BIOL 80A Final | Fertilization & Embryogenesis

what is fertilization?

the process in which gametes (an egg and sperm) fuse to form a zygote

what is a zygote?

the diploid cell formed from the union of sperm and egg, containing a complete set of chromosomes for a new organism

what is the zona pellucida?

a protective layer surounding the mammalian egg that sperm must penetrate to reach the egg’s plasma membrane

what is an acrosome (acrosomal reaction)?

the sperms’ cap containing digestive enzymes that break down the zona pellucida, allowing sperm entry (the reaction).

why is it crucial only one sperm fertilizes an egg?

to ensure the resulting zygote receives only one complete diploid set of chromosomes, preventing genetic abnormalities

what is a polysperm block (prevention of multiple sperm)?

proteins released by the egg after the first sperm entry that modify the egg surface to block other sperm from fusing

what happens to the nuclei during fertilization?

the nuclear membranes of the sperm and egg break down, and their haploid nuclei fuse to form a single diploid nucleus

embryogenesis begins with what single-celled structure?

a zygote

what is the process of rapid cell division events following fertilization?

cleavage

what stage is formed by cleavage (~100 cells) and is a spherical layer of cells surrounding a fluid-filled cavity?

the blastula

what is the fluid-filled cavity within the blastula called?

the blastocoel

in the transition from blastula to blastocyst, cells arrange into what two layers?

the inner cell mass (embryoblast) and an outer layer called the trophoblast

which part of the blastocyst forms the actual embryo?

tbe inner cell mass (aka embryoblast)

what types of cells make up the inner cell mass at the blastocyst stage?

embryonic stem cells (which are pluripotent)

what is the function of the trophoblast layer?

it contributes to the placenta and nourishes the embryo

when does the blastocyst stage typically occur and near what event?

~5 days after fertilization, near the time of implantation in the uterus

where does fertilization typically occur?

as the egg is traveling through the fallopian tube

what is the next stage after the blastocyst, where cells spatially rearrange and fold?

gastrulation

what structure is formed as a result of gastrulation?

the gastrula

what are the three layers of cells formed during gastrulation called?

germ layers

when does the gastrula stage typically occur in human development?

14-21 days after fertilization (week 3)

what are the three specific germ layers?

the endoderm, the ectoderm, and the mesoderm

what is the potential of the stem cells within the three germ layers?

they are pluripotent and will give rise to all of the specialized cells/tissues of the body

what is organogenesis?

the process where organs form from the germ layers

what happens during organogenesis?

organs form from the germ layers through the process of differentation

what is differentation?

the process during which stem cells express specific sets of genes, committing them to a pathway that determines their ultimate cell type

when does organogenesis occur?

following gastrulation, during week 3-8 of human development