Question

MCAT Biology Tutorial: Human Development pt. 2

Answer 1

\({\bf{Fertilization:}}\)
- capacitation: dissolving of the acrosome (see pt. 1 of the human development tutorial) via hydrolytic enzymes
- corona radiata: follicle layer on the egg
- zona pellucida: extracellular matrix on the egg, binds to sperm, releases the enzymes in the sperm

events following fertilization:
- fusion of sperm and oocyte, forming zygote
- release of calcium ions
- cortical reaction: release of enzymes into the zona pellucida, prevents fertilization from additional sperm to preserve chromosome #
- oocyte resumes meiosis II and divides into a polar body + ovum
- DNA replication w/in zygote

Answer 2

\({\bf{Implantation:}}\)
- zygote travels from fallopian tube down to uterus
- forms blastocyst
- implants into endometrium
- uses maternal capillaries for blood supply
- hCG: hormone secreted upon implantation (this is the chemical detected by pregnancy tests)

\({\bf{Placentation:}}\)
- chorionic villi: fetal membrane extensions that form placental disk
- allantosis: forms the umbilical cord
- umbilical cord: delivers nutrients/oxygen/waste/antibodies between placental and embryo
note: the placenta, after ~ 3mos will start producing progesterone and estrogen to replace the degrading corpus luteum --> preparation for lactation

\({\bf{Basic~timeline~of~Development:}}\) (will be going into detail in the next tutorial but for now here's a general overview)
- 40 weeks total, three trimesters of 3 mos each
- first 9 weeks: zygote undergoes mitosis and forms embryo
- second 9 weeks: fetus formation
- 37 weeks: cut-off point for premature births
~ 40 weeks: labor, dilation of cervix, delivery of the baby
note: the placenta/umbilical cord is still attached at birth; after the baby is delivered the placenta will detach and be delivered as well

Answer 3

#thisiswhyimneverhavingkids

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT