Bilaminar and Trilaminar embryonic disks Flashcards
inner cell mass
embryoblast
outer cell mass
trophoblast
two layers: cytotrophoblast-mitotic figures
syncitiotrophoblast
syncitiotrophoblast
- secretes hCG 2. used in implantation (chews into the endometrium)
decidual reaction
uterus realizes that embryo has implanted so it sends nutrients to the egg to help it grow and develop
embryoblast fate
becomes epiblast (which becomes everything else, including amnioblasts)
hypoblast
separated by basement membrane
epiblast
pluripotent cell that forms many embryonic cells, such as amnioblasts which form the amniotic cavity and secrete amniotic fluid
fibrin plug
completes the implantation of the embryo into the endometrium (day 10)
lacunae
hypoblast cells begin to multiply and extracellular vacuoles appear in syncitiotroph and join to make the lacunae (blood lake)
genetic imprinting experiments
male csome: regulate embryoblast
femal csome: regulate trophoblast
fate of blastocystic cavity
lined with hypoblast and converts it to the primary yolk sac (first site of hematopoesis)
levels of hCG
double every two days
used to follow normal pregnancy
used to test for pregnancy
chorionic cavity formation
need migration of epiblasts to the extra embryonic mesoderm
forms between yolk sac and cytotrophoblast
primary yolk sac
hypoblast migration transforms blastocyst into primary yolk sac
extraembryonic mesoderm laeyers
splanchic mesoderm surrounds yolk sac somatic mesoderm: -lines the cytotrophoblast -becomes the connecting stalk (umbilicus) (2 weeks)
chorion components
syncitiotrophoblast
cytotrophoblast
extraembryonic mesoderm
(2 weeks)
secondary yolk sac
responsible for hematopoiesis and primordial cell growth
2 weeks
early placenta
utero-placental circulation by the maternal blood lacunae in endometrium and invasion of ST+chorionic villi
Week of 2s
2 trophoblastic layers - cytotrophoblast and
syncytiotrophoblast
2 layers from the inner mass - epiblast and hypoblast
2 yolk sacs - primary and secondary
-2 extraembryonic mesoderms - splanchnic and somatic
-2 future cavities - chorionic and amniotic
-2 components of the placenta - endometrium and chorion
-2 clinical uses of beta hCG
primitive streak
3rd week
has node, pit and groove
establishes position and polarity
dorsal-ventral, right-left, cranial-caudal
buccopharyngeal membrane and cloacal membrane
where epiblast and hypoblast are fused in primitive streak
gastrulation
movement of epiblast cells toward the primitive groove
form definitive endoderm and intraembryonic mesoderm
epiblast cells proliferate and lose adhesions, grow pseudopodia and move toward primitive streak
three layers gastrulation forms
definitive endoderm
intraembryonic mesoderm
trilaminar embryo
all layers derived from epiblast
sacrococcygeal tumor
result of a primitive streak that does not disappear after the 4th week, most common tumor in newborns
fate mapping
the destiny of the epiblast cells depend on what part of the embryo they come from
differentiation of the mesoderm begins cranially and proceeds caudally
mesoderm derivatives
- axial mesoderm
- paraxial mesoderm
- intermediate mesoderm
- lateral plate mesoderm
- mesodermal contribution to the chorion
formation of notochord and neurulation finish in 3rd week
notochord formation
3rd week, from axial mesoderm
formation is a series of steps involving fusing with
the endoderm
-defines primary axis, gives embryo some rigidity
-induces formation of vertebral column
-induces neuroectoderm to form neural plate
-persists as the nucleus pulposus in the
intervertebral disc until early childhood. Likely
replaced by connective tissue
prechordal plate (endoderm)
sets the limit of rote cranial migration of the notochordal cells
induction of the forebrain
neurulation
prechordal plate and notochord induce neural plate formation in the overlying ectoderm
neural plate differentiates to neuroectoderm that forms brain and spinal cord during embryonic period
week of threes
-3 parts to the primitive streak - groove, pit, node
-3 directions imparted by the primitive streak:
dorsal-ventral
right-left
cranial-caudal
-3 definitive germ layers - ectoderm, mesoderm, endoderm
-3 types of villi - primary, secondary, tertiary
