Embryology Lecture Vocabulary

Vocabulary flashcards covering key terms from fertilisation, cleavage, gastrulation, neurulation, and stem‐cell biology in the Embryology lecture.

Embryology

The scientific study of embryonic development from fertilisation through organogenesis.

Fertilisation

Fusion of haploid sperm and egg to form a diploid zygote; involves contact, acrosomal, and cortical reactions.

Zygote

The first diploid cell formed after fertilisation.

Cleavage

Rapid mitotic divisions that partition the zygote into many smaller blastomeres.

Blastomere

An individual cell produced during cleavage.

Blastula (Blastocyst in mammals)

Hollow ball of blastomeres surrounding a fluid-filled cavity (blastocoel).

Blastocoel

The fluid-filled cavity inside a blastula.

Gastrulation

Cell rearrangement that forms the three embryonic germ layers and produces a gastrula.

Germ layers

Ectoderm, mesoderm, and endoderm formed during gastrulation.

Organogenesis

Formation of rudimentary organs from the germ layers.

Neurulation

Early organogenesis event that forms the neural tube from ectoderm.

Acrosomal reaction

Release of enzymes from the sperm acrosome that digests the egg’s jelly coat and enables species-specific binding.

Acrosome

Enzyme-filled vesicle at the tip of a sperm that initiates the acrosomal reaction.

Cortical reaction

Exocytosis of cortical granules in the egg leading to a fertilisation envelope that blocks polyspermy (slow block).

Fast block to polyspermy

Rapid depolarisation of the egg membrane due to Na⁺ influx that prevents additional sperm fusion.

Polyspermy

Penetration of an egg by more than one sperm; lethal for the embryo.

Holoblastic cleavage

Complete division of the egg; occurs in mammals, amphibians, and echinoderms.

Meroblastic cleavage

Partial division restricted to the animal pole due to abundant yolk; typical of birds, reptiles, fish, insects, and monotremes.

Vegetal pole

Yolk-rich end of an egg where cleavage is slowed or impeded.

Animal pole

Yolk-poor end of an egg where cleavage is most active.

Cleavage furrow

Indentation that partitions cells during cleavage divisions.

Blastodisc

Small disc of cytoplasm at the animal pole of bird and reptile eggs where cleavage occurs.

Blastoderm

Multicellular layer formed from the blastodisc in meroblastic embryos.

Inner cell mass (ICM)

Cluster of cells inside a mammalian blastocyst that forms the embryo and provides pluripotent stem cells.

Trophoblast

Outer layer of mammalian blastocyst that forms the chorion and contributes to the placenta.

Primitive streak

Longitudinal thickening in the epiblast of amniote embryos marking the site of cell ingress during gastrulation.

Epiblast

Upper layer of the blastoderm/ICM that gives rise to the embryo proper.

Hypoblast

Lower layer beneath the epiblast that contributes to extra-embryonic endoderm.

Blastopore

Opening in frog gastrulation where cells invaginate; later becomes the anus.

Archenteron

The embryonic gut cavity formed during gastrulation.

Notochord

Rod-like structure derived from dorsal mesoderm that signals neural development and forms the core of vertebral column.

Neural plate

Thickened ectoderm above the notochord that folds to form the neural tube.

Neural tube

Ectodermal tube that develops into the brain and spinal cord.

Neural crest cells

Migratory cells from neural fold edges that form neurons, pigment cells, bone, and other tissues.

Somites

Segmented blocks of paraxial mesoderm flanking the neural tube that form vertebrae, ribs, and associated muscles.

Fate map

Diagram showing which regions of an early embryo give rise to specific tissues and organs.

Tinman gene

Drosophila gene that positions the heart; vertebrate homologues perform similar cardiac functions.

Totipotent cell

Cell capable of forming all embryonic and extra-embryonic (placental) tissues; e.g., 1- to 8-cell blastomeres.

Pluripotent cell

Cell that can form all body cell types but not extra-embryonic tissues; e.g., inner cell mass cells or ESCs.

Multipotent cell

Adult stem cell with limited differentiation potential (e.g., mesenchymal stem cells).

Embryonic stem cells (ESCs)

Pluripotent cells isolated from the inner cell mass of early embryos.

Induced pluripotent stem cells (iPSCs)

Somatic cells reprogrammed to a pluripotent state through gene manipulation.

Primitive endoderm

Layer derived from the ICM that contributes to the yolk sac; expresses factors such as Gata6 and Sox17.

Mesendoderm

Embryonic region that gives rise to both mesoderm and endoderm lineages.

Fertilisation envelope

Hardened vitelline layer formed after the cortical reaction that provides the slow block to polyspermy.