Fertilization and Gastrulation Flashcards
follicular cells that cover the egg
Corona Radiata
Glycoprotein meshwork important for zone reaction
Zona Pellucida
Part of the sperm which contains the mitochondria
Middle piece of tail, has mitochondrial sheath
Where does fertilization occur?
ampulla of the fallopian tube
Fertilization, cleavage, formation of blastocyst, formation of inner cell mass (embryoblast), and implantation
Week 1 events (0-7)
occurs in uterus and uterine tubes; glycoprotein coat on the head of sperm is removed allowing for acrosome reaction and passage of sperm through corona radiata
Capacitation (7 hours)
What enzyme is initially released by the sperm to penetrate the corona radiata?
hyalouronidase
Penetration of zona pellucida
esterases, acrosin, and neuraminidase released to penetrate; perivitelline space releases granules to help the zone reaction
Zona reaction
when one sperm breaks through zona pellucida a conformation change occurs to make it more rigid and prevent polyspermy
Perivitelline Space
Where egg cells release granules to help zona reaction
Morula
after 8 cell stage; day 3; 12-32 cells
Morula enters body of uterus and fluid diffuses in, forming a cavity
formation of the blastocyst; day 5
gives rise to placenta
trophoblast
gives rise to embryo
inner cell mass
Releases early pregnancy factor to protect embryo during first 10 days
trophoblast
stem cell layer that is mitotically active
Cytotrophoblast
multinucleate without a plasma membrane; release proteolytic enzymes for implantation chorionic gondatotropin (hCG)
Syncytiotrophoblast
Formation of a bilaminar disc and implantation
Week 2 events
Epiblast (ectoderm, amnion, amniotic cavity) and the hypoblast (only during week 2) derived from:
Inner Cell Mass
Extraembryonic endoderm which gives rise to prechordal plate (fuses to epiblast forming future mouth), primary and secondary yolk sac (umbilical vesicles), and extraembryonic mesoderm
Hypoblast
Hollow cavity outside of embryo
Extraembryonic coelom
Lines the trophoblast and covers the amnion
Extraembryonic Somatic Mesoderm
Lines the yolk sac (umbilical vesicle)
Extraembryonic Splanchnic Mesoderm
from extraembryonic somatic mesoderm; forms at embryonic pole; position changes during development
Connecting Stalk (umbilical cord)
Extraembryonic splanchnic mesoderm derivative; forms in the walls of the yolk sac
Primitive Blood
Extraembryonic somatic mesoderm derivative; also includes cytotrophoblast and syncytiotrophoblast; part of placenta
Chorion
Usually happens in posterior wall of uterus after 6 days
implantation
zygote implants in the wrong area of the uterus; often in the uterine tube and can lead to severe problems
Abnormal Implantation or Ectopic Pregnancy
vaginal bleeding beyond 20 weeks gestation; placenta implants over the internal cervical os; marginal, partial, and total
Placenta Previa
formation of the three germ layers that give rise to all tissues; comes from the epiblast
Gastrulation
Formed from ectoderm
skin, hair, nails, CNS, brain
Formed from mesoderm
connective tissues, bone, muscle, blood, heart, spleen
Formed from endoderm
lungs, GI organs, bladder, glands
Forms in caudal portion of embryo; primitive node/knot at top with the streak coming down
Primitive Streak
Cells at primitive streak meet and are pushed down to form true embryonic endoderm (replacing hypoblast) and mesoderm
Formation of the layers
future diaphragm (rostral)
septum transversum (mesoderm)
future heart (rostral)
cardiogenic area (mesoderm)
Prechordal plate only made up of two layers (no blood supply); future mouth
endoderm and ectoderms
Cloacal membrane only two layers and no blood supply; common membrane for urinary, digestive, and reproductive systems
endoderm and ectoderm
mesoderm from primitive pit towards prechordal plate; template for vertebral column, longitudinal axis for embryo, and induces the formation of neural plate and CNS
Notochord
posterior midline diverticulum from wall of yolk sac; endoderm; template for umbilical arteries and veins; BECOMES URACHUS
Allantois
