Early embryogenesis: limb development Flashcards
What epithelia makes the maternal part of the placenta?
Endometrium
What are the phases of the menstrual cycle?
Menstrual phase: 1-4
Proliferative/follicular phase: 5-14
Secretory/luteal phase: 15-28
Implantation often occurs on day ___.
21
Ovulation often occurs on day ____.
14
What are the 2 different aging systems for a fetus?
- Fertilization (conception) age: dates pregnancy from the time of fertilization
- Menstrual/gestational/clinical age: used by clinicians and dates the pregnancy from the woman’s last period. 2 weeks greater than fertilization age.
By day ___ of development, all cells for organ systems are in place.
56
What is the most sensitive stage of development?
Week 3
What is the embryonic stage?
First 8 weeks
Zygote formation
Cell division
Implantation
Organ formation
What is the fetal stage?
Week 9-birth
Are there any birth defects associated with weeks 0-2?
Nope!
What is the window of fertilization?
1-2 days after ovulation
When does implantation occur?
Day 6-7
The blastocyst is composed of ____ and ____.
ICM and ECM
What is the outer cell mass called? What does it develop into?
Trophoblast, extra-embryonic tissues (e.g. placenta)
What is the inner cell mass called? What does it develop into?
Embryoblast, embryonic cells and layers
What is the most common site of ectopic pregnancy?
Ampulla
What is the usual site of implantation?
Posterior superior wall
What 2 layers does the trophoblast divide into upon implantation?
- Cytotrophoblast
2. Syncytiotrophoblast
What does syncytiotrophoblast secrete?
hCG to maintain pregnancy (acts on embryo)
What is the decidua?
The name for a pregnant endometria. The cells become larger and rounder and filled with glycogen and lipids
What 2 cell layers does the embryoblast divide into?
- Epiblast - DORSAL layer
- Hypoblast - VENTRAL layer
The hypoblast does NOT contribute to the cells of the developing embryo
What makes the yolk sac and what does it store?
Made from hypoblast. Contains nutrients for development.
What makes the amniotic cavity?
Made from epiblast
What are sources of amniotic fluid?
Amnion cells
Maternal tissues
Fetal urine
How many L of amniotic fluid accumulate by 33 weeks?
1
What causes polyhydramnios (too much amniotic fluid)?
Insufficient fetal swallowing
What causes oligohydramnios (too little amniotic fluid)?
Renal agenesis
When does gastrulation occur?
Week 3
In gastrulation, the cells of the _______ migrate and change shape slipping into the ______ groove.
Epiblast, primitive grove
Hypoblast is now gone!
The primitive grove forms on the ______ side and the _____ end.
Dorsal side, caudal end
What order do the layers of gastrulation form?
Endoderm
Mesoderm
Ectoderm
Gastrulation mistakes can lead to what kind of tumor?
Sacrococcygeal teratoma
What important structure forms at week 3? What is its adult remnant?
Notochord, nucleus pulposus
What tissue layer forms the nervous system?
Ectoderm
What is the precursor of the primordial cns?
Neural plate
In what week do the neural tube pores close? Which is first?
Cranial first then caudal in week 4
What is meroanencephaly?
Failure of rostral neuropore to close during the fourth week, forebrain development is abnormal
What nutrient can cause neural tube defects when levels are inadequate?
Folic acid
What cells migrate into the mesenchyme once the neural tube forms (becomes cylndrical)?
Neural crest cells
What cells and tissues do neural crest cells give rise to?
PNS and bones (facial skeleton, skull, etc.)
What is the paraxial mesoderm?
Condensation of mesoderm lateral to the notochord. Organizes into somitomeres in the head. Age of embryo can be related to number of somites.
What do somites give rise to?
Segmental bone (axial skeleton) (sclerotome) Skeletal muscle (myotome) Dermis/connective tissue for back (dermatome)
Each myotome and dermatome has its own segmental nerve component that ______ with the cells.
migrates
What system does the intermediate mesoderm give rise to?
Urogenital system
What is the somatic/parietal mesoderm layer?
Layer adjacent to the body wall
What is the splanchnic/visceral mesoderm?
Lines the gut
What causes the formation of the body cavity?
Splitting of the lateral plate mesoderm.
What is the function of the head fold?
Move the heart and other organs below the oropharyngeal membrane
All of the epithelia lining the gut is formed from what?
Endoderm
What is omphalocele?
Failure of intestine to return to the body. Covered by amnion
What is gastroschisis?
Protrusion of the viscera into the amniotic cavity due to abnormal closure of the body wall.
Limbs will have developed by the end of week ____.
8
Upper extremity development takes place 2 days _____ lower extremity.
Before
What is the apical ectodermal ridge (AER)?
A distal tip of ectoderm that signals for a limb bud to form into a full limb
What gives rise to the limb bones, cartilage, and connective tissue?
Lateral plate mesoderm. Mesenchymal cells laying down cartilage followed by ossification
What gives rise to skeletal muscle?
Paraxial mesoderm
What gives rise to melanocytes and schwann cells?
Neural crest cells
