Embryology and Development 2

Question 1

name the sections of bilaminar embryonic disk

Answer 1

top layer: EPIBLAST (will become embryo)
bottom layer: HYPOBLAST (forms extra-embryonic tissues)

Question 2

name layers above and below bilaminar embryonic disk

Answer 2

above
- amniotic cavity
- amniotic sac (aka amnion)

below
- yolk sac

Question 3

name components of embryonic disk (top to bottom)

Answer 3

(all contained by blastocele)

Amniotic cavity (surrounded by amniotic sac)

form after implantation
Embryonic disk
- Epiblast: 3 germ layers
- Hypoblast: forms extra-embryonic tissues)

Question 4

Name of the cavity on the inside of the blastocyst

Answer 4

blastocele

Question 5

Name the 3 germ layers that make up the embryonic disk top to bottom

Answer 5

ectoderm (don’t migrate through primitive streak): forms skin, nervous system
mesoderm: forms blood, muscle, bones
endoderm: forms organs

Question 6

what is gastrulation and when does it occur

Answer 6

day 13-14
differentiation of epiblast layer into different tissue types

Question 7

explain process of gastrulation

Answer 7

differentiation of epiblast into 3 tissue types
1. epiblast layer elongates (why? humans are long)
2. PRIMITIVE STREAK forms in epiblast (creates thick section of epiblast)
- end closest to primitive streak is tail (caudal), farthest is the head (cephalic)

Question 8

What’s the difference between the hypoblast and endoderm cells?

Answer 8

endoderm cells form in place of hypoblast cells during gastrulation and push them away to line the yolk sac

Question 9

What is the notochord? what is it made of? where is it located? when does it form?

Answer 9

• solid cylinder of cells under ectoderm
• made of mesodermal cells
• forms day 16
• uses INDUCTION to chemically signal ectoderm to form the NEURAL PLATE (day 18)

Question 10

features of ectoderm around day 18 (cephalic to caudal direction)

Answer 10

• OROPHARYNGEAL membrane (thin)
  will become mouth
• Neural plate (thick)
• primitive streak
• CLOACAL membrane (thin)
  will become anus

Question 11

explain formation of the neural tube

Answer 11

after induction (notochord stimulated neural plate formation)
1. neural plate starts to fold. creates neural groove with neural fold on either side (a lil squiggle!)
2. groove becomes deeper, crests higher,
3. crests get closer together, some pieces come off -> neural crest cells
4. crests join, NEURAL TUBE formed

*folding starts in middle with caudal and cephalic ends the last to fold

Question 12

functions of neural tube and neural crest

Answer 12

tube: forms brain and spinal cord
crest: sensory and post-ganglionic portion of PNS, general connective tissue of the head

Question 13

somites

Answer 13

• form alongside neural tube in mesoderm
• form vertebral column, ribcage and and some other bones

Question 14

notochord

Answer 14

structure in mesoderm that signals induction to form neural plate