1st and 2nd weeks of development Flashcards
Spermatogenesis begins
at puberty
Oogenesis begins
in early fetal life
Where is oogenesis arrested until just before ovulation?
prophase I
Where is oogenesis arrested until fertilization?
metaphase II
What happens in spermiogenesis?
4 haploid spermatids–> 4 sperm
loss of cytoplasm, gain of tail, and formation of acrosome
Process of spermatogenesis
spermatogonium (2N) enlarges to 1* spermatocyte (2N)--> Meiosis I--> two 2* spermatocytes (N)--> Meiosis II--> four spermatids (N)--> spermiogenesis--> 4 sperm (N)
Process of oogenesis
oogonium (2N)
enlarges to 1* oocyte (2N)–>
Meiosis I (fin. at ovulation)–>one 2* oocyte + 1st polar body –>
Meiosis II (fin. at fertilization)–>one mature oocyte + 2nd polar body
Layers of trophoblast
cytotrophoblast + syncytiotrophoblast
Day 7
Cytotrophoblast appearance and structures formed
distinct cells
forms 1* chorionic villi (Day 14)
Syncytiotrophoblast appearance and structures formed
amorphous, indistinct cell boundaries
forms lacunae
produces HCG (Day 10), enters maternal blood through lacunae
Layers of embryoblast (inner cell mass)
hypoblast + epiblast
Hypoblast appearance and structures formed
cuboidal lower layer
forms exocoelomic membrane, which together with hypoblast makes up 1* yolk sac or umbilical vesicle
–>extraembryonic mesoderm
layer becomes endoderm
Epiblast appearance and structures formed
columnar upper layer
forms amnion and amniotic cavity
also forms primitive streak
layer becomes neuroectoderm
Bilaminar embryonic disc
= endoderm + neuroectoderm
formed from hypoblast + epiblast
Day of embryo implantation
Day 10