Embryology Flashcards
Where is primary oocyte arrested
prophase I of meiosis I, released by surge of LH
what cells release what protein to keep primary oocyte arrested
granulosa cells secrete OMI
order of hormone surges, from where released and ensuing events
- FSH from pituitary gland stimulates granulosa cells around primary oocyte to enlarge, transform, and start secreting estrogen
- sufficient estrogen levels cause LH surge from pituitary gland –> primary oocyte to secondary oocyte (then ovulation)
- ruptured follicle –> corpus luteum: secretes progesterone to arrest growth of endometrium
- if implantation occurs, hCG from syncytiotrophoblast, prevents corpus luteum from breaking down to secrete progesterone until placenta takes over
FSH
from pituitary –> granulosa cells to secrete estrogen
LH
from pituitary in response to high estrogen level –> primary oocyte to secondary oocyte
progesterone
from corpus luteum, arrests endometrium growth
hCG
from syncytiotrophoblast, prevents corpus luteum from degenerating so it can keep producing progesterone
zona pellucida
contains sperm receptors, acrosomal reaction must happen for sperm to penetrate it
corona radiata
sperm get capacitated in uterus, only capacitated sperm can penetrate corona radiata
Events when oocyte and sperm cell membranes fuse
- cortical reaction to prevent polyspermy (hardening of zona pellucida)
- second meiotic division completed
- egg is activated to prepare for early embryonic events
where is secondary oocyte arrested
metaphase II of meiosis II, released by fertilization
zona pellucida function in embryo transport
hardened zona pellucida prevents embryo from adhering to uterine tube
End of week two after fertilization
firm attachment to lining of endometrium, trophoblast –> cytotrophoblast and syncytiotrophoblast (hCG)
embryoblast –> epiblast (embryo proper) + hypoblast (yolk sac)
*bilaminar embryo composed of opposed layers of epi and hypoblasts
Hyboblast gives rise to…
- extraembryonic mesoderm
2. yolk sac
Cleavage/Differentiation events
- Blastomeres = totipotent
- compaction = inner cell mass and outer
- 16 cell morula = embryoblast + trophoblast
–> Embryoblast cells pluripotent - trophoblast releases fluid to form blastocyst/blastula
- once in uterine cavity:
trophoblast –> cytotrophoblast + syncytiotrophoblast
embryoblast –> epiblast + hypoblast
compaction
prior to this event, all blastomeres are totipotent. After, only embryoblast cells are pluripotent (ESCs of research)
dizygotic twins
result of fertilization of two mature oocytes
monozygotic twins
splitting of embryo during cleavage
fertilization age vs. menstrual age
menstrual age is about 2 weeks greater than fertilization age. Parturition normally happens at 38 wks fert age and 40 weeks menstrual age
Gastrulation - week 3
- formation of primitive streak
- endoderm first wave, mesoderm second wave, never ingress are ectoderm
- primitive streak regresses at day 18
buccopharyngeal and cloacal membranes
only place where there is an interface between endoderm and ectoderm, no mesoderm
primitive node
forms notochord and prechordal plate (both mesoderm)
prechordal plate releases what
Shh to induce forebrain
- Shh gene mutations lead to hyper-/hypotelorism
prechordal plate and notochord functions
signaling for development of nervous system, face, and axial skeleton
paraxial mesoderm/somites forms…
dermis, skeletal muscle, bone, cartilage, axial skeleton
intermediate mesoderm forms…
genitourinary organs
lateral plate mesoderm forms…
- somatic layer (in contact with ectoderm): forms anterior body wall
- splanchnic (in contact with endoderm): forms gut tube
ectoderm immediately adjacent to notochord
form neural plate, then neural tube that dissociates
neural crest cells
PNS, melanocytes, adrenal medulla, pharyngeal arches
Cranio-caudal folding
- head fold: heart in correct position, incorporates yolk sac as part of foregut
- tail fold: incorporates park of yolk sac as hindgut
pharyngeal arches
formed by neural crest cells, surround foregut, building blocks of anterior head and neck
1-4, 6
Shh signaling, RA
polyhydramnios vs oligohydramnios
excess, deficiency
lateral folding
splanchnic and somatic folds of lateral plate mesoderm fold to form gut tube and anterior wall of abdomen, respectively
rhombencephalon
hindbrain, affected by RA
Rhombomeres are specified by Hox genes and contain RAREs (RA response elements)
embryo veins
- umbilical: only one, O2 to caudal end of heart tube
- vitelline: deO2 from yolk sac
- cardinal: deO2 from body
Where are RBCs formed?
1. extraembryonic mesoderm of yolk sac 28 days: aorta mesoderm 6-8 weeks: liver 12 weeks: spleen 4 months: marrow starts 6 months: all marrow
Embryonic period
Weeks 3-8 (organogenesis), critical period when most susceptible to teratogens
Fetal Period
Weeks 8-38
Fetal Development - week 8
tail disappears
FD - week 9
gender specific
FD - week 12
can indicate sex
FD - month 4
lanugo on head, sucks thumb
FD - month 5
lanugo on body, vernix caseosa
FD - month 6
dark lanugo, surfactant
FD - month 7
CNS mature enough for survival
FD - month 9
lanugo shed, lots of surfactant
When is greatest fetal length increase?
4-5 months
When does weight significantly increase?
7 months
