Human Reproductive Systems and Embryonic Development

Vocabulary practice flashcards covering male and female reproductive anatomy, gametogenesis, the ovarian and uterine cycles, fertilization, and embryonic/fetal development.

Vulva (pudendum)

The collective anatomical term for the female external genitalia, functioning to protect internal reproductive structures, provide sensation, allow urination and sexual intercourse, and play a role in childbirth.

Perineum

The area of skin situated between the anus and the vulva in females (or scrotum in males).

Myometrium

The thick middle layer of smooth muscle in the uterine wall that contracts rhythmically during childbirth to expel the fetus.

Stratum functionalis (functional layer)

The mucosal inner layer of the endometrium that undergoes cyclic modifications in response to fluctuating ovarian hormone levels and sheds during menstruation.

Ampulla (fallopian tube)

The curved, lateral region of the fallopian tube where fertilization of an oocyte typically occurs.

Oogenesis

The biological process occurring within the ovaries that results in the formation and development of female gametes (oocytes).

Primary oocyte

A diploid ($2n$) female germ cell that begins meiosis I during fetal life and remains suspended in prophase I until stimulated after puberty.

Secondary oocyte

The haploid ($1n$) cell produced by the completion of meiosis I in a dominant follicle, arrested in metaphase II until fertilization triggers completion of meiosis II.

Corpus luteum

An endocrine glandular structure formed from the remnants of the ruptured follicle following ovulation that secretes progesterone and oestrogen.

Corpus albicans

The non-functional fibrous scar tissue formed within the ovary when the corpus luteum degenerates in the absence of fertilization.

Follicular phase

The first period of the ovarian cycle (days 0–14) characterized by follicle growth, oestrogen secretion, and culmination in ovulation.

Luteal phase

The second period of the ovarian cycle (days 15–28) defined by corpus luteum secretory activity and hormone production, which consistently lasts 14 days.

Proliferative phase

The pre-ovulatory phase of the uterine cycle (days 5–14) driven by ovarian estrogens, during which the stratum functionalis is rebuilt and cervical mucus thins to permit sperm entry.

Secretory phase

The post-ovulatory phase of the uterine cycle (days 15–28) where progesterone and estrogen stimulate endometrial glands to enlarge and secrete glycogen in preparation for blastocyst implantation.

Corpus cavernosum

Paired dorsal columns of erectile tissue in the penis that fill with blood and harden during an erection.

Corpus spongiosum

A single midventral column of erectile tissue surrounding the spongy urethra, functioning to keep the urethra open during erection and ejaculation.

Dartos muscle

A subcutaneous layer of smooth muscle in the scrotal wall that wrinkles and thickens the skin when contracted, reducing heat loss in cool environments.

Cremaster muscle

Skeletal muscle bands suspending the testes that contract to pull the scrotum and testes closer to the body core to maintain an optimal temperature of $34^\circ\text{C}$.

Testis

The primary male reproductive organ (gonad) divided internally into about 250 lobules containing seminiferous tubules, responsible for spermatogenesis and androgen synthesis.

Seminiferous tubules

Tightly coiled tubular structures within the testicular lobules that serve as the actual sites of sperm production.

Epididymis

A coiled, comma-shaped duct system capping the testis where immature, immotile sperm are stored, protected, and functionally matured over approximately 20 days until motile.

Ductus deferens (vas deferens)

A muscular conduit that ascends within the spermatic cord and propels mature sperm from the epididymis to the ejaculatory duct via peristalsis.

Seminal glands (seminal vesicles)

Accessory glands that secrete an alkaline, viscous fluid containing fructose, prostaglandins, and clotting proteins, constituting 60–70% of total semen volume.

Prostate gland

A doughnut-shaped gland encircling the prostatic urethra inferior to the bladder that secretes an activating fluid with citrate and enzymes, making up approximately 30% of semen volume.

Bulbourethral glands

Pea-sized accessory glands that produce a clear, thick alkaline mucus to neutralize residual acidic urine in the spongy urethra and lubricate the glans penis prior to ejaculation.

Spermatozoon

A mature male gamete consisting of a DNA-containing head capped by an acrosome, an energy-generating mitochondrial midpiece, and a propulsive flagellar tail.

Acrosome

A modified vesicle at the anterior tip of the sperm nucleus loaded with hydrolytic enzymes essential for digesting the outer protective layers of the oocyte.

Hypothalamic-pituitary-gonadal (HPG) axis

The neuroendocrine pathway comprising hypothalamic GnRH, anterior pituitary FSH and LH, and gonadal steroid hormones that regulates gametogenesis and sexual maturation.

Capacitation

A 2-to-10 hour physiological process occurring within the female reproductive tract that destabilizes the sperm's outer membranes, enabling acrosomal enzyme exocytosis.

Cortical reaction

The exocytosis of cortical granules from an oocyte triggered by sperm fusion, causing the zona pellucida to harden and destroy sperm receptors to block polyspermy.

Morula

A solid cluster of 16 or more blastomeres formed by early mitotic cleavage divisions without cellular growth, typically reached around day 3 after fertilization.

Blastocyst

A pre-embryonic fluid-filled spherical structure consisting of an outer trophoblast layer and an eccentric inner cell mass (embryoblast).

Syncytiotrophoblast

The multinucleated outer cellular mass of the trophoblast that aggressively digests endometrial tissue during implantation and secretes human chorionic gonadotropin (hCG).

Human chorionic gonadotropin (hCG)

A hormone produced by embryonic trophoblast cells that rescues and maintains the corpus luteum, sustaining progesterone and estrogen levels to prevent menstruation.

Gastrulation

The developmental rearrangement occurring around days 12–16 where the embryonic disc differentiates into the three primary germ layers.

Primary germ layers

The three primitive embryonic cell layers (ectoderm, mesoderm, and endoderm) derived from the epiblast that differentiate into all organ systems and tissues of the body.

Ectoderm

The outermost primary germ layer that gives rise to the nervous system, epidermis of the skin, hair, nails, and cutaneous glands.

Mesoderm

The middle primary germ layer that develops into bone, muscle, connective tissues, the cardiovascular system, kidneys, and gonads.

Endoderm

The innermost primary germ layer that forms the epithelial lining and associated glands of the respiratory and digestive tracts.

Amnion

A transparent membranous sac filled with fluid that surrounds and cushions the developing embryo, allowing symmetric growth and preventing physical distortion.

Chorion

The outermost extraembryonic membrane formed by trophoblast cells and mesoderm that encloses the embryo and all other membranes, forming the fetal contribution to the placenta.

Yolk sac

An extraembryonic membrane that contributes to the formation of the embryonic gut, serves as the earliest site of blood cell formation, and seeds primordial germ cells to the gonads.

Allantois

A small extraembryonic outpocketing of the posterior embryonic gut that forms the structural foundation and vascular base of the umbilical cord.

Placenta

A temporary fetomaternal organ that conducts gas, nutrient, and waste exchange, synthesizes pregnancy hormones, and keeps maternal and fetal blood supplies completely separate.