Embryology

Question 1

Two germ layer stage

Answer 1

Inner cell mass splits into epiblast, hypoblast

Epiblast folds, becomes amniotic cavity

Bilaminar disc

Question 2

Function of the hypoblast

Answer 2

Supports embryo

Question 3

Function of the epiblast

Answer 3

Becomes embryo

Question 4

What occurs during gastrulation?

Answer 4

Primitive streak forms

Primitive streak invaginates to form primitive groove

Question 5

What is the primitive streak?

Answer 5

Line of thickened cells on the upper surface of bilaminar disc

Becomes primitive groove

Question 6

Function of primitive groove

Answer 6

Epiblast cells migrate through it, form germ layers

Question 7

What do the first cells to migrate through primitive groove become?

Answer 7

Endoderm

Question 8

What do the second cells to migrate through primitive groove become?

Answer 8

Mesoderm

Question 9

What do the cells that don’t migrate through the primitive groove become?

Answer 9

Ectoderm

Question 10

What determines what different germ cells differentiate into?

Answer 10

Where they migrated through the primitive groove

When they migrated through the primitive groove

Question 11

What is the coelom?

Answer 11

Hollow space around viscera

Lined with mesoderm

Question 12

How is the coelom formed?
1)
2)
3)

Answer 12

1) Lateral mesoderm splits into splanchnic, somatic mesoderm
2) Yolk sac ‘purse strings’ from embryo
3) Coelom forms between splanchnic and somatic mesooderm

Question 13

What does the ectoderm become?

Answer 13

Skin, nervous system

Question 14

Neural tube formation
1)
2)
3)

Answer 14

1) Notochord induces overlying ectoderm to form neural plate
2) Neural plate folds to become neural groove
3) Neural groove folds to form neural tube

Question 15

What does the neural crest form?

Answer 15

PNS

Some non-neural structures (face)

Question 16

Neural crest formation

Answer 16

Cells overlying neural tube are induced to form neural crest

Question 17

What forms the brain?

Answer 17

Rostral end of neural tube (hox-gene mediated)

Forms vesicles

Question 18

CNS formation

Answer 18

Rostral neural tube forms vesicles. Vesicles become brain

Unvesiculated neural tube becomes spinal cord

Question 19

What are the divisions of the mesoderm?
1)
2)
3)
4)

Answer 19

1) Paraxial mesoderm
2) Intermediate mesoderm
3) Lateral mesoderm
4) Extraembryonic

Question 20

What does the paraxial mesoderm form?

Answer 20

Dermis
Axial skeleton
Axial muscles
Limb muscles

Question 21

What does the intermediate mesoderm form?

Answer 21

Urogenital tract

Question 22

What does the lateral mesoderm form?

Answer 22

Ventrolateral body wall
Visceral pleura 
Peritoneum
Pericardium
Blood vessels
Blood-forming tissue
Heart 
Wall of gut
Respiratory tissues

Question 23

What does the extraembryonic mesoderm form?

Answer 23

Life-support structures

Question 24

Which part of the mesoderm swells to form somites?

Answer 24

Paraxial

Question 25

What does the paraxial mesoderm swell to form?

Answer 25

Somites

Question 26

``` Somite formation 1) 2) 3) 4) ```

Answer 26

1) Paraxial mesoderm swells to form somitomeres along its axis 2) Once 20 somitomeres present, 8th somitomere becomes a somite 3) Somitomeres become independent somites from 8th caudally 4) Somitomeres 1-7 never become separate, become head

Question 27

Somite development

Answer 27

Somites split into: 1) Sclerotome and dermomyotome 2) Dermomyotome splits into dermatome, myotome

Question 28

What does the sclerotome form?

Answer 28

Skeleton, except skull

Question 29

What does the myotome become?

Answer 29

Trunk muscles

Question 30

What does the dermotome become?

Answer 30

Dermis of skin | Supports epithelium, formed by ectoderm

Question 31

What does the endoderm form?

Answer 31

All derivatives are epithelial tissues Line mesoderm structures to form organs

Question 32

Neural crest non-neural derivatives

Answer 32

Melanocytes Schwann cells Bone, muscle, cartilage of jaw Dentine

Question 33

Mouth, anus development

Answer 33

1) Under three weeks - Proctodeum, stomadeum 2) Three weeks - Oral plate breaks, oral cavity formed 3) Six weeks - Hind gut and allantois join to form cloaca. No distinction between anus and genitals 4) Eight weeks - Urorectal septum divides rectum form urogenital tract

Question 34

What are the proctodeum and stomadeum?

Answer 34

Anus, mouth pits. | Under three weeks of development

Question 35

What is the oral plate?

Answer 35

Separates stomadeum and foregut. | Breaks at three weeks of development

Question 36

Which germ layers form cloacal membrane?

Answer 36

Ectoderm and endoderm

Question 37

What is the allantois?

Answer 37

Branch of the hind gut LIes in the body stalk Becomes bladder and urethra Stores nitrogenous waste in some animals. Vestigial in humans

Question 38

Which germ layer is the urorectal septum derived from?

Answer 38

Mesoderm

Question 39

Which germ layer forms the urogenital system?

Answer 39

Intermediate mesoderm (apart from bladder and urethra)

Question 40

How does the bladder form?

Answer 40

Around nine weeks of development. | Allantois swells

Question 41

What are the three stages of kidney development?

Answer 41

Pronephros Mesonephric duct Metanephros

Question 42

``` Kidney development 1) 2) 3) 4) 5) 6) ```

Answer 42

1) Pronephros forms nephrosomes, pronephric duct. 2) Nephrosomes degenerate. Pronephric duct becomes mesonephric duct 3) Mesonephric duct radiates mesonephric tubules. Mesonephric tubules degenerate. 4) Mesonephric duct induces formation of metanephros 5) Ureters bud from mesonephros at the bladder. Kidneys form form the metanephros inferiorly, migrate superiorly 6) Mesonephric duct joins gonads, becomes vas deferens in males

Question 43

Mullerian duct

Answer 43

Paramesonephric duct Becomes Fallopian tubes, uterus in females Degenerates in males

Question 44

How do viscera form?

Answer 44

Outpocketings of endoderm interact with mesoderm

Question 45

Which viscera form as outpocketings of the endoderm?

Answer 45

Trachaea, lungs, liver pancreas

Question 46

What happens to the heart at day 20 of development?

Answer 46

Bilateral endocardial cells fuse in coelom formation

Question 47

Which germ layer forms the myocardium, endocardium, pericardium?

Answer 47

Mesoderm

Question 48

Which parts of the heart are mesodermally-derived?

Answer 48

Myocardium, pericardium, endocardium

Question 49

How does the aortic arch develop?

Answer 49

1) Initially a symmetrical, segmented structure that resembles gills 2) Vessels selectively lost

Question 50

GIT formation

Answer 50

1) At one month, foregut and hindgut, midgut connected to the yolk sac 2) Gut twists in midgut around axis of yolk stalk, superior mesenteric artery 3) Gut continues to grow, gives shape of intestines (large surrounding small) 4) Week six/seven - Gut grows too large for body. Herniates into body stalk 5) Week nine - Body cavity larger, gut retracts back

Question 51

At which week of development does the gut herniate into the body stalk?

Answer 51

Week six/seven

Question 52

At which week of development does the gut retract back into the body cavity?

Answer 52

Week nine

Question 53

What is omphalocele?

Answer 53

Gut fails to retract into body cavity in week nine

Question 54

What is umbilical hernia?

Answer 54

Gut retracts back into body cavity, but no sealing of abdominal wall

Question 55

What is it called when the gut retracts back into the body cavity, but the abdominal wall doesn't seal?

Answer 55

Umbilical hernia