Embryology 3 - Gastrulation and Body Folding

Question 1

What is a Germ Layer? Where does it differentiate from?

Answer 1

• An embryonic tissue that forms in the 3rd week of embryogenesis
• Differentiates from the epiblast

Question 2

What are the 3 Types of Germ Layers?

Answer 2

• Ectoderm
• Endoderm
• Mesoderm

Question 3

What does the ectoderm give rise to?

Answer 3

Epithelium that makes contact with external environment, nerves.

Question 4

What does the endoderm give rise to?

Answer 4

Visceral epithelium, lungs

Question 5

What does the mesoderm give rise to?

Answer 5

Connective tissue, muscle, bone, blood

Question 6

What is Gastrulation?

Answer 6

The movement of cells through the primitive streak and into the interior of the embryo to form the 3 germ layers

Question 7

At gastrulation, epiblast cells undergo ____.

Answer 7

Epithelial-to-mesenchymal transition (EMT), enabling them to move to primitive streak and drop through it

Question 8

Direction of Movement of Gastrulating Cells

Answer 8

Cells move cranially and laterally as primitive streak retreats caudally (and embryonic disc grows caudally)

Question 9

What is Sacrococcygeal Teratoma?

Answer 9

Due to excessive gastrulation: germ layer formation continues past caudal end and excess germ layers becom tumor

Question 10

What is Caudal dysgenesis/Caudal regression syndrome/Sirenomelia?

Answer 10

Due to insufficient gastrulation: germ layer formation stopped prematurely

Insufficient mesoderm formed in caudal region of embryo

Question 11

What is the result of Cephalocaudal Folding?

Answer 11

Brings heart and septum transversum into the body, makes gut tube, thoracic cavity, and peritoneal cavity

Question 12

Cephalocaudal Folding is accomplished by what?

Answer 12

Cranial and caudal ends are folded under

Question 13

What are the components of Lateral Folding and how is it accomplished?

Answer 13

Left and right lateral plate mesoderm

Left and right plates are brought in toward the ventral body midline

Question 14

Amniotic sac membrane and yolk sac membrane are derived from ___.

Answer 14

Inner cell mass (ICM)

Question 15

Chorionic sac membrane is derived from ____.

Answer 15

Inner cell mass (ICM)

Question 16

What is Gastroschisis?

Answer 16

Intestines burst through abdominal wall

Lateral folds failed to fuse, weakness in ventral abdomina wall

Question 17

What is Ectopia Cardis?

Answer 17

Heart protrudes from thorax, sternum is split and spread apart, lung anomalies

Lateral folding failed to fuse in midline

Question 18

What is Omphalocele?

Answer 18

Intestines herniate into umbilical cord as normal part of intestine development but fail to return into peritoneal cavity

Question 19

What is Bladder Exstrophy?

Answer 19

Mucosa lining of urinary bladder “turned inside out” on surface of lower abdomen

Question 20

How does the neural crest form? What structures does it form?

Answer 20

• Day 20: fourth germ layer (neural crest) differentiates from the tip or crest of the neural folds
• Day 21: neural crest cells undergo EMT and migrate to other parts of the body
• Day 35: neural crest forms diverse structures: melanocytes, sympathetic and parasympathetic nervous systems, craniofacial bones and connective tissue, adrenal medulla, many others