embryogenesis

Question 1

why is developmental biology important?

Answer 1

-phenotypic differences are encoded in our genes

Question 2

What are two main periods of human development?

Answer 2

1. embryonic period:
   - up to the ends of week 8
   - most of organogenesis occurs in these 8 weeks
2. Fetal period
   - the remaining time in utero
   - involves growth and modeling

Question 3

outline the mechanisms of development from embryo to adult.

Answer 3

1. fertilasation
2. cleavage
3. gastrulation
4. neurulation and somitogenesis
5. organogenesis

Question 4

Congenital disease is caused by?

Answer 4

Defects during embryogenesis

Question 5

1. What happens in fertilisation phase?

Answer 5

Meiosis has been completed, with the formation of the second polar body and female pro nucleus
- before the development of the embryo proper the concepts must first implant then generate germ disc which takes about 10 days

Question 6

2. What happens during cleavage stage?

Answer 6

2 haploid pro nuclei fuse together (fertilised)
This is followed by first division = 2 cell zygote
Many division occurs once the 2 cell zygote divide to 12-16 cells (morula)
Compaction = embryo will sort themselves some stay in exterior and some within

Question 7

3. What happens in gastrulation?

Answer 7

Bilaminar germ disc (2 layers) made up of epiblast and hypoblast (primitive endoderm)becomes 3 layers as hypoblast becomes definitive endoderm and mesoderm.

• ectoderm = neutralisation
• mesoderm = muscles, bones, tissue
• endoderm = pharynx, oesophagus, colon,liver

Question 8

4. What happens in neuralisation?

Answer 8

Process in which gut formation and body folding happens (silk purse model)

Question 9

What is notochordal process?

Answer 9

Source of neural inducers
notochordal process excretes exctracellular substances which signals ectoderm to form neural plates
Neural folds rise out of plate of disk and fold to meet and fuse forming a neural tube

Question 10

What is the “cloth purse model”

Answer 10

septum and heart move from margin to centre
Yolk sac and stalk make umbilical cord
Prochordal and cloacal plates make boundaries of gut tube.

Question 11

5. What is organogenesis?

Answer 11

1. Differentiation of somatic derivatives - bones, muscles, tendons,
2. Development of sensory organs - ears, eyes, olfactory pits
3. Limb formation
4. Formation of facial structures
5. Genital structures formation