Early Embryogenesis Flashcards
1
Q
embryogenesis
A
- weeks 1-8 of human pregnancy
- organ primordia (first recognized) are established
- embryonic period followed by fetal period
2
Q
first week of embryogenesis
A
- oocyte is fertilized in the ampullary region of the uterine tube
- zygote then undergoes cleavage divisions for form a morula and then a blastocyst
- by the end of the first week, the blastocyst begins implantation into the uterine wall
3
Q
fertilization
A
- results in diploid zygote
- sperm moved to the uterine tube via muscular contractions of the uterine tube and uterus towards ovary
- 30 min or 6 days
- after fusion, male and female pronuclei replicate their DNA and the maternal and paternal chromosomes organize for mitotic division
- the duplicated chromosome sets (23 of each) split to provide each cell of the two cell zygote normal diploid number of chromosomes
- activates cleavage divisions
4
Q
cleavage divisions
A
- mitotic divisions
- reduce the size and increase number of cells
- blastomeres is cell type
- after third cleavage, blastomeres maximize their contact with each other and form a compact ball of cells- compaction
- 3 days after fertilization, the compacted embryo divides to form a 16-cell morula
5
Q
compaction
A
- after 3rd cleavage
- segregates inner cells from outer cells
6
Q
blastocyst formation
A
- inner cells of the morula constitute the inner cell mass
- ICM gives right to tissues in embryo proper and outer cells give rise to the trophoblast that later contributes to the placenta
- fluid then penetrates into the intercellular spaces of the ICM to form a blastocoel
- embryo now blastocytes
- outer cells flatten and form the wall of the blastocyst
7
Q
ICM
A
- pluripotent cells that give rise to embryo
- ESCs
- trophoblast cells contribute to extraembryonic tissues
8
Q
embryonic stem cells
A
- ESCs
- derived from the inner cell mass of the embryo
- pluripotent
- potential to treat a variety of diseases such as diabetes, AD, parkinson’s
- ethical issues since they are harvested from viable embryo
- induced pluripotent cells are alternative and generated from adult
9
Q
trophoblast cells
A
- attach to uterine wall epithelium
- penetrate between the epithelial cells of the uterine mucosa
- recent studies suggest that molecules called L selectins on trophoblast cells interact with carb receptors in the uterine epithelium to mediate attachment of blastocyst
- on day 8, blastocyst partially embedded in endometrium and differentiates into two layers
- cytotrophoblast
- syncytiotrophoblast
10
Q
cytotrophblast
A
- inner layer of mononucleated cells
- stay cell like
11
Q
syncytiotrophoblast
A
- outer multinucleated layer that lacks distinct cells boundaries
- continues to expand into uterine wall
12
Q
bilaminar germ disc
A
- on day 9, ICM differentiates in hypoblast and epiblast
- form flat bilaminar disc
- amniotic cavity forms within the epiblast
- trophoblast invades maternal capillaries to establish uteroplacental circulation
- epiblast gives rise to embryo proper
- -hypoblast and trophoblast contribute to extraembryonic tissues
13
Q
ectopic pregnancy
A
- abnormal implantation
- 2% of all pregnancies
- 9% of all pregnancy related maternal deaths
- 95-95% all in tube
- can occur in ovary, cervix, cesarean scar, abdominal
14
Q
goals of gastrulation
A
- bring inside the embryo areas destined to form endodermal organs
- surround the embryo with cells capable of forming ectoderm
- place mesodermal cells in proper positions in between
- begins with formation of primitive streak on the surface of epiblast
- becomes a narrow groove with a structure called the primitive node surrounding primitive pit at cephalic end
15
Q
invagination
A
- epiblast cells migrate into primitive streak
- epiblast cells migrate toward primitive streak and then detach from epiblast and move through the streak to slip beneath it
- once cells have invaginated, they displace the hypoblast to create endoderm
- other cells lie in between epiblast and new endoderm to form mesoderm
- cells remaining are ectoderm
