Process of Embryonic Development

Question 1

What are the four major steps of embryogenesis?

Answer 1

1. Cleavage
2. Gastrulation
3. Organogenesis
4. Gametogenesis

Question 2

What is the hallmark of mammalian cleavage?

Answer 2

Blastocyst

Question 3

What are the three germ layers formed during gastrulation?

Answer 3

1. Ectoderm (outer layer)
2. Endoderm (inner layer)
3. Mesoderm (middle layer)

Question 4

What tissues/organs do each germ layer give rise to?

Answer 4

Mesoderm - cells of epidermis and nervous system
Endoderm - lining of digestive tube and associated organs, pancreas, liver etc
Mesoderm - several organs (heart, kidney, gonads), connective tissue (muscle, bone, tendons), and blood cells

Question 5

What type of cells form the neural tube in neurulation?

Answer 5

Mid-dorsal ectodermal cells

Question 6

What does the ectoderm give rise to in neurulation?

Answer 6

1. Neural tube; forms brain and spinal cord
2. Externally positioned epidermis of skin
3. Neural crest cells which migrate and form peripheral neurons, glia, pigment cells of skin, and other cell types

Question 7

What defects can occur due to improper neural tube closure?

Answer 7

• Anencephaly - forebrain remains in contact with amniotic fluid and degenerates
• Spina Bifida - due to defect in posterior closure