HB 2.1 - Intro To Embryology

Question 1

Define “Blastocyst”

Answer 1

• Day 4-5 after fertilisation

- Contains blastocoel, trophoblast and inner cell mass

Question 2

Define “Trophoblast”

Answer 2

• Day 4-5 after fertilisation
• The outermost layer of blastocyst after its hatching from the zona pellucida
• Extraembryonic: later forms cytothrophoblast and synctothrophoblast (involved in forming placenta and invasion of uterine lining)

Question 3

Define “Inner Cell Mass”

Answer 3

• Also called “Embryoblast”

- Able to differentiate into all body cell types

Question 4

Define “Morphogen”

Answer 4

• Diffusible molecule that acts as a signalling molecule through a concentration gradient which influences cell differentiation and migration

Question 5

Define “Transcription Factor”

Answer 5

• Proteins that bind to specific element in DNA to turn on/off downstream genes

Question 6

Describe the process of Gastrulation

Answer 6

• The process of turning bilaminar into trilaminar
• Epiblast cells migrate through primitive streak:
  i. Cells replacing the ventral hypoblast = Endoderm
  ii. Cells in the middle = Mesoderm
  iii. Cells at the dorsal side = Ectoderm

Question 7

Describe the process of Neurulation

Answer 7

• The development of early nervous system

1) Mesodermal notochord signals the immediate dorsal ectoderm to become neuroectoderm
2) Neuroectoderm invaginates
3) Forming of neural grove and neural fold
4) Causes the folding of neural plate
5) Forms neural tube (precursor of CNS)

Question 8

Describe the process of Body Folding

Answer 8

• Converting a 2D germ disc into 3D through x3 types of flexion at the same time

i. Rostral (head) folding
1) Forebrain overgrows the cranial structures
2) Forces a 180º rotation -> Brings cranial structures (eg. mouth, primitive heart) caudal

ii. Caudal (tail) folding
1) Caudal neural tube outgrows the rest of body
2) Forces 180º rotation -> Brings caudal structures (eg. cloaca, hindgut) rostral
3) Umbilical connecting stalk relocates next to yolk sac

iii. Bilateral Folding
1) Dorsoventral splitting of mesoderm (dorsal mesoderm following ectoderm; ventral mesoderm following endoderm)
2) Mesoderm layers wrap around the embryo -> Medial movement for structures (eg. aortae)
3) Ventral mesoderm encloses and seals off gut tube except at opening of umbilical cord

Question 9

Describe the fate of Ectoderm

Answer 9

• Epidermis

- Nervous Tissue

Question 10

Describe the fate of Endoderm

Answer 10

• Dermis
• Connective Tissue (Muscle, Bones, Cartilage, Circulatory System)
• Limbs
• Kidneys
• Gonads

Question 11

Describe the fate of Mesoderm

Answer 11

• Gastrointestinal Tract

- GI derivatives (eg. Lungs)