HSCI 2020 Final: Human Development

Polyploidy

a condition where a cell has more than two complete sets of chromosomes

Aneuploidy

an abnormal number of chromosomes (45/47 instead of 46)

trisomy

a form of aneuploidy where a chromosome is present in triplicate (3 copies instead of 2), like trisomy 21

down syndrome

caused by trisomy 21, characterized by intellectual disability and physical features

turner syndrome

a condition in females with only one X chromosome (45, X), leading to being short and infertile

Klinefelter syndrome

genetic condition in males with an extra X chromosome (47, XXY), often causes infertility, and some female secondary traits

zygote

a single-cell formed by the fusion of sperm and egg

fertilization

the fusion of male and female gametes to form a zygote

cleavage

rapid mitotic divisions of the zygote without growth, forming smaller cells (blastomeres)

two-cell stage

a zygote that has divided into two blastomeres

four-cell stage

the next cleavage stage, where the zygote has divided into four cells

morula

a solid ball of 16-32 cells (blastomeres) resulting from cleavage, usually by day 3

zone pellucida

a glycoprotein shell that surrounds the zygote and early embryo, prevents premature implantation

blastocyt

a hollow ball of cells that are formed around day 5, ready for implantation

trophoblast

the outer layer of cells in the blastocyst, contributes to the placenta

inner cell mass

a group of cells in the blastocyst that will become the embryo

blastocoele

the fluid-filled cavity within the blastocyst

hypoblast

a layer of cells in the bilaminar embryo that contributes to the yolk sac

epiblast

The upper layer of the bilaminar embryo that gives rise to all three germ layers

syncytiotrophoblast

a multinucleated outer layer of the trophoblast that invades the endometrium and secretes hCG

ectoderm

the outer germ layer that forms skin, nervous system, and sensory organs

endoderm

the inner germ layer that forms the digestive and respiratory tracts

mesoderm

the middler germ layer that forms muscles, bones, heart, blood, and reproductive organs

gastrula

the stage after the blastocyst when the three germ layers form

gastrulation

the process during which the three germ layers are formed from the epiblast

yolk sac

early site of blood formation and nutrient transfer; made from endoderm and mesoderm

amnion

a membrane that forms the amniotic sac, which protects the embryo in fluid

allantois

involved in early fluid exchange and later contributes to umbilical cord and bladder development

chorionic villi

fingerlike projections of the chorion that invade the maternal tissue and help form the placenta

umbilicus

the navel; makes where umbilical cord was attached

hCG

hormones produced by the syncytiotrophoblast; maintains the corpus lutem

hPL

a hormone that modifies maternal metabolism to support fetal growth

relaxin

a hormone that loosens pelvic ligaments, and softens cervix for birth

embryo

the developing organism from fertilization to 8 weeks

fetus

the developing organism from 9 weeks to birth