Reproductive Systems, Embryonic Development, and Heredity

Comprehensive vocabulary flashcards covering the male and female reproductive systems, gametogenesis, menstrual and ovarian cycles, prenatal development, pregnancy endocrinology, and human heredity patterns.

Dartos muscle

A layer of smooth muscle within the scrotal wall that contracts when cold to reduce scrotal surface area and relaxes when warm to facilitate cooling of the testes.

Cremaster muscle

A skeletal muscle layer originating from the internal oblique muscle within the cremasteric fascia that contracts to elevate the testes toward the body or relaxes to lower them for thermoregulation.

Pampiniform plexus

A specialized network of testicular veins surrounding the testicular artery in the spermatic cord that cools warm arterial blood before it reaches the testes.

Tunica albuginea (testis)

A thick, white fibrous capsule covering the testis that projects internal septa to subdivide the testis into approximately 250 lobules.

Interstitial cells

Endocrine cells located in the spaces between seminiferous tubules that synthesize and secrete testosterone in response to luteinizing hormone (LH).

Sustentacular cells

Nonreplicating helper cells within seminiferous tubules that create the blood-testis barrier, provide nutrients to germ cells, and secrete androgen-binding protein (ABP) and inhibin.

Androgen-binding protein (ABP)

A binding protein secreted by sustentacular cells under FSH stimulation that binds testosterone to maintain elevated local levels inside the seminiferous tubules.

Spermiogenesis

The final stage of male gametogenesis wherein round haploid spermatids undergo morphological transformation into mature, motile spermatozoa by discarding excess cytoplasm, developing an acrosome cap, forming a flagellum, and condensing mitochondria into the midpiece.

Acrosome cap

A specialized enzymatic structure derived from the Golgi apparatus that caps the anterior sperm nucleus and contains digestive enzymes required to penetrate an oocyte.

Epididymis

A comma-shaped structure situated along the posterior border of each testis, composed of a head, body, and tail, that stores sperm and allows them to achieve motility.

Ductus deferens

A thick-walled muscular tube with smooth muscle layers that propels mature sperm from the epididymis toward the ejaculatory duct via peristalsis.

Seminal vesicles

Paired accessory glands on the posterior surface of the urinary bladder that secrete an alkaline fluid containing fructose for sperm nourishment and prostaglandins to promote cervical dilation.

Prostate gland

A compact accessory gland located immediately inferior to the bladder that secretes a milky, slightly acidic fluid containing citric acid, seminalplasmin antibiotic, and enzymes to liquefy coagulated semen.

Bulbourethral glands

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

Refractory period (male)

A physiological phase immediately following ejaculation and resolution in which a male cannot achieve another erection or orgasm, lasting from minutes to hours.

LH surge

A dramatic spike in luteinizing hormone secretion provoked by threshold-exceeding estrogen levels from the vesicular follicle that triggers the completion of meiosis I and induces ovulation.

Corpus luteum

A temporary endocrine structure formed from remnants of the ruptured mature follicle that secretes high amounts of progesterone, moderate estrogen, and inhibin to prepare the uterine lining.

Corpus albicans

A dense, white scar of connective tissue formed when the corpus luteum degenerates following a lack of fertilization and hCG signaling.

Menstrual phase

Days 1 to 5 of the uterine cycle during which the functional layer of the endometrium detaches and sloughs off as menstrual flow due to low ovarian hormone levels.

Proliferative phase

Days 6 to 14 of the uterine cycle during which rising estrogen levels stimulate basal cells to rebuild and vascularize the functional layer of the endometrium.

Secretory phase

Days 15 to 28 of the uterine cycle wherein progesterone from the corpus luteum stimulates endometrial gland development and nutrient-rich glycogen secretion in preparation for implantation.

Menopause

The permanent cessation of menstruation, clinically defined as 1 full year without menstrual cycles in the absence of pregnancy or disease, typically occurring between ages 45 and 55.

Round ligaments of the uterus

Paired fibrous cords extending from the lateral uterus through the inguinal canals to insert onto the labia majora, anchoring the uterus anteroinferiorly.

Transverse cervical ligaments

Fibrous bands that extend laterally from the cervix and superior vagina to the lateral pelvic walls, resisting downward movement of the uterus.

Prolactin

An anterior pituitary hormone whose secretion is stimulated by infant suckling that promotes alveolar growth and the synthesis of breast milk in mammary glands.

Oxytocin

A peptide hormone produced by the hypothalamus and released by the posterior pituitary that stimulates myometrial contractions during labor and myoepithelial contractions for milk ejection.

Gametogenesis

The biological process of forming haploid sex cells ($n = 23$) through meiosis, termed spermatogenesis in males and oogenesis in females.

Gonadotropin-releasing hormone (GnRH)

A neurohormone secreted by the hypothalamus that initiates puberty by stimulating the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Synapsis

The pairing and alignment of homologous maternal and paternal replicated chromosomes during prophase I of meiosis to form tetrads.

Crossing over

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis, creating novel combinations of alleles.

Reduction division

The separation of maternal and paternal homologous chromosome pairs during anaphase I of meiosis that reduces the chromosome ploidy from diploid ($2n = 46$) to haploid ($n = 23$).

Primordial follicle

The most primitive ovarian follicle type, containing a primary oocyte arrested in meiotic prophase I enclosed by a single layer of flattened follicle cells; roughly 1.5 million exist at birth.

Primary follicle

An ovarian follicle consisting of a primary oocyte surrounded by one or more layers of cuboidal granulosa cells and external thecal cells.

Secondary follicle

A developing ovarian follicle containing a primary oocyte surrounded by multiple granulosa cell layers, thecal layers, an early fluid-filled antrum, and a protective zona pellucida.

Corona radiata

The innermost layer of columnar granulosa cells immediately surrounding the zona pellucida of an ovulated secondary oocyte.

Atresia

The degenerative process through which non-selected ovarian follicles regress and resorb rather than completing maturation to ovulation.

Pre-embryonic period

The initial two weeks of human prenatal development spanning fertilization, cleavage divisions, and the complete implantation of the blastocyst into the endometrium.

Capacitation

The physiological conditioning that sperm undergo within the female reproductive tract that alters their acrosomal membrane permeability and activates their hypermotility.

Morula

A solid sphere composed of 16 or more blastomeres formed by day 3 to 4 post-fertilization that maintains the same total diameter as the original zygote ($120\,\mu\text{m}$).

Blastocyst

A hollow sphere of cells formed by days 5 to 6 of development that features an outer trophoblast layer, an inner fluid-filled cavity, and an inner cell mass called the embryoblast.

Trophoblast

The outer ring of epithelial cells of the blastocyst that participates in endometrial implantation and forms the fetal contributions of the placenta.

Embryoblast

The tightly clustered group of pluripotential cells situated internally at one pole of the blastocyst that differentiates into the embryo proper.

Human chorionic gonadotropin (hCG)

A hormone produced by syncytiotrophoblast cells that maintains the viability and progesterone production of the corpus luteum for the first three months of pregnancy.

Embryonic period

The developmental interval extending from week 3 through week 8 post-fertilization during which gastrulation, organogenesis, and embryonic folding establish rudimentary organ systems.

Teratogen

Any external agent—such as alcohol, nicotine, specific pharmacological drugs, radiation, or viruses—capable of causing structural malformations or death in an embryo or fetus.

Gastrulation

The critical developmental morphogenetic movement occurring during week 3 that reorganizes the embryonic disc into three primary germ layers: ectoderm, mesoderm, and endoderm.

Notochord

A cellular rod that develops along the longitudinal axis during gastrulation to establish body directionality (cranial-caudal) and guide tissue segmentation.

Fetal period

The period of prenatal development spanning week 9 through delivery (roughly 38 weeks total) focused on cellular differentiation, rapid skeletal ossification, and functional body growth.

Human placental lactogen (hPL)

A placental hormone that enhances maternal lipolysis to spare circulating glucose for fetal nutrition, which can contribute to maternal insulin resistance.

Incomplete dominance

A non-Mendelian genetic inheritance pattern where heterozygous individuals display an intermediate phenotype between the homozygous dominant and homozygous recessive conditions, such as the sickle cell trait.

Codominant inheritance

A genetic inheritance pattern in which two distinct alleles are equally dominant, resulting in the simultaneous, full phenotypic expression of both alleles, as seen in the $I^A$ and $I^B$ alleles of the ABO blood system.

Polygenic inheritance

The cumulative phenotypic outcome resulting from the additive interaction of multiple independent genes across one or more chromosomes, accounting for continuous traits such as height and skin color.

Sex-linked traits

Inherited characteristics caused by genes situated on sex chromosomes, most commonly represented by X-linked recessive disorders such as hemophilia A and red-green color blindness.