Chapter 47: Animal Development

Term DefinitionModel organisms used to study development; chosen for the ease

with which they can be studied in the laboratory Fertilization formation of a diploid zygote from a haploid egg

and a haploid spermAcrosomal reaction triggered when the sperm comes in contact with

the eggAcrosome releases hydrolytic enzymes that digest material

surrounding the egg Fast block to polyspermy sperm-egg fusion and depolarization of egg

membraneCortical reaction initiates fusion of egg and spermSlow block to polyspermy formation of fertilization envelopeCapacitation secretions in the mammalian female reproductive

tract alter sperm motility and structure; must occur before sperm are able to fertilize an egg

Zona pellucida extracellular matrix of the eggNo fast block to polyspermy identified in mammals Hyaluronidase enzyme released by spermZP3 from the zona pellucid; a glycopreotein that serve

as a sperm receptorCleavage follows fertilization; a period of rapid cell division

without growthBlastomeres smaller cells formed from partitioning of cleavage

of the cytoplasm of one large cellBlastula a ball of cells with a fluid-filled cavity (blastocoel)Yolk stored nutrientsVegetal pole has more yolkAnimal pole has less yolkHoloblastic cleavage complete division of the egg; occurs in species

whose eggs have little or moderate amounts of yolk

Meroblastic cleavage incomplete division of the egg; occurs in species with yolk-rich eggs

Morphogenesis Process by which cells occupy their appropriate locations

Gastrulation Movement of cells from the blastula surface to the interior of the embryo; rearranges the cells of a blastula into a three-layered embryo (gastrula)

Organogenesis Formation of organsEmbryonic layers Three layers produced by gastrulationEctoderm Forms the outer layerEndoderm Lines the digestive tractMesoderm Partly fills the space between the endoderm and

ectodermArchenteron Newly formed cavityBlastopore Where archenteron opens to; becomes the anusDorsal lip Part above the crease along the region where the

gray crescent formed© Sio 2014

Epiblast Upper layer of the embryo formed prior gastrulation

Hypoblast Lower layer of the embryo formed prior gastrulation

Primitive streak The midline when thickenedBlastocyst Human equivalent of the blastulaInner cell mass Cluster of cells at one end of the blastocystTrophoblast Outer epithelial layer of the blastocyst; does not

contribute to the embryo; initiates implantationExtraembryonic membrane Formed after expansion of trophoblast after

implantationMonotremes Egg-laying mammalsAmnion Sac of fluid surrounding the embryo; protects

embryo from dessication and allows reproduction on dry land; encloses the amniotic fluid

Amniotes Reptiles, mammals, birdsChorion Functions in gas exchangeYolk sac Encloses the yolkAllantois Disposes of waste products and contributes to gas

exchangeOrganogenesis Various regions of the embryonic layers develop

into rudimentary organsNotochord Forms from mesoderm early in vertebrate

organogenesisNeural plate Forms from neural ectoderm early in vertebrate

organogenesisNeural tube Forms when neural plate curves inward; will

become the central nervous systemNeural crest cells Develop along the neural tube of vertebrates and

form various parts of the embryoSomites Blocks formed from mesoderm lateral to the

notochordCoelom Body cavity; formed from splitting of mesoderm

lateral to somites

© Sio 2014