Gastrulation, Neurulation, and Somitogenesis

Fill-in-the-blank flashcards covering key concepts of epithelial–mesenchymal transitions, gastrulation, notochord and neurulation, neural tube defects, neural crest derivatives, embryonic folding, somitogenesis, lateral plate mesoderm derivatives, and associated clinical correlations.

During an _ transition, epithelial cells lose polarity and adhesions to become migratory mesenchymal cells.

epithelial-to-mesenchymal (EMT)

A _ transition converts loosely connected mesenchymal cells into polarized sheets or tubes of epithelial cells.

mesenchymal-to-epithelial (MET)

Formation of the _ marks the start of gastrulation.

primitive streak

Epiblast cells that ingress and displace the hypoblast become definitive _.

endoderm

The three primary germ layers produced by gastrulation are , , and _.

ectoderm; mesoderm; endoderm

The cranial end of the primitive streak expands into the _ , which helps establish the embryo’s longitudinal axis.

primitive (Hensen’s) node

Failure of the primitive streak to regress can lead to a _ teratoma.

sacrococcygeal

Abnormal left-right axis formation during gastrulation can result in _, a mirror-image arrangement of organs.

situs inversus

Inadequate caudal mesoderm production may cause _ (caudal dysgenesis), characterized by limb fusion.

sirenomelia

Mesenchymal epiblast cells that migrate cranially through the node form the _ process, precursor to the notochord.

Notochordal (prechordal)

The adult remnant of the notochord is the _ of the intervertebral disc.

nucleus pulposus

The notochord secretes NOGGIN and CHORDIN to inhibit _ signaling and induce neural plate formation.

BMP

The lateral edges of the neural plate elevate to form the _ and central _.

neural folds; neural groove

Neural tube closure proceeds bidirectionally, leaving temporary openings called cranial and caudal _.

neuropores

The cranial neuropore normally closes on day _ of development.

25

Failure of cranial neuropore closure leads to _, characterized by absent major portions of the brain.

anencephaly

A skull defect with herniated brain tissue caused by failed cranial neuropore closure is called an _.

encephalocele

Failure of the _______ between days 22-28 produces spinal bifida.

Caudal neuropore to close

Neural crest cells originate at the tips of the ____ and migrate widely to form structures such as _ cells of the adrenal medulla.

neural folds, chromaffin

, , and _ all derive from the neural crest.

Melanocytes, Schwann cells, and conotruncal heart

Rapid growth of parietal mesoderm and ectoderm drives _ folding, forming the __.

lateral, ventral body wall

Rapid expansion of the forebrain produces _ folding, relocating heart and septum transversum into the thorax.

cephalocaudal

Early paraxial mesoderm segments into epithelial spheres called _.

somites

Each somite splits dorsoventrally into a _ and a ventral _ that forms vertebrae and ribs.

dermomyotome, sclerotome

Cells at the _ and _ edges of the dermomyotome become _, precursors of skeletal muscle.

medial & lateral, myotome

Muscle derived from myotome cells that stay near the neural tube is called _ (back and intercostal muscles).

primaxial

Myotome cells crossing the lateral somitic frontier into parietal lateral plate form _ muscles (limb & body wall).

abaxial

The line separating somite tissue from lateral plate mesoderm is the _.

lateral somitic frontier (LSF)

Splitting of lateral plate mesoderm creates a dorsal _ layer and a ventral _ layer.

parietal (somatic); visceral (splanchnic)

The parietal lateral plate plus ectoderm forms the _, precursor to the ventral body wall.

somatopleure

The visceral lateral plate with endoderm forms the _, precursor to the gut wall.

splanchnopleure

Failure of parietal lateral plate closure can cause _, an anterior body-wall defect with exposed viscera.

gastroschisis

The __ contributes to adult structures such as the sternum and limb bones.

parietal lateral plate

Head mesoderm (prechordal plate) does not segment into somites but collaborates with neural crest to form the _ skeleton.

craniofacial