Gastrulation and Germ Layers Flashcards
When is something most likely to go wrong in human development?
First 7 weeks
What is the Zona Pellucida?
a thick layer of glycoproteins surrounding the oocyte.
Helps with sperm recognition.
What are granulosa cells? What types are there?
They are responsible for follicle development
Cumulus oophorous: anchor oocyte to follicle wall.
Mural granulosa cells: line wall of follicle
Corona Radiata: firmly anchored to ZP
What is the Acrosome reaction?
sperm head releases enzymes to pass CR and ZP
Need to go ‘across’ 2 layers
What is Zona reaction?
changes in ZP making it impermeable to other sperm cells. Prevents dispermy
(Creates a ‘zone’)
What marks the beginning of human development?
pronuclei fusing to create a zygote
When does cleavage begin? What happens?
30 hrs after fertilization
Zygote cleaves –> blastomere (2 cells w 2 polar bodies)
When/ why does compaction begin (#of cells)?
9 cell stage. Because ZP is restricting further growth
What is a morula?
when compaction stops ~32 cells
(mulberry)
Day 3
How does a blastocycst cavity form? What makes up new blastocyst?
After morula enters uterus, it absorbs fluid and creates blastocyst cavity
Early Blastocyst: has embryo and its membranes
- trophoblast (surrounds blast. cavity)
- embryoblast (inner cell mass)
When does the ZP degenerate? What happens?
After ~4-5 days, the blastocyst ‘hatches’
It forms later blastocyst
Where does fertilization occur?
Ampulla (distal 2/3 of uterine tube)
What is spontaneous abortion?
when zygotes, morulae, and blastocysts abort
~45% of fertilized ovums (before you know you know you’re preggo)
Causes: Chromosomal anomalies (segregation, duplication, deletions, dispermy)
-Low progesterone & estrogen from corpus luteum
When does implantation occur?
day 6-8
What happens to the trophoblast before it can implant?
Differentiate to cytotrophoblast and syncytiotrophoblast
What are syncytiotrophoblasts and what do they do?
differentiated trophoblast. Multiple nuclei. Invade endometrium with enzymes.
Allows blastocyst to ‘burrow’ into endometrium
What does the embryoblast become? and when?
epiblast and hypo blast
day 7
What does the hypoblast do? Where is it?
Forms exocoelomic membrane (future yolk sac).
It is continuous inner lining wih the exocoelomic membrane. Lies just behind epiblast.
What does the epiblast form?
It forms the amniotic cavity by making a separation in the epiblast.
The amnion encloses the embryo and house amniotic fluid.
What makes up the bilaminar disk?
Hypoblast & Epiblast
What is the primary umilical vessel? When does it form?
When the (newly formed) extraembryonic mesoderm begins to compress, the hypoblast + lining of exocoelomic membrane form the primary umbilical vessical. Day 10-12
What is the secondary umbilical vessel? When does it form?
Extraembryonic coelom pinches of remnant (primary vessicle), leaving behind 2ndary umbilical vessicle.
- Originate from hypoblast
- Site of primordial germ cells
Day 13
What does the extraembryonic somatic mesoderm line?
trophoblast and amnion
What does the extraembryonic splanchnic mesoderm line?
umbilical vessical
What is the chorionic sac?
fetal component of placenta
extraembrionic somatic mesoderm + syncytiotrophoblast
What is an ectopic pregnancy? Where do they typically happen?
Implantation of blastocyst outside the uterine cavity
2% of all pregs
95% of them happen in oviduct (proximal uterine tube)
When does gastrulation begin? What starts gastrulation?
week 3
forming of primitive streak
over by week 4
What is gastrulation
Epiblast migrate –> Ectoderm + Mesoderm + Endoderm
It defines all the body axes
What do epiblasts migrate through to form germ layers?
The primative streak. They move Cephally and Laterally
What is Sacrococcygeal Teratoma? Why does it form?
Germ cell tumor derived from primitive streak.
When gastrulation exceeds 4 weeks.
1:35,000 live births (80%female)
How does the notochordal process form?
- cranial extension from primitive node
- begins hollow tube (early notochordal process)
- Grows in mesoderm until reaching prechordal plate
- Complete by day 20
What is the notochord?
Mesodermally derived rod
From oropharyngeal membrane to primitive node
Signaller for early embryo
Future nucleus pulposus
What is the caudal eminence?
Temporary Tail (tail bud) made from mesodermal cells Gives rise to caudal structures of body Contribute cells to caudal end of neural tube and NCCs
Ectoderm Derivatives
- Epidermis (skin hair nails etc.), nervous system,
Mesoderm Derivatives?
Muscle, bone, blood, heart
Endoderm Derivatives
Lungs, GI tract, bladder, liver, pancreas
What layer does epithelia come from?
ALL LAYERS
What are the extraembryonic membranes?
2ndary umbilical vessical, amnion, and chorion
