embryogenesis Flashcards
embryonic period of development
weeks 3-8
fetal period of development
- week 9 => term
- mainly growth; also brain and nervous development
morula
- after the 8 cell stage
blastocyst
- weeks 1-2 of development
- trophoblast + blastocyst cavity + inner cell mass
trophoblast
- outer cell layer of the blastocyst
- simple squamous epithelium
inner cell mass
- inner part of blastocyst
- will form embryo
ectopic pregnancy
- normal implantation = posterior upper uterine wall
- ectopic sites: tubal, abdominal, ovarian, cervical
chorionic villi
- fetal contribution to the placenta
- on the side of the blastocyst that implants
implantation
- blastocyst (inner cell mass end) attaches to uterine epithelium
- trophoblast (syncytiotrophoblast) invades the endometrium
decidua basalis, capsularis, and parietalis
- layers of the endometrium that shed
- basalis = maternal component of placenta; engaged with villous chorion
- capsularis = overlies smooth chorion
- parietalis = uninvolved uterine mucosa (front wall of uterus)
placenta
- chorionic villi bathed in maternal blood from the decidua basalis
- site of maternal/fetal exchange
- early placental membrane: syntrophoblast, cytotrophoblast, connective tissue, endothelium of blood vessels
- late placental membrane: syntrophoblast, endothelium
umbilical cord
- comes from the connecting stalk
chorionic villi
- fetal contribution to the placenta
- on the side of the blastocyst that implants
- layers of the placental villi are the layers of the chorion (syntrophoblast, cytotrophoblast, mesenchyme)
- most villi are free (coated with syntrophoblast) and are sites for metabolic exchange, but anchoring villi span the thickness of the placenta to desidua basalis
bilaminar embryo
- epiblast => embryo
- hypoblast => outer structures
amnion
- amnion cavity forms when inner cell mass becomes hollow around time of implantation
- consists of ectoderm and extra-embryonic mesoderm
chorion (smooth and villous)
- outermost membrane of blastocyst
- consists of: syntrophoblast, cytotrophoblast, and extra-embryonic mesoderm
- smooth chorion covers amnion
- villous chorion contains the villi that become the placenta
yolk sac
- forms on day 10
- consists of: endoderm and extra-embryonic mesoderm
- provides early nutrition
ectoderm
- comes from epiblast
- surrounds amniotic cavity
endoderm
- surrounds yolk sac
mesoderm
- comes from primitive streak/node and the ectoderm
- forms notochord along the midline then spreads outward to engage extra-embryonic mesoderm
- begins as loss connective tissue (mesenchyme) then condenses to form several columns
mesenchyme
= extra-embryonic mesoderm
embryonic loose connective tissue
gastrulation
- occurs with appearance of intra-embryonic mesoderm
primitive streak
- streak of thickening ectoderm arising behind the primitive knot (mesoderm)
- goes on to form the intra-embryonic mesoderm
notochord
- condensed mesoderm (epithelial columns)
- induces neural plate
- remains as nucleus pulpois of intervertebral disks
paraxial mesoderm
- condensed mesoderm (epithelial columns)
- will form somites for bone, muscle, connective tissue
intermediate mesoderm
- condensed mesoderm (epithelial columns)
- will form UG system
lateral plate mesoderm
- condensed mesoderm (epithelial columns)
- future body wall and cavities and gut wall
coeloms
- intraembryonic coelem forms as the lateral plate mesoderm and cardiogenic mesoderm form a u shape down the middle of the embryo
- will form the pleural, peritoneal, and pericardial cavitieis
somatopleure
- ectoderm and mesoderm from lateral plate
- will form lateral and ventral body wall (including parietal pleura and peritoneum)
splanchnopleure
- endoderm and mesoderm from lateral plate
- will form visceral structures including the gut
week 4
- formation of somites, neural tube, and intra-embryonic coelem
- 3 layered disk => cylinder shape
amniotic fluid
- allows movement of fetus
- initially comes from mother; later is fetal urine which is recycled
- too little: renal agenesis
- too much: inhibition of absorption or swallowing
week 3
- gastrulation occurs with appearance of 3rd germ layer (intra-embryonic mesoderm)
- elongation of the embryonic disk
- neuralation
allantois
vestigial extra-embryonic membrane formed from yolk sack
week 1
ovulation, conception, and migration down uterine tube
zygote => morula
week 2
implantation and extraembryonic membrane formation
morula => blastocyst
- embryo becomes bilaminar disk
- syntrophoblast + cytotrophoblast + extra embryonic mesoderm => amnion, yolk sac, chorion
