulation

The release of the ovum surrounded by the zona pellucida and granulosa cells into the pelvic cavity caused by excess fluid pressure rupturing the Graafian follicle.

Corona radiata

The protective radiating layer of granulosa cells that remains attached to and surrounds the ovum after ovulation.

Corpus luteum

A temporary endocrine structure formed from granulosa cells of the ruptured follicle filled with fat; it secretes high amounts of progesterone to establish a vascularized, multi-layered endometrial bedding for the incoming embryo.

Corpus albicans

The fibrosed, inactive scar tissue formed from the degeneration of the fat-filled corpus luteum when pregnancy does not occur.

Ampulla

The widest part of the fallopian tube to which the secondary oocyte is transported after being picked up by finger-like projections, serving as the site of fertilization.

Acrosomal cap

A specialized cap located on the head of a sperm containing digestive enzymes required to penetrate the ovum's outer layers.

Acrosin and hyaluronidase

Acrosomal enzymes released by the sperm head that digest and bore a hole through the zona pellucida.

Fertilization

The fusion of the haploid male gamete (sperm) and female gamete (ovum) inside the zona pellucida to form a diploid zygote.

Prevention of polygamy (polyspermy)

A post-fertilization effect wherein the zona pellucida immediately becomes impermeable to all other sperms once the head of one sperm penetrates.

Primordial germ cells (Male)

Germ cells in the testes that undergo mitosis at puberty to form spermatogonia, each giving rise to two primary spermatocytes.

Spermiogenesis

The developmental maturation process involving the conversion of immature spermatids into mature spermatozoa (sperms).

Spermiation

The physiological process by which mature spermatozoa are released from inside the seminiferous tubules.

Head of sperm

An anterior sperm compartment measuring $4\,\mu\text{m}$ that contains a condensed nucleus and an acrosomal cap housing acrosin and hyaluronidase enzymes.

Neck of sperm

A intermediate segment measuring $0.4\,\mu\text{m}$ containing thick filaments surrounding the central axial filament that continues into the body.

Body of sperm

A sperm segment measuring $4\,\mu\text{m}$ consisting of a central axial filament surrounded by nine filaments and mitochondria.

Tail of sperm

A flagellar segment measuring $35\text{--}36\,\mu\text{m}$ containing only the central axial filament, which propels the sperm while remaining outside during fertilization.

Capacitation

The activation process inside the uterine cavity where seminal fluid and the glycoprotein coat covering the sperm head are removed, enhancing sperm motility.

Normal sperm count

A standard clinical parameter defined as $15\text{ million per ml}$ of semen.

Oligozoospermia

A condition characterized by a sperm concentration of less than $15\text{ million per ml}$ of semen.

Azoospermia

The complete absence of sperms in semen.

Aspermia

The complete absence of semen ejaculation.

Asthenozoospermia

A semen pathology characterized by sperms exhibiting poor motility.

Teratozoospermia

A semen disorder where more than $10\%$ of sperms exhibit abnormal morphology.

Blastomere

Small individual cells formed as the diploid zygote undergoes repeated mitotic cleavage ($2\text{-celled}$, $4\text{-celled}$, and $8\text{-celled}$ stages).

Morula

A solid $16\text{-celled}$ embryo enclosed within the zona pellucida formed within $90\text{ hours}$ of fertilization.

Blastocyst

A developmental stage resulting from the accumulation of fluid within the morula while still enveloped by the zona pellucida.