Female Reproductive System and Embryogenesis

Flashcards covering the vocabulary and key physiological concepts of the female reproductive system, the menstrual/uterine cycles, fertilization, and sex determination.

Menstrual cycle

Regular periodic hormonal changes occurring approximately every $28$ days, starting with menstruation.

Ovulation

A prerequisite for fertilization occurring when one ova is released per cycle from the ovary.

Oogonia

Female germ cells whose number is fixed in utero, reaching approximately $2-4 \times 10^{6}$ clones during the first trimester.

Myometrium

The layer of smooth muscle occupying most of the uterus wall, responsible for important contractions during birth.

Perimetrium

The outer layer of the uterus composed of connective tissue and epithelial cells.

Endometrium

A layer of epithelial cells and a thick layer of connective tissue containing glands that secrete fluid to bathe the uterine lining.

Meiotic arrest

The suspension of oocyte meiosis characterized by decondensation of chromatin to support transcription; it can last up to $50$ years.

Ovarian follicle

The functional unit of the ovary that performs gametogenic and endocrine functions, containing a single developing ovum.

Primordial follicle

The earliest and simplest follicular stage, consisting of a developing oocyte surrounded by a single layer of specialized follicle cells.

Menarche

The occurrence of the very first menstrual cycle.

Menopause

The end of the menstrual cycle, occurring when fewer than $1000$ primordial follicles remain.

Follicular atresia

The death of follicles by apoptosis, affecting approximately $99.9$% of all follicles.

Granulosa cells

Epithelial cells that act as intermediaries between the oocyte and hormones; they secrete inhibin, transport nutrients via gap junctions, and manufacture progesterone.

Theca cells

Epithelioid cells forming a flattened layer around the follicle that express LH receptors and produce androgens like androstenedione.

Zona pellucida

A thick extracellular matrix of glycoproteins ($ZP1$, $ZP2$, and $ZP3$) that providing a species-specific binding site for sperm.

Antrum

A fluid-filled cavity that forms when spaces between granulosa layers coalesce during follicular development.

Mural granulosa cells

Basal layer granulosa cells adhered to the basal lamina that become highly steroidogenic and differentiate into the corpus luteum after ovulation.

Cumulus cells

Granulosa cells surrounding the oocyte that are released during ovulation and are crucial for oocyte capture by the oviduct.

Theca interna

The highly vascularized part of the theca layer that delivers hormones like $FSH$ and $LH$ and nutrients to the follicle.

Luteinization

The change in steroidogenic function of theca and mural granulosa cells that leads to the formation of a corpus luteum.

Corpus luteum

An endocrine structure formed after ovulation that produces large amounts of progesterone and estrogen; it degenerates into the corpus albicans if fertilization does not occur.

Menstrual phase

The phase of the uterine cycle where the outer layer of the endometrium dies and sheds due to falling levels of estrogen and progesterone.

Proliferative phase

The phase of the uterine cycle where the uterus renews itself, myometrium thickens, and glands enlarge, driven by increasing estrogen from the dominant follicle.

Secretory phase

The uterine phase where endometrial glands secrete glycogen-rich fluid and cervical mucus becomes viscous ('the plug') under the influence of progesterone.

Capacitation

The process sperm undergo to alter membrane fluidity and remove proteins/carbohydrates to facilitate the acrosome reaction.

Acrosome reaction

Triggered by sperm binding to $ZP3$, this reaction involves the fusion of sperm membranes to release enzymes that penetrate the zona pellucida.

Egg activation

The completion of the second meiotic division in the egg, triggered by an intracellular release of $Ca^{2+}$ upon fusion with sperm.

Syncytiotrophoblast

Trophoblast cells that secrete $hCG$ to rescue the corpus luteum and facilitate the transfer of gases and nutrients.

Decidualization

The maternal response to implantation where endometrial stroma transforms into enlarged, glycogen-filled cells that inhibit further embryo migration.

Placenta

A fetomaternal organ where fetal and maternal blood come into close proximity for the exchange of gases and nutrients without mixing.

srY gene

The sex-determining region on the $Y$ chromosome that produces testis-determining factor to instruct primitive gonads to become testes.

Mullerian inhibiting substance (MIS)

Also known as $AMH$, this glycoprotein produced by Sertoli cells causes the regression of the Mullerian ducts in males.

$$5\text{-}\text{alpha-reductase-2}$$

The enzyme responsible for the peripheral conversion of testosterone to dihydrotestosterone ($DHT$), necessary for male external genitalia differentiation.