Embrology Weeks 3-5 and clinical correlates

Question 1

Gastrulation

Answer 1

Formation of the primitive node and streak at the caudal end of the epiblast.

Question 2

Trilaminar germ disc

Answer 2

Occurs right after primitive streak formation and is formed via hypoblast cells migrating thought the streak.

Makes the endo, excto and mesoderm

Question 3

Endoderm

Answer 3

Formed to replace the hypoblast cell layer and becomes the ventral layer of the trilaminar disc

Question 4

Mesoderm

Answer 4

Mesenchymal cells that dont form endoderm form mesoderm in the middle of the trilaminar disc

Question 5

Ectoderm

Answer 5

Formed from epiblast cells that dont become mesenchymal cells via migration. Is the dorsal layer of the trilaminar disc.

Question 6

Primordial germ cells

Answer 6

Originate from the epiblast and are the precursors for gametes

Question 7

Situs solitus

Answer 7

Normal left-right asymmetry

Question 8

Situs inversus

Answer 8

180 degree flip of normal right-left symmetry

Question 9

Situs ambiguous

Answer 9

Partial 180 degree flipped organs in left-right asymmetry

Question 10

Neurolation

Answer 10

Signals from the notochord causes ectoderm to thicken and from the neural plate.

Question 11

Two parts of the neural plate

Answer 11

Neural groove: forms along the midline of the neural plate

Neural folds: sides of neural plates that form the neural crest.

Question 12

Neural tube

Answer 12

Forms when the lateral edges of the folds come together. Gives rise to the CNS cells

Question 13

Spinal bifida

Answer 13

Incomplete formation of the neural tube.

Question 14

Neural crest cells

Answer 14

Detached cells migrate and give rise to PNS system, medula of the adrenal gland, melanocytes and facial bones

Question 15

Surface ectoderm forms what?

Answer 15

Epidermis of skin, appendages and nasal cavities. Also the anus cavity.

Question 16

Paraxial mesoderm forms what?

Answer 16

Cranial paraxial mesoderm: skeletal muscles, most cranium bones

Somatic paraxial mesoderm: produces dermatomes, myotome and sclerotomes.

Question 17

Intermediate mesoderm forms what?

Answer 17

Tissues of the urogential system and the cortex ofthe adrenal gland.

Question 18

Lateral plate mesoderm has what layers and produces what?

Answer 18

Splanchnic visceral mesoderm: smooth muscles, CT of the viscera and visceral linings of the thoracic organs. Also forms all heart layers and blood/lymph vessels

Somatic parietal mesoderm: serious epithelial layers of the thoracic region and fibrous pericardium

Question 19

Endoderm forms what?

Answer 19

Forms with the gut tube (which will form the Digestive system organs).

Produces epithelial lining of the GI tract, bladder and urethra and the trachea/bronchi of the lungs.

Question 20

Sarcococcygeal teratoma

Answer 20

Primitive streak does not disappear and causes tumors to form

• usually doesn’t kill fetus and can be safely excised

Question 21

Hydatiform moles

Answer 21

Degenerating chorionic villi from fetus death causes moles in the mother.

• can evolve into chriocarcinomas and give the mother cancer.

Question 22

Congenital diaphragmatic hernia (CDH)

Answer 22

Posterolateral defect in the formation of the diaphragm causes herniation of the intestines and stomach.

• this is caused by chromosal abnormalities and gene mutations to GATA6.
• usually compresses one lung and can cause pulmonary hypoplasia.

Question 23

Diaphragmatic eventration

Answer 23

Defective diaphragm musculature caused by failure of migration into the plueroperitoneal membrane diaphragm to balloon into the thoracic cavity

• creates diaphragmatic pouch

Question 24

Retro sternal herniations

Answer 24

Caused by intestinal herniation into the pericardial sac through the sternocostal hiatus