Mechanisms of Disease during Embryogenesis

Question 1

What are the 2 main periods of human development?

Answer 1

Two main periods:
Embryonic period:
• Up to the end of week 8
• Most of the organogenesis occurs in these first 8 weeks

Fetal period:
• The remaining time in utero
• Involves growth and modeling

Defects during embryogenesis result in congenital malformations

Question 2

Mechanisms of development

Answer 2

From egg: 
fertilisation
cleavage 
gastrulation 
neurulation and somitogenesis 
organogenesis - to an adult

Question 3

The fertilised zygote

Answer 3

diagrams

Question 4

Cleavage stage

Answer 4

morula and blastocyst

diagrams

Question 5

Gastrulation

Answer 5

Gastrulation: from 2 layers to 3. Hypoblast
(primitive endoderm) is displaced by involuting cells that become definitive endoderm, and mesoderm
diagram

Question 6

Neurulation

Answer 6

diagrams

Neurulation is concomitant with other form-shaping (morphogenetic) processes, particularly gut formation and body folding (“silk purse” model)

Question 7

Organogenesis

Answer 7

• Differentiation of somitic derivatives 
– bones, muscles, tendons
• Development of sensory organs 
– ears, eyes, olfactory pits
• Limb formation
– forelimbs first, hindlimbs next
– establishment of pattern in the limbs: proximodistal, anterior-posterior, dorsal-ventral
• Formation of face structures 
– jaws, nose, tongue, palate
• Formation of genital structures

Question 8

Desirable characteristics of a model organism

Answer 8

• Relevance/representative
• Accessibility/availability
• Experimental manipulation
• Genetics
• Cost/space

Question 9

The most widely used models

Answer 9

1) bilateria
2a) Deuterostomes - chordates

diagram