Week 3 Development Flashcards
Is pregnancy detectable in the 3rd week?
yes, by ultrasound
What does the 3rd week of development coincide with?
- coincides with 1st week after missed menstrual period
- embryo is already 2 weeks old
- 5 weeks after last normal menstrual period (LNMP)
Where is the epiblast?
adjacent to amniotic cavity
where is the hypoblast?
adjacent to umbilical vesicle
Where is the prechordal plate?
thickened circular area of columnar hypoblast cells
The prechordal plate will eventually form what?
- organizes development of the head region
- future site of the mouth
What is the outcome of gastrulation?
establishes axial orientation in embryo
What does morphogenesis mean?
development of the body form begins now
Where does the primitive streak appear?
thickened median linear band on the dorsal and caudal surface of the epiblast (first sign of gastrulation)
What is causing the primitive streak to form?
forms as epiblast cells proliferate and migrate to the median plane
What orientation landmarks are established in the primitive streak?
primitive node, primitive pit, primitive groove
Where is the primitive node?
Accumulated epiblast cells at the cranial end of the primitive streak
Where is the primitive pit?
small depression in the primitive node
Where is the primitive groove?
- narrow depression oriented lengthwise within the primitive streak
- the pit and groove form as epiblast cells migrate inward through the primitive streak
How is embryonic endoderm formed?
as a result of epiblasts migrating inward through the primitive streak some epiblast cells displace the original hypoblast cells
What is the embryonic mesoderm?
as a result of epiblasts migrating inward through the primitive streak some epiblast cells take up position between the epiblast and the original hypoblast
- become mesoblasts which will form the embryonic mesoderm
What is mesenchyme?
a rudimentary connective tissue
Where does mesenchyme migrate?
migrate laterally to reach extraembryonic mesoderm of umbilical vesicle & amnion
How does mesenchyme relate to extraembryonic mesoderm?
as a result of epiblasts migrating inward through the primitive streak some epiblast cells from embryonic mesoderm and others form mesenchym
Where is the cardiogenic area?
- What will develop here?
mesenchyme will migrate cranially on either side of the prechordal plate into cardiogenic area
- site where the heart begins developing
What cell types develop from mesenchyme?
highly migratory cells which become fibroblasts, chondroblasts, osteobasts
- mesenchyme can also form ectoderm and endoderm
What is embryonic ectoderm?
the remaining epiblast cells which migrated inward through the primitive streak become the embryonic ectoderm
When does mesoderm production diminish?
early week 4
When does the primitive streak degenerate?
disappears by end of week 4