VETS1060 Embryology – Vocabulary Flashcards

Vocabulary flashcards summarising key terms and definitions from the VETS1060 Embryology lecture on fertilisation, cleavage, gastrulation, and organogenesis.

Embryology

The study of embryonic development from fertilisation to organ formation.

Four stages of embryonic development

Fertilisation, cleavage, gastrulation, and organogenesis (including neurulation).

Fertilisation

Fusion of haploid sperm and egg to produce a diploid zygote.

Zygote

The single-celled, diploid product of fertilisation.

Cleavage

Rapid mitotic divisions that partition the zygote into smaller cells called blastomeres.

Blastomere

An individual cell produced during cleavage divisions.

Blastula / Blastocyst

Hollow ball of cells (blastula; blastocyst in mammals) formed after cleavage.

Blastocoel

Fluid-filled cavity inside the blastula/blastocyst.

Gastrulation

Reorganisation of the blastula into a three-layered gastrula.

Gastrula

Embryo after gastrulation containing ectoderm, mesoderm, and endoderm.

Embryonic germ layers

Ectoderm, mesoderm, and endoderm produced during gastrulation.

Ectoderm

Outer germ layer; forms epidermis, nervous system, hair, and oral/nasal lining.

Mesoderm

Middle germ layer; forms muscle, skeleton, circulatory system, kidneys, and more.

Endoderm

Inner germ layer; forms gut lining, liver, pancreas, and respiratory tract.

Organogenesis

Process by which specific organs develop from germ layers.

Neurulation

Early organogenic event forming the neural tube from ectoderm.

Tinman gene

Drosophila gene controlling heart position; homologues direct vertebrate heart development.

Acrosomal reaction

Release of enzymes from sperm acrosome that digest egg jelly coat and allow binding.

Cortical reaction

Exocytosis of cortical granules in egg that hardens vitelline layer, creating fertilisation envelope and blocking polyspermy.

Polyspermy

Entry of more than one sperm into an egg; prevented by fast and slow blocks.

Fast block to polyspermy

Rapid Na⁺-induced depolarisation of egg membrane immediately after sperm fusion.

Slow block to polyspermy

Cortical reaction that forms a long-lasting fertilisation envelope.

Cortical granules

Egg vesicles whose enzymes modify vitelline layer during slow block.

Vitelline layer

Outer egg membrane that hardens into the fertilisation envelope after cortical reaction.

Fertilisation envelope

Hardened vitelline layer that prevents additional sperm entry.

Holoblastic cleavage

Complete cleavage through the entire egg (mammals, amphibians, echinoderms).

Vegetal pole

Egg end rich in yolk; cleavage furrows slow here.

Animal pole

Egg end with less yolk; cleavage is more rapid here.

Meroblastic cleavage

Partial cleavage confined to yolk-poor cytoplasm (birds, reptiles, fish, insects, monotremes).

Blastodisc

Small disc of dividing cells at animal pole of meroblastic eggs.

Blastoderm

Multicellular sheet formed from blastodisc divisions in meroblastic embryos.

Inner cell mass (embryoblast)

Group of cells inside mammalian blastocyst that forms the embryo and yields embryonic stem cells.

Trophoblast

Outer blastocyst layer forming chorion and later placenta, not embryo proper.

Primitive streak

Longitudinal thickening in epiblast where gastrulation cell movements occur in birds and mammals.

Archenteron

New digestive tract cavity formed during gastrulation, replacing the blastocoel.

Blastopore

Invaginated opening on gastrula surface where cells migrate inward; becomes anus in frogs.

Epiblast

Upper layer of inner cell mass that gives rise to the embryo proper.

Hypoblast

Lower layer of inner cell mass contributing to extraembryonic tissues.

Totipotent stem cells

Cells (e.g., 8-cell stage blastomeres) capable of forming all embryonic and extraembryonic tissues.

Pluripotent stem cells

Cells (e.g., inner cell mass, ESCs) that can form all body cell types but not extraembryonic tissues.

Multipotent stem cells

Adult stem cells (e.g., mesenchymal stem cells) with limited, tissue-specific differentiation.

Induced pluripotent stem cells (iPSCs)

Pluripotent cells created by reprogramming differentiated adult cells.

Neural plate

Ectodermal region above notochord that folds to form neural tube.

Notochord

Rod-like mesoderm structure that signals neural plate formation and patterns embryo.

Neural tube

Embryonic structure that becomes brain and spinal cord.

Neural crest cells

Migratory cells from neural folds that form neurons, pigment cells, bone, and more.

Somites

Segmented mesoderm blocks that produce vertebrae, ribs, and associated muscles.