12 Gastrulation, Notochord & Neurulation Flashcards

During week 3, the embryonic disc changes from having two layers to three layers; this process produces the

Trilamimar disc

When somites disappear

• First occipital

• Last 5–7 coccygeal

A linear thickening appears in the epiblast near the future tail region and marks the beginning of gastrulation. This structure first forms at the ______ end of the embryo.

Caudal

During gastrulation, the first epiblast cells that migrate inward displace the hypoblast and form the definitive ______.

endoderm

A second wave of migrating epiblast cells spreads between the newly formed endoderm and the overlying ectoderm to form the intraembryonic ______.

mesoderm

After some epiblast cells migrate inward to form endoderm and mesoderm, the cells that remain on the surface become ______.

Ectoderm

A midline rod of mesodermal tissue develops from the primitive node and helps establish the body axis; this structure is the

Notochord

The notochord sends inductive signals to the overlying ectoderm, causing it to thicken and form the ______ plate.

Neural

The neural plate later folds to form the ______ tube, which gives rise to the central nervous system.

Neural

The adult structure that remains from the embryonic notochord is the ______ pulposus of the intervertebral disc.

Nucleus

A key signaling molecule secreted by the notochord that helps pattern surrounding tissues is ______.

SHH / Sonic hedgehog

A defect in signaling from the notochord can impair formation of the neural plate because the notochord normally induces overlying ectoderm to become ______ tissue.

Neural / neuroectodermal tissue

The primitive streak allows epiblast cells to migrate inward, making the ______ the source of all three germ layers.

Epiblast

The three germ layers formed during gastrulation are ectoderm, mesoderm, and ______.

Endoderm

The notochord establishes the embryonic midline and helps define the ______ body axis.

Cranial-caudal / anterior-posterior

The primitive node is located at the cranial end of the primitive streak and gives rise to the ______ , which later forms the notochord

Notochordal process

Around day ______, the notochord helps differentiate mesoderm into paraxial, intermediate, and lateral mesoderm.

20

Between days ______ and ______, the neural plate, neural groove, and neural folds join to form the neural tube.

22 and 28

Early neurulation, including neural plate formation and folding, begins approximately between days ______ and ______

18 & 21

The first pair of somites appears in the occipital region around day

20

The neuropores should close by the end of week ______.

4

Failure of neuropore closure by the end of week 4 can result in a persistent connection between the amniotic cavity and the ______ canal.

spinal

The cranial bilaminar region contributes to the ______ membrane, which later forms the mouth.

Oropharyngeal

The caudal bilaminar region contributes to the ______ membrane, which later contributes to the anus and genitourinary tract.

Cloacal

The cloacal membrane disintegrates around week ______.

7

Limb buds first appear near the end of week ___

4

The embryo is especially susceptible to teratogens during weeks

3 to 8

Neural tube formation occurs during weeks ______ to ______.

3 to 4