Fertilization and Implantation

Vocabulary practice flashcards covering the hormonal regulation, follicular development, ovulation, fertilization, early cleavage, and implantation stages in human reproduction.

Ovulation

The process by which a mature egg is released from the ovary, pushed down the fallopian tube, and made available to be fertilized.

Gonadotropin-releasing hormone (GnRH)

A hormone produced by neurosecretory cells in the hypothalamus and transported via the hypophysial portal system to stimulate the anterior pituitary gland to release FSH and LH.

Follicle-stimulating hormone (FSH)

A gonadotropic hormone released by the anterior pituitary gland that promotes follicular development and stimulates the graafian follicle to mature and produce estrogens.

Luteinizing hormone (LH)

A gonadotropic hormone released by the anterior pituitary gland; an LH surge on the $13\text{th}$ day of the cycle triggers ovulation and induces the formation of the corpus luteum.

Theca folliculi

A capsule formed by adjacent connective tissue around an enlarging primary follicle, which differentiates into two layers: the theca interna and theca externa.

Antrum

A single large cavity containing follicular fluid, formed by the coalescence of fluid-filled spaces around follicular cells in a secondary follicle.

Cumulus oophorus

A mound of follicular cells that surrounds the primary oocyte after it has been pushed to one side within the growing secondary follicle.

Corpus luteum

An endocrine structure formed from the ruptured follicle following ovulation that secretes progesterone and estrogens to prepare the endometrium for blastocyst implantation and inhibit uterine contractions.

Corpus albicans

A white body or scar formed by the degeneration of the corpus luteum when fertilization does not occur and progesterone levels drop.

Syncytiotrophoblast

The outer embryonic layer that produces human chorionic gonadotropin (hCG), which keeps the corpus luteum active to maintain progesterone and estrogen secretion during pregnancy.

Stigma

A small avascular spot appearing on the ovarian swelling at midcycle that ruptures during ovulation under the influence of the LH surge to expel the secondary oocyte.

Corona radiata

One or two layers of follicular cells arranged radially around the expelled oocyte and zona pellucida.

Zona pellucida

A glycoprotein membrane surrounding the oocyte that is penetrated by sperm enzymes during fertilization and subsequently becomes impermeable to prevent polyspermy.

Sperm capacitation

The conditioning process occurring prior to fertilization wherein the glycoprotein coat and seminal plasma proteins are removed from the spermatozoon head.

Acrosome reaction

The process wherein perforations in the acrosome wall release acrosin and trypsin-like substances to digest and penetrate the zona pellucida.

Ootid

The penetrated oocyte following sperm entry that contains both the male and female pronuclei prior to their fusion.

Zygote

A single diploid cell containing $46$ chromosomes formed by the fusion of male and female pronuclei.

Compaction

The morphological change occurring after the $3\text{rd}$ cleavage division in which blastomeres maximize contact with each other to form a compact ball of cells.

Morula

A solid, mulberry-like cluster of $16$ blastomeres formed approximately $3$ days after fertilization.

Trophoblast

The outer cell mass of the blastocyst that gives rise to the placenta and attaches to the endometrial epithelium during implantation.

Embryoblast

The inner cell mass located at one pole of the blastocyst that gives rise to the embryo proper and represents a source of nearly pluripotent stem cells.

Blastocele

The central, fluid-filled cavity of the blastocyst that forms as fluid accumulates in the conceptus approximately $4\text{ to }5$ days after fertilization.

Basal layer (Basalis)

The thin deepest zone of the uterine endometrium that is retained during menstruation to regenerate the endometrium when fertilization does not occur.

Ampulla (of the uterine tube)

The anatomical region of the fallopian tube where fertilization of the secondary oocyte normally occurs.

Fimbriae

Fingerlike projections of the uterine tube infundibulum that sweep back and forth over the ovary to capture the expelled secondary oocyte.