Chapter 3 Embryology

Amniocentesis

prenatal diagnostic procedure that samples amniotic fluid

Amniotic Cavity

fluid-filled cavity facing the epiblast layer

Appositional Growth

growth by layering outside of a tissue mass, such as cartilage, bone, enamel, dentin, or cementum

Bilaminar Embryonic Disc

circular plate of bilayered cells from the blastocyst

Bilateral Symmetry

each half of the embryo mirrors the other half

Blastocyst

structure consisting of trophoblast cells and an inner mass of cells that forms the embryo

Caudal End

tail end of a structure

Cephalic End

head end of a structure

Cleavage

mitosis that converts the zygote into a blastocyst

Cloacal Membrane

membrane at the caudal end of the embryo that will become the future anus

Cytodifferentiation

development of different cell types

Developmental Disturbance

a congenital malformation or anomaly

Differentiation

change in embryonic cells so they become structurally and functionally distinct

Ectoderm

layer of the trilaminar embryonic disc derived from the epiblast layer and lining the stomodeum

Embryo

structure derived from the implanted blastocyst

Embryoblast Layer

small inner mass of embryonic cells in the blastocyst

Embryonic Cell Layers

germ layers derived from an increased number of embryonic cells

Embryonic Folding

folding of the embryo that places tissues into their correct positions

Embryonic Period

prenatal developmental period of the embryo from the 2nd to the 8th week

Embryology

study of prenatal development

Endoderm

layer of the trilaminar embryonic disc derived from the hypoblast layer

Epiblast Layer

superior layer in the bilaminar disc

Fertilization

process in which sperm penetrates the ovum

Fetal Period

prenatal developmental period of the fetus from the 3rd to the 9th month

Foregut

anterior part of the future digestive tract, or primitive pharynx, that forms the oropharynx

Fusion

joining of embryonic tissue from two separate surfaces that eliminates the furrow between adjacent swellings; can also refer to a developmental disturbance in which adjacent tooth germs unite to form a large tooth

Hindgut

posterior part of the future digestive tract

Histodifferentiation

development of different tissue types

Hypoblast Layer

inferior layer in the bilaminar disc

Implantation

embedding of the blastocyst in the endometrium

Induction

action of one group of cells on another that leads to a developmental pathway in the responding tissue

Interstitial Growth

growth from deep within a tissue or organ

Invagination

cavity or pouch formation by turning inside out or folding back

Karyotype

the number and appearance of chromosomes in a cell, including their size, shape, and arrangement

Maturation

attainment of adult size as well as adult form and function

Meiosis

process of reproductive cell production that ensures the correct number of chromosomes

Mesenchyme

embryonic connective tissue

Mesoderm

embryonic layer located between the ectoderm and endoderm

Midgut

middle part of the future digestive tract

Mitosis

cell division occurring in phases that results in two daughter cells

Morphodifferentiation

development of differing forms to create specific structures

Morphogenesis

process of development of specific tissue morphology

Morphology

form or shape of a structure

Neural Crest Cells

specialized group of cells that develop from neuroectoderm, migrate from the crests of the neural folds, and disperse within the mesenchyme

Neural Folds

raised edges of the neural plate surrounding the deepening neural groove

Neural Groove

groove formed by the further growth and widening of the neural plate

Neural Plate

centralized band of cells extending the length of the embryo

Neural Tube

tube formed when the neural folds meet and fuse superior to the neural groove

Neuroectoderm

specialized group of cells differentiating from ectoderm

Oropharyngeal Membrane

membrane at the cephalic end of the embryo

Ovum

female reproductive cell, or egg, that can be fertilized

Placenta

temporary prenatal organ that supports the developing embryo

Preimplantation Period

time before implantation

Prenatal Development

processes occurring from the beginning of pregnancy to birth

Primitive Streak

furrowed, rod-shaped thickening in the midline of the embryonic disc

Primordium

earliest recognizable structure during the development of an organ or tissue during prenatal development

Proliferation

controlled cellular growth

Sperm

cell containing the male contribution of chromosomal information that fertilizes the female ovum

Somites

paired cuboidal aggregates of cells differentiated from mesoderm

Tetracycline Stain

intrinsic tooth stain caused by the antibiotic tetracycline when used during tooth development

Teratogens

environmental agents or factors that cause developmental disturbances

Trilaminar Embryonic Disc

embryonic disc with three layers: ectoderm, mesoderm, and endoderm

Trophoblast Layer

layer of peripheral cells of the blastocyst

Yolk Sac

fluid-filled cavity facing the hypoblast layer

Zygote

fertilized egg formed from the union of an ovum and sperm