Embryology 3

Question 1

In what developmental phase do the 3 germ layers arise?

Answer 1

gastrulation

Question 2

What are the 3 germ layers?

Answer 2

ectoderm, mesoderm, ectoderm

Question 3

What is the first event of gastrulation?

Answer 3

formation of primitive streak

Question 4

What is the primitive streak?

Answer 4

thickened midline of embryonic disc that results from epiblast cell thickening

Question 5

What is the significance of the primitive streak in terms of axial positioning?

Answer 5

the primitive streak defines the caudal end of the embryo

Question 6

What structure is contained within the primitive streak?

Answer 6

primitive groove

Question 7

Describe how the endoderm is formed.

Answer 7

first wave of proliferating epiblast cells invade the hypoblast and eventually replace the hypoblast cells

Question 8

Describe how the intraembryonic mesoderm is formed.

Answer 8

second wave of proliferating epiblast cells invade space between epiblast and newly-formed endoderm

Question 9

Describe how the ectoderm is formed.

Answer 9

epiblast cells that don’t form the endoderm or intraembryonic mesoderm then make up the ectoderm

Question 10

The ectoderm faces what embryonic structure?

Answer 10

as the ectoderm is the dorsal-most layer, it faces the amniotic cavity

Question 11

When does sacrococcygeal teratoma happen?

Answer 11

when the primitive streak doesn’t completely degenerate

Question 12

What are the features of sacrococcygeal teratoma? (3)

Answer 12

germ cell tumor that contains tissues derived from all 3 layers at different stages of differentiation; benign; protrude from anal area

Question 13

The surface ectoderm gives rise to (6)

Answer 13

epidermis of skin/hair/nails; mammary glands; anterior pituitary gland; enamel of teeth; inner ear; lens of eye

Question 14

The neuroectoderm gives rise to (2)

Answer 14

neural crest; neural tube

Question 15

The neural crest gives rise to (6)

Answer 15

dorsal root ganglia; cranial ganglia/nerves; sensory ganglia/nerves; adrenal medulla; melanocytes; some bones of skull

Question 16

The neural tube gives rise to (4)

Answer 16

central nervous system; retina; pineal body; posterior pituitary

Question 17

The ectoderm gives rise to (2)

Answer 17

surface ectoderm; neuroectoderm

Question 18

The mesoderm gives rise to (4)

Answer 18

head; paraxial; intermediate; lateral

Question 19

The head gives rise to (3)

Answer 19

skull; head muscles/connective tissue; dentine of teeth

Question 20

The paraxial gives rise to (4)

Answer 20

trunk/limb muscles; bones of axial skeleton; dermis of skin; connective tissue of body wall

Question 21

The intermediate gives rise to (3)

Answer 21

urinary tract; gonads and gonadal ducts; accessory glands of gonads

Question 22

The lateral gives rise to (6)

Answer 22

cardio system; spleen/lymphatic system; adrenal cortex; pleural/pericardial/peritoneal membranes; muscles/connective tissue of viscera; bones of appendicular skeleton

Question 23

The endoderm gives rise to (3)

Answer 23

epithelium of gut; epithelium of respiratory tract; epithelial parts of glands

Question 24

The epithelium of the respiratory tract gives rise to (3)

Answer 24

epithelia of trachea; bronchi; pulmonary vessels

Question 25

The epithelium of glands gives rise to (3)

Answer 25

epithelia of para/thyroid gland; tonsils; auditory tube

Question 26

How does the allantois arise?

Answer 26

as an outpouching of the yolk sac into the connecting stalk

Question 27

What is the function of the allantois?

Answer 27

allows gas exchange and acts as reservoir for urine during embryonic life

Question 28

The blood vessels of the allantois ultimately become

Answer 28

umbilical arteries and veins

Question 29

What is the ultimate fate of the allantois?

Answer 29

as bladder develops, allantois regresses to become urachus and eventually the median umbilical ligament in adults

Question 30

What structure marks the site of the future mouth?

Answer 30

prechordal plate

Question 31

What structure marks the site of the future anus?

Answer 31

cloacal membrane

Question 32

Where does the notochordal process start to develop?

Answer 32

forms at cranial end of primitive streak

Question 33

How does the notochord form?

Answer 33

notochordal process ---> notochordal plate ---> notochord

Question 34

What is the function of the notochord? (2)

Answer 34

provides rigidity to embryo; defines future site of vertebral column

Question 35

How does the notochord further develop?

Answer 35

segments of it can form the nucleus pulposus of intervertebral discs

Question 36

Why is the notochord critical to embryonic development?

Answer 36

because once it is formed, it releases signaling factors that induce neurulation

Question 37

How does the neural tube form?

Answer 37

invaginations of the neural plate (formed by notochordal process) form neural folds, which fuse together

Question 38

The neural canal develops into (2)

Answer 38

cerebral ventricles; spinal canal

Question 39

The openings of the neural tube are called

Answer 39

cranial and caudal neuropores

Question 40

Where are neural crest cells located?

Answer 40

in a layer between the surface ectoderm and neural tube

Question 41

What is the basis for the onset of neural tube defects?

Answer 41

defects occur when the neuropores don't close

Question 42

What is anencephaly?

Answer 42

faire of cranial neuropore to close, which results in abnormal brain/skull development and is not compatible with life

Question 43

What is spina bifida?

Answer 43

failure of caudal neuropore to close, which results in defects of the spinal cord and/or vertebral column

Question 44

Where does the mesoderm proliferate following its formation during gastrulation?

Answer 44

proliferates on each side of neural plate

Question 45

What are somites?

Answer 45

tissue blocks

Question 46

Where do somites begin to form?

Answer 46

cranially — formation extends caudally

Question 47

How does the intraembryonic coelom form?

Answer 47

when spaces in the lateral mesoderm appear and then coalesce

Question 48

How does the intraembryonic coelom affect the lateral mesoderm?

Answer 48

dividies the lateral mesoderm into two layers: parietal/somatic layer + visceral/splanchnic layer

Question 49

What are the two layers of the lateral mesoderm and where do they attach?

Answer 49

parietal/somatic layer (attaches to ectoderm) + visceral/splanchnic layer (attaches to endoderm)

Question 50

What is the ultimate fate of the intraembryonic coelom?

Answer 50

coalesces with the extraembryonic coelom but eventually develops into the cavities of the body (pleural, pericardial, abdominal)

Question 51

Where is the intermediate mesoderm located?

Answer 51

between paraxial and lateral mesoderm

Question 52

What is the ultimate fate of the intermediate mesoderm?

Answer 52

tissue will eventually develop into the urogenital tract

Question 53

In embryonic folding, what folds initially develop?

Answer 53

3 — cranial fold, caudal fold, lateral body fold

Question 54

Describe the steps of the head fold.

Answer 54

rapid growth of neural folds brings oropharyngeal membrane (+ structures cranial to it) ventrally, causing them to lie ventral and caudal to the cranial neural folds

Question 55

Describe the steps of the tail fold.

Answer 55

rapid growth of caudal end of neural folds causes tail fold, which brings cloacal membrane ventral to the caudal ends of primitive streak and neural folds

Question 56

Describe how the allantois changes position during the tail fold.

Answer 56

allantois, initially caudal to cloacal membrane, is brought ventrally by tail fold into position cranial to cloacal membrane

Question 57

Why are the lateral folds important?

Answer 57

they define the body walls

Question 58

The result of the lateral folds is often called

Answer 58

"a tube in a tube"

Question 59

How is the abdominal cavity formed?

Answer 59

formed during lateral fold, when the intraembryonic coelom is pinched off

Question 60

How is the gut tube formed?

Answer 60

formed during lateral fold, when the yolk sac is pinched off

Question 61

The lateral fold causes what change to the amniotic cavity with respect to the entire embryo?

Answer 61

causes the amniotic cavity to surround the entire embryo

Question 62

All lateral folds meet at what area?

Answer 62

meet at the umbilicus, which is the ventral midline of the embryo

Question 63

After lateral folding is completed, what structures become incorporated into the umbilical cord? (3)

Answer 63

remnants of yolk sac; connecting stalk; allantois