Embryology: Implantation to Gastrulation Flashcards
Leukemia Inhibitory Factor (LIF)
Needed for blastocyst to implant to endometrial lining, mutations cause infertility
Blastocyst and endometrium must recognize and interface with each other in order for implantation (in order to stick)
Use glycolipids and glycoproteins
Spotting or Implantation Bleeding
Results from blastocyst implanting itself into vascular endometrium with syncytiotrophoblasts
General function of trophoblast
To connect to mother’s blood supply and become placenta
Trophoblast –> Cytotrophoblast and syncytiotrophoblast
General function of embryoblast
To develop into embryo and supporting structures
Embryoblast –> Hypoblast and Epiblast (everything comes from epiblast)
Week 2 Characteristics of Embryogenesis
- Bilaminar Embryonic Disc (Epiblast/Hypoblast)
- Formation of 2 layers in embryo (Epi/Hypoblast)
- Formation of 2 layers in trophoblast (Cyto/Syncytiotrophoblast)
- Formation of 2 cavities above and below bilaminar disk (amniotic sac and yolk sac)
Epiblast differentiation
Epiblast –> Amnion and Amniotic Sac (cavity)
Hypoblast differentiation
Hypoblast –> Yolk sac, yolk sac cavity
What is HCG, where does it come from?
HCG = Human Chorionic Gonadotrophin, secreted from syncytiotrophoblast.
Function is to tell ovary to secrete hormones to maintain pregnancy, rate limiting step.
This is what pregnancy tests are looking for
Once placenta is setup, embryo is exposed to mom’s diet and ingestion
Doesn’t occur until after week 2, dependent on ovum material until then.
Teratogen susceptibility
- If happens during week 1-2 = prenatal death
- If happens during week 3-8, major morphological abnormalities
- After week 8 = CNS defects
Most susceptible during weeks 3-8
Embryo development stages
Week 3: CNS, heart Week 4-5: eye, heart, limbs Week 6: ears, teeth Week 7: palate Week 8: ear, palate, genitalia
Extraembryonic (XE) Mesoderm
- Derived from epiblast
- Envelops embryoblast structures
- Develops into somatic XE mesoderm and splanchnic XE mesoderm
- Functions as mechanical and trophic support
XE Mesoderm mechanism
- XE mesoderm forms
- XE coelom begins as splits in XE mesoderm (then becomes cavity)
- Cavity is called chorionic cavity, connecting stalk becomes umbilical cord
Week 3 characteristics
3 layers of trophoblast: syncytiotrophoblast, cytotrophoblast, XE mesoderm
3 cavities: amnion, yolk sac, chorion
Splanchnic XE mesoderm vs. Somatic XE mesoderm
Splanchnic covers the yolk sac/embryo
Somatic covers the entire structure including the chorionic cavity
Chorionic villus
Becomes placenta, is location for chorionic villus sampling (CVS) to test for genetic defects and diseases
Gastrulation
Beginning of morphogenesis (development of body forms)
3 primary germ layers
- Endoderm (hypoblast)
- Mesoderm (migrating cells from epiblast)
- Ectoderm (epiblast)
Purpose of germ layers
Give rise to all organs and tissues of the adult
Primitive Streak
- Marks beginning of gastrulation
- Determines axis of embryonic development
- Has a mouth (buccopharyngeal) and tail end
- Elongates from tail to mouth –> pit/node
Formation and incomplete separation of 2 primitive streaks can result in conjoined twins
Other way is incomplete division of inner cell mass (embryoblast)
Primitive streak elongates with cells added to caudal end
Cells migrate to the center of the embryo
Mesenchyme
Most primitive connective tissue, results from epiblast cells migrating to become mesoderm
Trilaminar embryonic disk
Endoderm, mesoderm, ectoderm
Also notochord development
Ectoderm
Becomes skin, CNS
Mesoderm
GI tract, intestinal lining
Teratomas
Have pieces from all germ layers
Most common congenital germ cell tumor
Sacrococcygeal Teratoma (SCT)
Predominantly in females. Can intervene in utero and excise.
Germ layer defects
Caudal dysplasia, caudal regression syndrome
Results in underdevelopment to lower limbs, fish tail appearance
Major occurrences in week 3
- Appearance of primitive streak
- Differentiation of 3 primary germ layers
- Development of notochord
Notochord
- Acts as axis for embryo development
- Foundation for vertebral column
- Develops future CNS (neural tube)