Reproductive Systems, Development, and Heredity

Comprehensive practice flashcards defining key anatomical structures, hormonal pathways, physiological mechanisms, developmental stages, and genetic inheritance patterns covered across Reproductive Systems I, II, III, and Embryology/Genetics lectures.

Gonads

The primary reproductive organs—specifically the ovaries in females and the testes in males—that produce gametes (sex cells) and secrete sex hormones.

Gametogenesis

The process of forming human sex cells (gametes), producing haploid secondary oocytes in females and haploid sperm in males via meiosis.

Gonadotropin-Releasing Hormone (GnRH)

A hormone secreted by the hypothalamus that triggers puberty by stimulating the anterior pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Synapsis

The pairing of homologous maternal and paternal replicated chromosomes during prophase I of meiosis to form a four-chromatid structure termed a tetrad.

Crossing Over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I, resulting in sister chromatids that are no longer genetically identical.

Reduction Division

The separation of homologous maternal and paternal pairs of replicated chromosomes to opposite poles of the cell during anaphase I, reducing the cell chromosome count from diploid ($46$ chromosomes) to haploid ($23$ replicated chromosomes).

Primordial Follicle

The most primitive type of ovarian follicle, containing a primary oocyte arrested in prophase I surrounded by a single flattened layer of follicle cells; approximately $1.5\text{ million}$ are present at birth.

Zona Pellucida

A protective glycoprotein layer directly surrounding the primary and secondary oocytes within developing ovarian follicles.

Corona Radiata

The innermost cellular layer of the cumulus oophorus immediately surrounding the zona pellucida of an oocyte.

Vesicular Follicle

A mature follicle containing a fluid-filled antrum and a secondary oocyte that has completed meiosis I and is arrested in metaphase II; typically only one matures fully each month.

Corpus Luteum

A temporary endocrine structure formed from remnants of the ruptured vesicular follicle that secretes high amounts of progesterone and estrogen to stimulate endometrial buildup for implantation.

Corpus Albicans

A nonfunctional, white connective tissue scar formed in the ovary when a corpus luteum regresses in the absence of fertilization.

LH Surge

A marked spike in luteinizing hormone released from the anterior pituitary, induced when the mature vesicular follicle secretes a threshold level of estrogen; directly triggers ovulation.

Menopause

The cessation of ovarian and menstrual cycles for at least $1\text{ year}$, typically occurring between the ages of $45\text{ and }55$, characterized by follicular depletion and halted estrogen and progesterone production.

Round Ligaments

Fibrous connective tissue bands that extend from the lateral margins of the uterus, traverse the inguinal canal, and anchor into the labia majora to help maintain uterine position.

Proliferative Phase

The period of the uterine cycle (days $6\text{ to }14$) during which the functional layer of the endometrium rapidly rebuilds under the influence of rising estrogen levels from developing follicles.

Secretory Phase

The phase of the uterine cycle (days $15\text{ to }28$) during which progesterone from the corpus luteum promotes vascularization and uterine gland development in preparation for embryo implantation.

Prolactin

A hormone produced by the anterior pituitary that promotes breast milk synthesis by stimulating the development and secretory activity of mammary gland alveoli.

Pampiniform Plexus

A venous network within the spermatic cord surrounding the testicular artery that cools warm arterial blood heading toward the testes to maintain optimal temperature for spermatogenesis.

Dartos and Cremaster Muscles

Smooth and skeletal muscles that contract in cool temperatures to elevate the testes toward the warm body wall and relax in warm temperatures to allow the testes to descend.

Interstitial Cells

Cells situated in the loose connective tissue between seminiferous tubules (Leydig cells) that synthesize and secrete testosterone when stimulated by luteinizing hormone (LH).

Sustentacular Cells

Non-dividing support cells (Sertoli cells) within the seminiferous tubules that form the blood-testis barrier, nourish developing sperm cells, and secrete androgen-binding protein (ABP) and inhibin.

Androgen-Binding Protein (ABP)

A binding protein produced by sustentacular cells under the stimulation of FSH that binds to testosterone, keeping androgen concentrations elevated within the seminiferous tubules.

Spermiogenesis

The final stage of spermatogenesis in which spherical, nonmotile spermatids undergo morphological transformations—including acrosome cap formation, mitochondrial localization, and flagellum development—to become mature spermatozoa.

Seminal Vesicles

Paired accessory glands on the posterior surface of the urinary bladder that produce a viscous, alkaline fluid containing fructose to nourish sperm and prostaglandins to widen the external os of the cervix.

Bulbourethral Glands

Paired pea-sized glands located in the urogenital diaphragm that secrete a clear, viscous, alkaline mucin to neutralize acidic urine residues in the spongy urethra and provide lubrication.

Erection

The stiffening and enlargement of the penis during the excitement phase, mediated by parasympathetic release of nitric oxide that dilates central arteries, engorges venous spaces of the corpora cavernosa and corpus spongiosum, and compresses draining veins.

Capacitation

A physiological conditioning process undergone by sperm inside the female reproductive tract that alters their membrane and activates the acrosome cap, enabling fertilization of a secondary oocyte.

Cleavage

A sequence of rapid mitotic divisions occurring from $30\text{ hours}$ to day $3$ post-fertilization, increasing cell number without increasing the overall diameter of the pre-embryo.

Morula

A solid multicellular ball of $16$ or more cells formed by days $3\text{--}4$ post-fertilization that maintains the same overall diameter ($120\,\mu\text{m}$) as the original zygote.

Blastocyst

A hollow fluid-filled pre-embryonic sphere formed by days $5\text{--}6$ consisting of an outer trophoblast layer that forms extraembryonic membranes and an inner embryoblast that forms the embryo proper.

Human Chorionic Gonadotropin (hCG)

A hormone produced by syncytiotrophoblast cells during the first trimester that maintains the corpus luteum, preventing its degeneration and ensuring continued estrogen and progesterone secretion.

Placenta

A highly vascular organ that facilitates nutrient, gas, and metabolic waste exchange between maternal and fetal blood, provides passive immunity via maternal antibodies, and secretes estrogen and progesterone.

Gastrulation

A critical developmental process occurring during week $3$ of the embryonic period that establishes the three primary germ layers (ectoderm, mesoderm, and endoderm) and the notochord.

Teratogen

Any environmental substance, such as alcohol, tobacco, certain drugs, or viruses, that disrupts prenatal development and causes birth defects or embryonic/fetal death, particularly during weeks $3\text{--}8$.

Vernix Caseosa

A protective, cheese-like, fatty secretion that covers the fetal skin during weeks $17\text{--}20$ to shield it from amniotic fluid maceration.

Lanugo

A fine, downy, unpigmented hair coat that develops over the fetal skin during weeks $17\text{--}20$ to help hold vernix caseosa against the body.

Lochia

A postpartum vaginal discharge composed of blood, mucus, and sloughed uterine tissue that is discharged for several weeks following childbirth as the uterus heals.

Karyotype

A photographic display of an individual's complete set of chromosomes arranged in homologous pairs according to size, banding patterns, and centromere location.

Incomplete Dominance

An inheritance pattern in which a heterozygous individual displays an intermediate phenotype between homozygous dominant and homozygous recessive phenotypes, such as sickle cell trait.

Codominance

A pattern of inheritance in which two different alleles are equally dominant and both are fully expressed in the phenotype, as observed in $AB$ blood type ($I^A I^B$).

Polygenic Inheritance

The interaction of multiple independent genes located on the same or different chromosomes to determine a single continuous phenotypic trait, such as height and skin pigmentation.