Early Embryology Flashcards
decreased AFP seen with what syndrome
downs syndrome
three periods based on fertilization age
0-3 weeks: early embryo
3-8 weeks: embryonic organogenesis
8-38 weeks: fetal period
major events week 1
cleavage
morula enters uterus
zona pellucida breaks down
blastulation
two layers of blastocyst
embryoblast and trophoblast
implantation occurs when
5-6 days after fertilization
decidua
endometrium of pregnancy
trophoblasts turns into what two layers
cytotrophoblast (mitotically active inner layer)
and syncytiotrophoblast (adjacent to maternal blood supply, produces hCG)
hydatidiform moles
2 types
- complete: fertilization of empty oocyte, fetus is entirely missing
- partial: oocyte with two sperm (or diploid sperm)
causes high hCG, severe nausea and vomiting, vaginal bleeding, spontaneous abortion
major events week 2
embryoblast changes into epiblast and hypoblast
2 cavities form: amniotic cavity and primitive yolk sac
extraembryonic mesoderm forms between yolk sac and cytotrophoblast (which then makes chorionic cavity)
(trophoblast has greater growth than embryoblast)
two sections that embryoblast transofrms into
epiblast (inner, columnar cells related to amniotic cavity)
hypoblast (outer cuboidal cells adjacent to yolk sac)
two layers of extraembryonic mesoderm
somatic: lines trophoblast and amnion
splanchnic: lines yolk sac
3 layers of chorion
- extraembryonic somatic mesoderm
- cytotrophoblast layer
- syncytiotrophoblast layer
oligohydramnios
low volume (<500mL) of amniotic fluid
- Causes
- low placental blood flow
- renal agenesis or obstructive uropathy
- complications (Potter Sequence)
- pulmonary hypoplasia
- facial defects and limb defects
- compression of umbilical cord
polyhydramnios
high (>2L) amniotic fluid
- Causes:
- fetus does not swallow usual amount of fluid (CNS anomalies)
- esophageal atresia
- complications:
- premature rupture of membranes/premature birth
- intrauterine growth restriction
major events week 3
- gastrulation
- epiblast cells become motile and converge on the midline of dorsal disc forming primitive streak
- primitive groove makes opening for cells to migrate ventrally
- thickening at end forms primitive node and pit
- epiblast layer gives rise to 3 germ layers
3 germ layers of epiblast
- Endoderm: epiblast cells that replace entire hypoblast layer
- Mesoderm: from cells that migrate between existing layers
- Ectoderm: cells that remain in epiblast after gastrulation completes
sacrococcygeal teratoma
forms from primitive streak persists longer than it should, causing cell proliferation and tumor formation in sacral area
notochord develops from
migrating mesoderm cells
direction of neural tube closure
cranial to caudal (and cranial end closes ~2 days before caudal end, during week 4)
derivatives of surface ectoderm
- epidermis, nails, hair, subcutaneous glands, mammary glands, anterior pituitary, enamel, lens of eye
derivatives of neural ectoderm
CNS, retina, posterior pituitary gland, pineal body
paraxial mesoderm
- organizes into somitomeres in head region (then into somites, number correlates with age)
- each somite has its own sclerotome, myotome, dermatome
- gives rise to majority of axial skeleton (vertebal column, base of skull, ribs)
intermediate mesoderm
gives rise to urogenital system
lateral plate mesoderm
makes body (somatic mesoderm and overlying ectoderm) wall and gut wall (splanchnic mesoderm and underlying endoderm)
forms bones of limbs, sternum, pelvic girdle and shoulder girdle (appendicular skeleton)
what makes gut (fore/mid/hind)
endoderm (and yolk sac in hindgut)
meckels diverticulum
aka ileal diverticulum
- most common congenital defect of GI system
- due to persistence of vitelline duct
- no symptoms (but can contain ectopic gastric or panceatic mucosa)
embryological sources of bone are
paraxial mesoderm
lateral plate somatic mesoderm
neural crest cells (ectomesenchyme)
which skull bones by neural crest cells
frontal, sphenoid, squamous temporal, nasal, lacrimal, zygomatic, maxilla, incicive, mandible
which bones arise via intramembranous ossification and when
majority of bones of face and flat bones of skull, clavicle
end of week 7 of development
what bones arise via endochondral ossification
long bones of extremities, pelvic and shoulder girdle, vertebral column
time frame of endochondral bone formation
- 6 weeks: hyaline cartilage bone model forms
- 8-12 weeks: primary centers of ossifaction are formed
- 38 weeks: some secondary centers of ossification are present
- after birth: most secondary centers of ossification are formed
