Embryology: The Embryonic Period Lecture 3 Flashcards
How many days does it take to get to the uterine lining?
About 7 days
What is the purpose of the synctiotrophohlast?
Used to access glands
What happens during Implantation?
- Trophoblast cells differentiate
- Embryoblast cells differentiate
- Two cavities form
What structures make up the Bilaminar germinal disc?
The hypoblast and epiblast
What layers are in the embryo after implantation?
Epiblast and hypoblast
What layers are in the trophoblast after implantation?
Syncytiotrophoblast and cytotrophoblast
What are the two cavities formed above and below the Bilaminar disc?
Amniotic sac cavity (above)
Yolk sac cavity (below)
Where is the Extraembryonic (XE) Mesoderm found?
Found between inner lining of cytotrophoblast and yolk sac (add drawing pic)
What is the Extraembryonic Mesoderm?
It is a new layer of cells derived from the epiblast and yolk sac. It continues to separate the embryo from surrounding uterine tissue. It gives mechanical and trophic support
What are some reasons a pregnancy ultrasound might be done in the first trimester?
- confirm a normal pregnancy
- Determine age
- Detect problems (ectopic pregnancies, etc)
- Look for twins, etc
- Identify problems with placenta, uterus, ovaries
Why isn’t the fertilized egg susceptible to teratogens during the first two weeks?
The first two weeks aren’t really affected by teratogens because nothing that the mom really ingests can affect it at this stage. It’s not implanted into the mother. Not fully connected yet.
What are the major events to occur during the Embryonic Period?
- All major body systems develop
- 2D disk to 3D cylinder
- Folding of the embryo
- Craniocaudal folding (CNS)
- Lateral folding - amnion/body wall
Why does the folding of the embryo occur?
It happens because the brain grows so quickly that it bends over and folds.
What is gastrulation?
It is the beginning of morphogenesis (developing of body form)
- Forms a trilaminar embryonic disk
- Process that establishes the 3 primary germ layers
What are the 3 primary germ layers and their colors?
They give rise to all tissues and organs
Endoderm - yellow
Mesoderm - red
Ectoderm - blue
What do we get when we cut through a layer of the blastula?
The primitive streak
What is the buccopharyngeal (oropharyngeal) membrane?
It is the future site of the mouth add picture
What is the primitive streak?
It is the future axis of the embryo. If you see the streak, then it means that gastrulation has started.
Match the dorsal and ventral sides of the epiblast and hypoblast
Epiblast is dorsal and hypoblast is ventral
What is the possible connection between conjoined twins and the primitive steak?
So another way to get conjoined twins might be that we get two primitive streaks that don’t separate
How does the primitive streak form?
It forms from the proliferation of epiblast cells
How/which direction does the primitive streak elongate?
The Streak elongates with cells added to the caudal (back) end.
Where is the heart located in the blastula/primitive streak?
The heart is actually at the very top. When the brain starts to bend everything over because of it’s big size, the heart rotates down to where it is now
Where do all the germ layers come from? Give order
ALL of them come from the epiblast
Epiblast - Primitive ectoderm (for ecto) - Primitive Streak (for meso and endo)
What should happen to the primitive streak and what replaces it?
The primitive streak should eventually regress and is replaced by the notochord
What problematic mass can arise if primitive streak does not regress?
A sacrococcygeal teratoma can form
What is a sacrococcygeal teratoma?
- It is a giant non-malignant tumor that forms from remnants of streak.
- Has derivatives and tissue types of all 3 germ layers
- Technically “common” tumor