Embryology

Question 1

2 differences of chick gastrulation vs. frog (other than being flat)

Answer 1

1. endoderm displaces hypoblast

2. Hensen’s node closes primitive streak to end gastrulation

Question 2

What does the blastocoel form in the adult?

Answer 2

Nothing (gets filled up)

Question 3

Compare blastula cells in mesolecithal

Answer 3

Asymmetric/different because yolk slows cleavage

Question 4

Describe steps of neurulation

Answer 4

Thick dorsal ectoderm = neural plate
Invaginates, neural groove w/folds on sides
Folds fuse, enclosing neural tube
Epidermal ectoderm grows over top

Question 5

Germ layer origin of chorion

Answer 5

Ectoderm, somatic hypomere mesoderm

Question 6

Name the 4 major extra-embryonic membranes

Answer 6

1. Yolk sac
2. Amnion
3. Chorion
4. Allantois

Question 7

Blastula formation events

Answer 7

Form hollow ball of cells; hole = blastocoel

Question 8

Which organisms have a chorioallantoic placenta?

Answer 8

Most eutherian mammals

Question 9

Morula (def)

Answer 9

symmetric ball of cells

Question 10

Germ layer origin of allantois

Answer 10

Endoderm, splanchnic hypomere mesoderm (from hindgut region)

Question 11

Events of cleavage

Answer 11

Short/no growth phase between cell divisions (division while overall embryo maintains size)

Question 12

Major events of organogenesis

Answer 12

• embryo grows, lengthens

- germ layers further differentiate, work in concert to form complex organs

Question 13

Which direction does Koller’s sickle move?

Answer 13

posterior to anterior

Question 14

How do extra-embryonic membranes form?

Answer 14

Lateral germ layers (ectoderm, hypomere mesoderm, endoderm) form folds, grow around embryo

Question 15

Describe blastodisk of macrolecithal egg from dorsal to ventral

Answer 15

epiblast (dorsal, formed first, forms embryo), blastocoel (middle), hypoblast (ventral, forms after, guides cell migration in gastrulation)

Question 16

Where do neural crest cells originate?

Answer 16

In neural folds (during neurulation)

Question 17

Animal pole (def)

Answer 17

thinner, yolk-less end of blastula/gastrula (top in most diagrams, made of ectoderm)

Question 18

Germ layer origin of notochord?

Answer 18

Mesoderm

Question 19

Homoplasty (def)

Answer 19

Structures with a similar appearance

Question 20

What does the archenteron become in the adult?

Answer 20

Gut (blastopore = anus in deuterostomes)

Question 21

What does the posterior marginal zone in the chick embryo become?

Answer 21

Koller’s sickle, then primitive streak

Question 22

Shape of macrolecithal-egg embryo

Answer 22

disk

Question 23

What does the neural tube become in adults?

Answer 23

Brain: ventricles

Spinal cord: cerebrospinal fluid canal

Question 24

Function of the yolk sac

Answer 24

extra-embryonic membrane surrounding yolk, forming vitelline vessels to transport nutrients from yolk to embryo

Question 25

Which vertebrates have a yolk sac placenta?

Answer 25

Most methatherian mammals

Question 26

Function of allantois/allantoic membrane

Answer 26

Sequester nitrogenous wastes away from the embryo so it doesn't poison itself

Question 27

Describe epiblast from anterior to posterior

Answer 27

Area opaca -> area pellucida (most of the epiblast) -> posterior marginal zone (thicker, becomes Koller's sickle, then primitive streak)

Question 28

What does the coelomic fold become in the adult?

Answer 28

Muscular diaphragm (mammals only)

Question 29

Mesoderm differentiates into...

Answer 29

Notochord, Epimere, Mesomere, Hypomere

Question 30

What happens to the hypoblast in the chick embryo?

Answer 30

Displaced by endoderm during gastrulation | Hypoblast: lower layer of blastula, directly dorsal to yolk

Question 31

Cells migrate into the blastopore through which analogous structures in the frog and chick embryo?

Answer 31

frog: blastopore chick: primitive streak

Question 32

What does the coelom divide into in all vertebrates? What separates them?

Answer 32

Pericardial & pleuroperitoneal cavities; transverse septum

Question 33

Vegetal pole (def)

Answer 33

Thicker, yolk-filled end of blastula/gastrula (bottom in most diagrams, made of endoderm)

Question 34

Which direction does Hensen's node move?

Answer 34

anterior to posterior

Question 35

How do metatherian mammals form the embryonic placenta?

Answer 35

From yolk sac

Question 36

What is Hensen's node?

Answer 36

Anterior end of the primitive streak

Question 37

Germ layer origin of yolk sac

Answer 37

Endoderm, splanchnic hypomere mesoderm

Question 38

How do complex organs form in the embryo?

Answer 38

Several germ layers work together

Question 39

Which organisms do/don't have an allantois & why?

Answer 39

Anamniotes: no, wastes diffuse into water Mammals: no, wastes removed by placenta Sauropsids: yes, can't get rid of wastes

Question 40

Germ layer origin of amnion

Answer 40

Ectoderm, somatic hypomere mesoderm

Question 41

Ectoderm differentiates into...

Answer 41

Neural crest cells, neural plate cells, Epidermal

Question 42

Epimere mesoderm forms... In the 24-hour chick embryo (overall structure name, plus differentiated layers)

Answer 42

somites (little balls); dermatome, myotome, sclerotome

Question 43

What does the pleuroperitoneal cavity divide into in mammals, and what separates it?

Answer 43

Pleural cavity, peritoneal cavity; coelomic fold (becomes muscular -> diaphragm)

Question 44

What is contained in the amnion?

Answer 44

Embryo, amniotic fluid

Question 45

Who has protostome development?

Answer 45

Invertebrates: arthropods, molluscs, insects, etc.

Question 46

How do eutherian mammals form the placenta?

Answer 46

From chorioallantoic membrane

Question 47

3 main events of gastrulation

Answer 47

1. archenteron formation by cell migration into blastocoel 2. germ layer differentiation 3. committed anterior/posterior

Question 48

Function of amnion

Answer 48

Cushion embryo in amniotic fluid, prevent dessication (b/c waterproof)

Question 49

What is the transverse septum & what does it do?

Answer 49

Fold that divides coelom into pericardial & pleuroperitoneal cavities

Question 50

Function of placenta

Answer 50

Exchange gases, nutrients, wastes between mother & embryo

Question 51

Where is the coelom located?

Answer 51

Between the somatic and splanchnic hypomere mesoderm

Question 52

3 differences between deuterostomes & protostomes

Answer 52

1. Cleavage pattern (spiral in protostomes, radial in deuterostomes) 2. End function of blastopore (mouth in protostomes, anus in deuterostomes) 3. Origin of skeleton (protostomes: ectoderm mostly, deuterostomes: mesoderm mostly)

Question 53

How is the primitive streak formed?

Answer 53

Migration of Koller's sickle from posterior to anterior (mnemonic: sickle cuts up to form streak)

Question 54

Describe structure & function of chorion

Answer 54

Membrane fuses w/allantois to form chorioallantoic membrane; allows gas exchange through egg shell via many blood vessels

Question 55

What is the coelomic fold and what does it do?

Answer 55

Divides pleuroperitoneal cavity in mammals into pleural and peritoneal cavities by fusing with transverse septum