ME: 1st week of embryo - fertilization to implantation

What are the male and female pronuclei, and when do they appear during fertilization?

the nuclei of sperm and oocyte before fusing. they appear before fusion of genetic material but after sperm entry.

What reaction prevents polyspermy after the sperm fuses with the oocyte?

the cortical reaction, corical granules are released that make the zona pelucida impermeable to other sperm

What triggers the completion of the second meiotic division of the oocyte?

entry of the sperm nucleus into the cytoplasm

name de steps of fertilization

1. sperm reaches zona pellucida

2. acrosomal reaction, acrosome enzymes released to disolve zona pellucida

3. fusion of sperm and oocyte membrane

4. entry of sperm nucleus into oocyte cytoplasm

5. cortical reaction, zona pellucida becomes impermeable to block polyspermy

6. oocyte completes meiosis II

7. pronuclei fuse (form then fuse) → formation of a diploid zygote

What is the morula and at what stage does it form?

solid ball of cells, forms during cleavage

What is the role of E-cadherin in early development?

faccilitates cell-cell adhesion during compaction

What causes the formation of the blastocoel?

fluid filled cavity is formed by Na+/K-ATPase pumps that pump Na+ into the embryo, water follows through osmosis

What is the difference between the embryoblast and the trophoblast?

embryo blast = inner cell mass → embryo proper

throphoblast = peripheral outer cell layer → placenta (dus provides nutrients) & membranes

What is the function of the zona pellucida and what happens to it during blastocyst formation?

it protects the zygote from hatching

When does implantation typically begin after ovulation?

6-10 days after (av = week)

What are the two layers of the trophoblast after implantation begins?

1. cytotrophoblast

2. syncytiotrophoblast (invades uterine lining, secretes hCG)

What are the two layers of the inner cell mass (embryoblast) after implantation begins?

1. epiblast (outer layer)

2. hypoblast (inner layer)

Which structure will eventually become the placenta? (tip: take invasive)

syncytotrophoblast

What is the embryonic and abembryonic pole?

embryonic pole is were inner cell mass is located, abembryonic pole is oposite side

What is an ectopic pregnancy and when can it occur

ectopic pregnancy is when the embryo implants outise the uteris (i.e., in fallopian tube, oveary, mesentery)

Which hormone secreted by trophoblasts is used in pregnancy tests?

hCG