Veterinary Embryology and Placentation Flashcards

Flashcards covering key embryological processes, germ layer derivations, neurulation anomalies, body folding, and comparative mammalian placentation.

Corona Radiata

The structure consisting of the zona pellucida surrounding the oocyte along with its surrounding layers of follicular cells.

Capacitation

The essential physiological maturation process that sperm must undergo within the female reproductive tract before gaining the capability to fertilize an oocyte.

Spermatozoon Anatomy

A mature sperm cell consisting of a head covered by an acrosome cap, a neck, a middle piece containing a mitochondrial sheath, and a tail.

Zona Reaction

The structural and chemical change in the zona pellucida triggered when a sperm enters the oocyte, rendering the zona impenetrable to additional sperm and preventing polyspermy.

Male Pronucleus

The nuclear structure that forms inside the fertilized oocyte from the enlarged nucleus of the penetrating sperm head.

Female Pronucleus

The nucleus formed within the oocyte once it completes its second meiotic division following sperm penetration.

Blastomere

An individual embryonic cell formed during the early cleavage divisions of a zygote.

Morula

A solid embryonic stage consisting of roughly 8 to 16 blastomeres arranged into a central cell core and a superficial outer layer created by compaction.

Trophoblast

The external cell layer of the morula and blastocyst that forms tight junctions to protect the embryoblast and gives rise to fetal placental membranes.

Embryoblast

The inner cell mass of the blastocyst that gives rise to the body of the embryo.

Rauber's Layer

The portion of trophoblast cells directly overlying the embryoblast in domestic mammals, which disintegrates during early development.

Blastocystic Cavity

The fluid-filled internal space created by blastomere secretions that separates the embryoblast from the trophoblast in a blastocyst.

Exocoelomic Cavity

The name assigned to the blastocystic cavity at the stage when hypoblast cells begin migrating along the ventral surface of the embryoblast.

Primitive Yolk Sac

The embryonic cavity formed when hypoblast cells extend fully to line the inner surface of the exocoelomic cavity.

Epiblast

The dorsal columnar cell layer of the bilaminar embryonic disc that replaces Rauber's layer and gives rise to all three primary germ layers.

Hypoblast

The ventral cuboidal cell layer of the bilaminar embryonic disc that migrates to line the exocoelomic cavity and form the primitive yolk sac.

Prechordal Plate

A localized circular thickening of columnar hypoblast cells at the cranial end of the embryonic disc that marks the future site of the mouth.

Primitive Streak

A linear midline band appearing on the dorsal epiblast surface from caudal to cranial that marks the commencement of gastrulation.

Primitive Node

An elevated organizer region at the cranial end of the primitive streak that establishes the body axes of the embryo.

Gastrulation

The process of cell migration from the epiblast through the primitive streak that transforms the bilaminar disc into a trilaminar embryonic disc.

Notochord

A midline cellular axis ventral to the ectoderm that provides structural rigidity, marks future vertebral body locations, and induces neurulation.

Neurulation

The formation of the neural tube through invagination of the neural plate to form a neural groove flanked by neural folds that subsequently fuse.

Anencephaly

A severe congenital anomaly resulting from failure of the rostral neuropore to close during neurulation, leading to partial absence of the brain.

Spina Bifida

A neural tube defect caused by incomplete closure of the caudal neuropore and failure of the vertebral neural arches to fuse.

Neural Crest Cells

A population of migratory cells detached from the neural fold borders that form spinal, autonomic, and cranial ganglia, melanocytes, and facial skeleton structures.

Paraxial Mesoderm

The thick mesodermal columns situated adjacent to the neural tube and notochord that segment into somites.

Somites

Segmented blocks of paraxial mesoderm that give rise to the sclerotome, myotome, and dermatome.

Sclerotome

The ventromedial section of a somite that forms the vertebrae, ribs, axial skeleton, and parts of the neurocranium.

Myotome

The subunit of a somite that gives rise to all voluntary skeletal muscle of the head, trunk, and limbs.

Dermatome

The dorsal subunit of a somite that forms the dermis of the skin over dorsal body regions.

Intermediate Mesoderm

The longitudinal strip of mesoderm lying between paraxial and lateral plate mesoderm that forms the gonads and urogenital system.

Lateral Plate Mesoderm

The unsegmented lateral region of mesoderm that splits into a parietal (somatic) layer and a visceral (splanchnic) layer.

Choriovitelline Membrane

The initial temporary placenta formed by the apposition and vascularization of the yolk sac extraembryonic mesoderm with the chorion.

Chorioallantoic Membrane

The definitive placental membrane formed by the fusion of the vascularized allantois with the chorion.

Epitheliochorial Placenta

A placenta classification present in horses and pigs in which all six maternal and fetal tissue layers remain intact and apposed.

Synepitheliochorial Placenta

A placenta classification present in ruminants characterized by an attenuated combined cryptal layer of maternal and fetal epithelium containing fetal binucleate cells.

Endotheliochorial Placenta

A placenta classification present in dogs and cats where maternal uterine epithelium and connective tissue are eroded, putting fetal chorionic epithelium in direct contact with maternal blood vessel endothelium.

Haemochorial Placenta

A placenta classification present in humans where maternal uterine tissue and capillary walls are completely eroded, leaving fetal chorionic villi bathed directly in maternal blood.

Endometrial Cups

Specialized transient structures in equine placentation, derived from the chorionic girdle, that invade the maternal endometrium to secrete equine chorionic gonadotropin.

Placentome

The functional unit of ruminant placentation consisting of a maternal caruncle united with a fetal cotyledon.

Monozygotic Twins

Twins resulting from the division of a single fertilized ovum (zygote).

Dizygotic Twins

Twins resulting from two separate ova released during the same estrous cycle and fertilized by two distinct sperm cells.