Embryonic Period

Question 1

What is another name for the embryonic period?

Answer 1

The period of organogenesis.

Question 2

When does the embryonic period occur?

Answer 2

From the 3rd to the 8th week of development.

Question 3

What happens to the three germ layers during the embryonic period?

Answer 3

They give rise to specific tissues and organs.

Question 4

When do most birth defects occur?

Answer 4

During the embryonic period.

Question 5

By the end of the second month, what becomes recognizable?

Answer 5

The external body form and major organ systems.

Question 6

When does axis formation begin?

Answer 6

Late in the first week at the blastocyst stage.

Question 7

What causes disruption in axis formation?

Answer 7

Disruptions in cell signaling during cranial-caudal and left-right specification.

Question 8

What induces the ectoderm to form the neural plate?

Answer 8

The appearance of the notochord and prechordal mesoderm.

Question 9

What is the process of neural tube formation called?

Answer 9

Neurulation.

Question 10

List the sequence of structures formed during neurulation.

Answer 10

Primitive streak → primitive node → neural plate → neural groove → neural folds → neural tube.

Question 11

What cells separate from the neural tube during neurulation?

Answer 11

Neural crest cells.

Question 12

Which region of the ectodermal layer is broader?

Answer 12

The cephalic region.

Question 13

Which signaling pathway is upregulated in neural induction?

Answer 13

FGF (Fibroblast Growth Factor) signaling.

Question 14

Which molecule inhibits BMP4 during neural induction?

Answer 14

Chordin, noggin, and follistatin.

Question 15

What does BMP4 normally do?

Answer 15

It ventralizes ectoderm and mesoderm.

Question 16

What happens when BMP4 is inhibited?

Answer 16

Neuralization of ectoderm occurs.

Question 17

Which molecules are responsible for neural induction in the forebrain and midbrain?

Answer 17

Chordin, noggin, and follistatin.

Question 18

What induces the formation of hindbrain and spinal cord structures?

Answer 18

WNT3a and FGF.

Question 19

What regulates the cranial-caudal axis during neural induction?

Answer 19

Retinoic acid.

Question 20

What happens if BMP is not repressed?

Answer 20

Ectoderm forms epidermis, and mesoderm forms intermediate and lateral plate mesoderm.

Question 21

What is the default state of the ectoderm?

Answer 21

Neural tissue when protected from BMP exposure.

Question 22

What is neurulation?

Answer 22

The process by which the neural plate forms the neural tube.

Question 23

Which pathway regulates neurulation?

Answer 23

Planar cell polarity pathway.

Question 24

When does closure of the cranial neuropore occur?

Answer 24

On day 25.

Question 25

When does closure of the caudal neuropore occur?

Answer 25

On day 28.

Question 26

Where does fusion of neural folds begin?

Answer 26

In the cervical region (5th somite).

Question 27

What does the neural tube give rise to?

Answer 27

The central nervous system (CNS).

Question 28

What are the two main portions of the closed neural tube?

Answer 28

Caudal portion (spinal cord) and cephalic portion (brain vesicles).

Question 29

Where do neural crest cells originate?

Answer 29

At the lateral borders of the neuroectoderm.

Question 30

What process allows neural crest cells to migrate?

Answer 30

Epithelial-to-mesenchymal transition.

Question 31

What are the two migration pathways of neural crest cells?

Answer 31

Dorsal and ventral pathways.

Question 32

What does the dorsal pathway of neural crest cells form?

Answer 32

Melanocytes in the skin and hair follicles.

Question 33

What does the ventral pathway of neural crest cells form?

Answer 33

Sensory ganglia, sympathetic and enteric neurons, Schwann cells, and adrenal medulla.

Question 34

What structures do cranial neural crest cells form?

Answer 34

Craniofacial skeleton, cranial ganglia, glial cells, and melanocytes.

Question 35

What is another name for neural crest cells?

Answer 35

The fourth germ layer.

Question 36

Neural crest cells are involved in what percentage of birth defects?

Answer 36

One-third.

Question 37

Which cancers are associated with neural crest cells?

Answer 37

Melanoma and neuroblastoma.

Question 38

List five derivatives of neural crest cells.

Answer 38

Face and skull bones, cranial nerve ganglia, thyroid C cells, odontoblasts, dermis of face and neck.

Question 39

Which part of the nervous system do neural crest cells contribute to?

Answer 39

Peripheral nervous system (PNS).

Question 40

What do neural crest cells form in the adrenal gland?

Answer 40

Adrenal medulla.

Question 41

What do neural crest cells form in the heart?

Answer 41

Conotruncal septum.

Question 42

What determines the fate of the ectodermal germ layer?

Answer 42

BMP concentration.

Question 43

Which transcription factors specify neural crest cells?

Answer 43

SNAIL and FOXD3.

Question 44

Which transcription factor promotes neural crest migration?

Answer 44

SLUG.

Question 45

What do intermediate BMP concentrations induce?

Answer 45

Neural crest formation.

Question 46

What structures do otic placodes form?

Answer 46

Otic vesicles, which develop into hearing and equilibrium structures.

Question 47

When do lens placodes appear?

Answer 47

During the 5th week of development.

Question 48

What do lens placodes form?

Answer 48

The lenses of the eyes.

Question 49

What is anencephaly?

Answer 49

Failure of cranial neural tube closure resulting in absence of most brain and skull.

Question 50

What is spina bifida?

Answer 50

Failure of neural tube closure from cervical to caudal regions.

Question 51

Where is spina bifida most common?

Answer 51

In the lumbosacral region.

Question 52

Which gene mutation is associated with neural tube closure defects?

Answer 52

VANGL gene mutation.

Question 53

How can neural tube defects be prevented?

Answer 53

By taking 400 µg of folic acid daily starting 3 months before conception.

Question 54

When does paraxial mesoderm form?

Answer 54

On the 17th day of development.

Question 55

What are the three regions of mesoderm?

Answer 55

Paraxial, intermediate, and lateral plate mesoderm.

Question 56

What does the lateral plate mesoderm form?

Answer 56

Somatic and splanchnic layers.

Question 57

What cavity is formed by the lateral plate mesoderm?

Answer 57

Intraembryonic cavity.

Question 58

When do somites first appear?

Answer 58

On day 20 in the occipital region.

Question 59

How many pairs of somites form by week 5?

Answer 59

42 to 44 pairs.

Question 60

What do somites form in the embryo?

Answer 60

The axial skeleton.

Question 61

Which signaling pathway regulates somite segmentation?

Answer 61

Notch and WNT pathways.

Question 62

What regulates somite boundary formation?

Answer 62

Retinoic acid, FGF8, and WNT3a.

Question 63

What does the sclerotome form?

Answer 63

Vertebrae, ribs, and tendons.

Question 64

What does the myotome form?

Answer 64

Skeletal muscles.

Question 65

What does the dermatome form?

Answer 65

Dermis of the skin.

Question 66

Which protein induces sclerotome differentiation?

Answer 66

Sonic Hedgehog (SHH).

Question 67

Which gene marks dermomyotome regions?

Answer 67

PAX3.

Question 68

Which gene is expressed in dorsomedial muscle precursors?

Answer 68

MYF5.

Question 69

Which gene is expressed in dorsolateral muscle precursors?

Answer 69

MYOD.

Question 70

What signal induces dermis formation?

Answer 70

Neurotrophin 3 (NT3).

Question 71

What does the intermediate mesoderm form?

Answer 71

Urogenital structures such as kidneys and gonads.

Question 72

What are nephrotomes?

Answer 72

Segmented clusters of intermediate mesoderm forming early kidney structures.

Question 73

What is the nephrogenic cord?

Answer 73

Unsegmented mass of tissue forming lower kidney structures.

Question 74

What does the parietal layer of lateral plate mesoderm form?

Answer 74

Dermis, bones, connective tissue, and muscles of the body wall and limbs.

Question 75

What does the visceral layer of lateral plate mesoderm form?

Answer 75

The wall of the gut tube with the endoderm and serous membranes.

Question 76

What forms the intraembryonic cavity?

Answer 76

The space between the parietal and visceral layers of lateral plate mesoderm.

Question 77

What are the two main processes of blood vessel formation?

Answer 77

Vasculogenesis and angiogenesis.

Question 78

What growth factor induces blood island formation?

Answer 78

FGF2 (Fibroblast Growth Factor 2).

Question 79

What factor directs hemangioblast differentiation?

Answer 79

VEGF (Vascular Endothelial Growth Factor).

Question 80

What region produces hematopoietic stem cells?

Answer 80

Aorta-gonad-mesonephros (AGM) region.

Question 81

Which organ is the main site of hematopoiesis from 2 to 7 months?

Answer 81

The liver.

Question 82

After 7 months, what becomes the main site of blood formation?

Answer 82

Bone marrow.

Question 83

Which signaling molecule induces VEGF expression in arterial development?

Answer 83

Sonic Hedgehog (SHH).

Question 84

Which molecule is crucial for arterial development?

Answer 84

EPHRINB2 via the NOTCH pathway.

Question 85

Which transcription factor regulates lymphatic vessel differentiation?

Answer 85

PROX1.

Question 86

What is a capillary hemangioma?

Answer 86

A dense collection of capillary vessels, common in infancy.

Question 87

How common are capillary hemangiomas?

Answer 87

Occur in about 10% of births.

Question 88

Where do capillary hemangiomas often occur?

Answer 88

In the craniofacial region.

Question 89

Which growth factor is elevated in hemangiomas?

Answer 89

Insulin-like Growth Factor 2 (IGF2).

Question 90

What is the main organ system derived from the endoderm?

Answer 90

The gastrointestinal tract.

Question 91

What surfaces does the endoderm cover early in development?

Answer 91

The ventral surface of the embryo and the roof of the yolk sac.

Question 92

What structures does the endoderm form?

Answer 92

Lining of gut, respiratory tract, urinary bladder, ureter, tympanic cavity, and auditory tube.

Question 93

What organs develop from endodermal parenchyma?

Answer 93

Thyroid, parathyroid, liver, and pancreas.

Question 94

What immune structures derive from endoderm?

Answer 94

Reticular stroma of the thymus and tonsils.

Question 95

What cells migrate from the endoderm to form gametes?

Answer 95

Germ cells from the posterior wall.

Question 96

What can failure of lateral body wall closure cause?

Answer 96

Ventral body wall defects.

Question 97

Which membrane separates the mouth from the gut early on?

Answer 97

Oropharyngeal membrane.

Question 98

When does the oropharyngeal membrane rupture?

Answer 98

During the 4th week.

Question 99

What connects the midgut to the yolk sac?

Answer 99

Vitelline duct.

Question 100

What is the function of the yolk sac?

Answer 100

Provides nutrients and forms the first blood cells.

Question 101

What separates the hindgut from the proctodeum?

Answer 101

Cloacal membrane.

Question 102

When does the cloacal membrane break down to form the anus?

Answer 102

During the 7th week.