Week 2 (1/20) Embryonic Development

Exam 1

stages of pre-embryonic development

cleavage, blastocyst stage, impantation, and gastrulation

cleavage stage

period of rapid mitotic cell division, producing blastomeres about 1 day after fertilization

fertilization

fusion of sperm and egg to create a zygote

blastocyst stage

hollow ball that forms when the morula contains exactly 32 cells. cell divisions continue and these cells start to specialize

implantation stage

blastocyst adheres to the endometrium of the uterine wall. trophoblasts specialize into cellular and syncytial subtypes. the bilaminar embryonic disc forms.

gastrulation stage

formation of the primary germ layers begins, from which all tissues eventually differentiate. the embryonic disc elongates and the primitive streak appears. the bilaminar disc becomes an embryonic disc

blastomere

an identical cell created by rapid cleavage stage divisions

morula

solid mass of blastomeres surrounded by a zona pellucida

zona pellucida

protective glycoprotein sheath of the morula

blastocyst

fluid-filled ball that forms when the morula contains exactly 32 cells. divided into the outer trophoblast layer and the clustered embryoblast region

trophoblast

contains a fluid cavity that will eventually become part of the placenta. it secretes enzymes to break down the zona pellucida and uterine wall

embryoblast

will eventually become the bilaminar embryonic disc and embryo

bilaminar embryonic disc

originates from the inner cell mass. the deeper layer is the hypoblast and the superficial layer the epiblast.

epiblast

superficial layer of the bilaminar embryonic disc that forms the amniotic membrane and allows the new embryo to move

cellular trophoblast

the inner layer of the trophoblast cells

syncytial trophoblast

the outer layer of trophoblast cells

hCG (human chorionic gondotropin)

hormone that protects the corpus leutum by prompting continued production of estrogen and progesterone so menustration can’t happen

primary germ layers

endoderm, ectoderm, and mesoderm in the new trilaminar embryonic disc

endoderm

germ layer that develops into lung/alveolar cells, thyroid cells, and digestive/pancreatic cells

ectoderm

germ layer that develops into skin cells of the epidermis, neurons, and pigment cells

mesoderm

germ layer that organizes into the notochord and mesenchyme, the origin of all connective tissue

4 extraembryonic membranes

amnion, yolk sac, allantois, and chorion

amnion

extraembryonic membrane that develops from the epiblast and forms the amniotic cavity, preventing new limbs from adhering to each other

yolk sac

extraembryonic membrane that forms from primitive gut cells and hangs from ventral surface of the embryo. eventually forms gut cells and origin of early blood cells

allantois

extraembryonic membrane that forms from pocket of cells in yolk sac, becomes the structural base for the umbilical cord

chorion

extraembryonic membrane that helps form the placenta, enclosing the embryonic body and all other membranes