Gastrulation, Neurulation & Somitogenesis – Fill-in-the-Blank Flashcards

Fill-in-the-blank flashcards covering key facts on embryonic cell transitions, gastrulation, notochord, neurulation, neural crest, embryonic folding, somite formation, lateral plate derivatives, and associated congenital anomalies.

In the embryo, tightly connected cells that form sheets or tubes are called __ cells.

epithelial

Loosely connected, migratory embryonic cells that form connective tissue matrices are __ cells.

mesenchymal

During an -to- transition (EMT), epithelial cells lose polarity and adhesions to become invasive.

epithelial, mesenchymal

The reverse of EMT, when migratory cells form polarized sheets, is called __ (MET).

mesenchymal-to-epithelial transition

Formation of the marks the beginning of gastrulation.

primitive streak

The cranial end of the primitive streak expands into the __ (Hensen’s) node.

primitive

Epiblast cells that displace the hypoblast form the definitive __ germ layer.

endoderm

Epiblast cells that remain after gastrulation become the __ germ layer.

ectoderm

The three primary germ layers are ectoderm, __, and endoderm.

mesoderm

Failure of proper left–right axis establishment can lead to , a mirror-image arrangement of organs.

situs inversus

Inadequate caudal mesoderm production causes __ (caudal dysgenesis), characterized by fused lower limbs.

sirenomelia

Persistence of the primitive streak may produce a at the sacrococcygeal region.

sacrococcygeal teratoma

Mesenchymal cells that ingress through the primitive node and migrate cranially form the (prechordal mesoderm).

notochordal process

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

nucleus pulposus

The notochord induces overlying ectoderm to form the (neuroectoderm).

neural plate

Inhibition of BMP signaling by and from the notochord permits ectoderm to become neural tissue.

Noggin, Chordin

Elevation of neural plate edges produces the neural and a central neural .

folds, groove

Fusion of neural folds forms the neural tube, which initially remains open at two ends called __.

neuropores

The cranial (anterior) neuropore normally closes by day __ of development.

25

Failure of cranial neuropore closure between days 23–25 leads to __, absence of a major portion of the brain.

anencephaly

A skull defect with herniation of meninges and/or brain tissue due to cranial neuropore failure is called __.

encephalocele

Failure of the caudal neuropore to close between days 22–28 results in .

spina bifida

Neural crest cells originate at the border of the neural folds and migrate widely; they give rise to __ cells that secrete epinephrine in the adrenal medulla.

chromaffin

Melanocytes, Schwann cells, and craniofacial bones are all derivatives of the .

neural crest

Rapid growth of parietal mesoderm and ectoderm drives __ folding, creating the ventral body wall.

lateral

Rapid expansion of the forebrain produces __ folding, relocating the heart and diaphragm ventrally.

cephalocaudal

Paraxial mesoderm segments into paired blocks called __.

somites

The ventral part of a somite undergoes EMT to form __, precursor of vertebrae and ribs.

sclerotome

The dorsal epithelial portion of a somite is the __, which later splits into dermatome and myotome.

dermomyotome

Muscle precursors that remain near the neural tube form __ (back and intercostal) muscles.

primaxial

Myotome cells that cross the lateral somitic frontier (LSF) into parietal lateral plate mesoderm form __ muscles of limbs and body wall.

abaxial

The line separating somite from lateral plate mesoderm is the __ (LSF).

lateral somitic frontier

Lateral plate mesoderm splits into a dorsal (somatic) layer and a ventral (splanchnic) layer.

parietal, visceral

The parietal layer with ectoderm forms the __, which builds the ventral body wall.

somatopleure

The visceral layer with endoderm forms the __, which builds the gut wall.

splanchnopleure

Defects in the parietal lateral plate can produce __, an anterior abdominal wall opening with protruding intestines.

gastroschisis

Anterior paraxial mesoderm that does not segment forms the __ mesoderm, contributing to face and skull structures.

head

The surface ectoderm ultimately becomes the epidermis, while the __ gives rise to the CNS.

neuroectoderm