Embryology & Reproductive Physiology – Key Vocabulary

Vocabulary flashcards covering embryology from fertilization through gastrulation, germ layers, placenta, gametogenesis, fertilization mechanics, neural tube defects, and pharyngeal arch derivatives.

Pre-Embryonic Stage

First two weeks after fertilization; conceptus is undergoing cleavage and implantation.

Amniotic Cavity

forms above the epiblast during formation of bilaminar disk

Embryonic Stage

Weeks 3-8 of development when the basic body plan and organ primordia form.

Fetal Stage

Weeks 9-birth; period of growth and functional maturation of organs.

Fertilization Site

Ampulla of the fallopian tube where sperm and secondary oocyte unite.

Conceptus

The fertilized egg and all its derivatives at any stage of prenatal development.

Cleavage

Rapid mitotic divisions of the zygote without overall growth in size, producing blastomeres.

Blastomere

Individual cell produced during cleavage of the zygote.

Morula

Solid ball of ~16 totipotent cells that enters the uterus ~3 days post-fertilization.

outer cells become trophoblasts, inner cells become embryoblasts

Totipotent Cell

Cell capable of forming all embryonic and extra-embryonic tissues.

Blastocyst

Hollow, ~100-cell stage consisting of trophoblast, embryoblast, and blastocoel.

Embryoblast

Inner cell mass of the blastocyst; pluripotent cells that form the embryo proper.

Trophoblast

Outer blastocyst layer that forms chorion and contributes to placenta

Divides into cytotrophoblasts and syncytiotrophoblasts

Implantation

Attachment and penetration of the blastocyst into the endometrium at week 1

Uses enzymes secreted by trophoblast

Syncytiotrophoblast

Invasive, multinucleated trophoblast layer that erodes endometrium and secretes hCG

Form villi that reach into maternal tissue

hCG (Human Chorionic Gonadotropin)

Hormone from syncytiotrophoblast that maintains maternal corpus luteum to secrete progesterone.

Corpus Luteum

Ovarian structure producing progesterone to sustain early pregnancy.

Progesterone

maintains endometrium, stimulated decidual cell growth for nutrients

Bilaminar Disc

Two-layered embryonic structure (epiblast + hypoblast) formed during week 2.

Epiblast

Dorsal layer of bilaminar disc that gives rise to amnion

Hypoblast

Ventral layer of bilaminar disc that helps form yolk sac lining.

Yolk Sac

Early membrane providing nutrients, gas exchange, and first blood formation.

Amnion

Membrane that encloses the embryo in fluid, cushioning and permitting movement.

Primitive Streak

Midline groove on epiblast that establishes body axes and initiates gastrulation.

Gastrulation

Process converting bilaminar disc into trilaminar disc (ectoderm, mesoderm, endoderm).

Ectoderm

Outer germ layer forming skin and nervous system.

Mesoderm

Middle germ layer forming muscular, urogenital, and cardiovascular system.

Endoderm

Inner germ layer forming digestive and respiratory lining and associated organs.

Allantois

Embryonic membrane arising from yolk sac; contributes to umbilical cord and bladder.

Chorion

Membrane derived from trophoblast; fetal component of the placenta.

Seminiferous Tubule

Highly coiled testicular tubule where spermatogenesis occurs.

Testes

Located in scrotum

Produce sperm and testosterone

Leydig Cell

Cells on the outside of seminiferous tubules secreting testosterone.

Sertoli Cell

Supporting cell inside seminiferous tubule that nurtures developing sperm.

Separated by tight junctions

Tight Junctions

basal compartment closer to base, lumenal compartment towards the lumen

allow chemical isolation for different stages of spermatogenesis

Spermatogonium

Diploid stem cell that begins spermatogenesis via mitosis.

Mitosis results in one spermatogonium and one primary spermatocyte

Primary Spermatocyte

Diploid cell entering undergoes meiosis I to form two secondary spermatocytes.

Secondary Spermatocyte

Haploid cell undergoing meiosis II to yield 4 spermatids.

Spermatid

Immature haploid germ cell that differentiates into spermatozoon via spermiogenesis

Spermiogenesis

Transformation of spermatids into motile spermatozoa.

Basal Compartment

Region between Sertoli cells housing spermatogonia; isolated by tight junctions.

Lumenal Compartment

Adluminal region where primary spermatocytes complete meiosis and spermatids mature.

Peristalsis (in Testes)

Muscular contractions that push sperm from tubules to epididymis.

Epididymis

Tubular organ where sperm mature and are stored until ejaculation.

Egg Maturation

Eggs created during fetal development

One egg matures each month after puberty

Mature egg is released during ovulation

Oogonium

Diploid female germ cell formed during fetal life, multiply by mitosis.

Hormone Secreted by Ovary

estrogen, progesterone, inhibin

Primary Oocyte

Result from oogonium development

Diploid oocyte arrested in prophase I from birth until puberty.

Secondary Oocyte

Haploid oocyte receiving majority of cytoplasm, released at ovulation, arrested in metaphase II until fertilization

Resumption of Meiosis

some primary oocytes resume Meiosis I at puberty

Polar Body

Small, non-functional cell produced during unequal meiotic divisions of oogenesis.

Ovum

Mature egg cell formed after completion of meiosis II at fertilization.

Ovulation

Release of a secondary oocyte from the ovarian follicle.

Sperm Head

nucleus with DNA, acrosome

Acrosome

enzyme filled “warhead” to penetrate egg’s outer layer

Sperm Middle Section

contains large mitochondria wrapped around flagellar base

Sperm Tail

flagella, propeller for motility

Steps of Fertilization

sperm binding to zona pellucida

acrosomal reaction

membrane binding

cortical reaction

fusion

Sperm Binding

sperm binds to glycoproteins in zona pellucida

Membrane Binding (Fertilization)

sperm and egg plasma membranes fuse

initiates cortical reaction

Acrosomal Reaction

Enzyme release from sperm acrosome to digest zona pellucida.

Cortical Reaction

Exocytosis of egg cortical granules that block polyspermy

alter zona pellucida by destroying sperm binding glycoproteins

Polyspermy

Fertilization of an egg by multiple sperm, prevented by cortical reaction.

Zona Pellucida

Glycoprotein shell around oocyte and early embryo; mediates sperm binding.

Mitochondrial DNA Inheritance

Transmission of mitochondria almost exclusively from the mother via the egg.

Placenta

Temporary organ of exchange between mother and fetus composed of chorion and decidua.

Primary organ for nutrient and gas exchange, waste removal, and hormone production to sustain pregnancy

Umbilical Cord

Fetal connection to placenta containing two arteries and one vein within Wharton’s jelly.

Umbilical Arteries

2, low in oxygen

Umbilical Veins

1, high in oxygen, carries blood from placenta to fetus

Uterine Arteries

bring oxygen rich blood into placenta, blood released into maternal pool

Uterine Veins

drain blood away from maternal pool

Chorionic Plate

Fetal surface of placenta containing branching villi, trophoblasts, and fetal vessels.

Basal Plate

Maternal side of placenta where uterine arteries and veins open into intervillous space.

Intervillous Space

Maternal blood pool bathing chorionic villi for diffusion exchange.

Chorionic Villi

Finger-like fetal projections containing capillaries that invade maternal blood pools.

Blastocyst Hatching

Loss of zona pellucida allowing trophoblast contact with endometrium.

Cytotrophoblast

Inner layer of trophoblast maintaining individual cell boundaries inside villi.

Line the villi

Apposition

valleys/crypts form in proliferated endometrium, blastocyst settles in a valley

Adhesion

trophoblasts invade endometrial tissue, leads to a firm connection

Fetal Blood Vessels

formed inside the villi, come close to maternal blood pool, separated by trophoblast membranes

allow for exchange of nutrients and oxygen, and diffusion out of waste and carbon dioxide

Notochord

Mesodermal rod that induces neural plate formation via ectoderm thickening.

Neural Tube

Arises from folding of the neural plate

Ectodermal structure forming brain and spinal cord after neurulation.

Neural Crest Cells

Migratory ectodermal cells giving rise to peripheral nerves, melanocytes, etc.

Endoderm Derivatives

GI tract, liver, pancreas, lungs, bladder lining

Mesoderm Derivatives

muscles, bones, skeleton, dermis, kidneys, bladder, overies/testes

Ectoderm Derivatives

epidermis, hair, nails, sweat glands, CNS, PNS

Spina Bifida

Neural tube defect characterized by incomplete closure of spinal column

Results in an opening in the vertebrae

Spina Bifida Occulta

Mild form with small vertebral gap

Often asymptomatic, may have dimple/birthmark/tuft of hair

Meningocele

Spina bifida cystica variant with protrusion of meninges but not spinal cord.

Mild symptoms

Myelomeningocele

Severe spina bifida cystica with protrusion of meninges and spinal cord

Paralysis, bladder and bowel dysfunction

Hydrocephalus

accumulation of fluid in the brain

associated with myelomeningocele

Chairi Malformation Type II

brainstem and cerebellum drop below normal level

associated with myelomeningocele

Causes & Risks for Spina Bifida

folic acid deficiency, previous child with NTD, diabetes, obesity, certain medications

Diagnosis of Spina Bifida

detection of AFP via blood draw or amniocentesis, ultrasound most accurate

Pharyngeal Arch

Embryonic bulge in head region containing cartilage, artery, and cranial nerve.

Meckel’s Cartilage

Cartilage of first pharyngeal arch forming malleus, incus, and mandible template.

Reichert’s Cartilage

Cartilage of second arch forming stapes, styloid process, lesser hyoid horn.

Cervical Sinus

Temporary depression formed as second arch overgrows grooves 2-4; normally obliterates.

First Pharyngeal Groove & Pouch

external auditory meatus, tympanic cavity, eustachian tube, tympanic membrane

Second Pharyngeal Pouch

tonsillar fossa after palatine tonsil development