Mechanisms of disease during embryogenesis

Question 1

What are the 2 periods of human development?

Answer 1

1. Embryonic period - up to end of week 8 and where organogenesis occurs
2. Foetal period - remaining time in utero involving growth and modelling

Question 2

What can defects during embryogenesis result in?

Answer 2

Congential malformation

Question 3

Describe the first stage of development: fertilized zygote

Answer 3

Question 4

What happens during the cleavage stages?

Answer 4

Question 5

How does the blastocyst give rise?

Answer 5

Embryo makes its way to the uterus taking 10 days giving rise to blastocyst

Question 6

What happens during gastrulation?

Answer 6

Gastrulation leads to 3 layers of cells

• At one end of bilaminar germ disk the primitive groove forms, the cells will go below the epiblast and hypoblast layer and form the endoderm and mesoderm

Question 7

What happens during neurulation?

Answer 7

In the ectoderm the neural plate is established

• Neural plate folds meet and fuse to create neural tube underneath the ectoderm
• Mesoderm cells start to condense in tissue blocks - precursors of bones

Question 8

What happens with body folding during the neurulation stage?

Answer 8

Mesoderm and endoderm will give rise to all internal organs - so the whole embryo needs to fold over = body folding - so mesoderm and endoderm are protected and covered

Folding leads to the formation of umbilical cord and the mid-gut

Question 9

What happens during organogensis?

Answer 9

• Differentiation of somitic derivatives - bones, muscles, tendons
• Development of sensory organs - ears, eyes and olfactory pits
• Limb formation - forelimbs then hindlimbs
• Formation of face structures - jaw, nose tongue and palate
• Formation of genital structures

Question 10

What are the different stages of development?

Answer 10

From egg…

1. Fertilisation
2. Cleavage
3. Gastrulation
4. Neurulation
5. Organogenesis

…To adult

Question 11

What are the desirable characterisitics of a model organism?

Answer 11

• Representative
• Accessibility/availability
• Experimental manipulation
• Good understanding of genetics
• Cost/space

Question 12

Why are zebrafish used to model human disease?

Answer 12

• Easy to maintain in lab conditions
• Over 70% of human genes have an homolog in the fish
• Transparent embryo can see a lot

Question 13

What are the different genetic or environmental factors for congential disease?

Answer 13

• Single gene mutations - one gene will be enough to display a characteristic defect
• Chromosomal anomalies - whole chromosomal rearrangements are responsible for a disease (eg. chromosome 21 leading to down syndrome)
• Polygenic disorders - several different genes simultaneously affected which causes the disease

Environmental - deleterious influence of the environment on a particular process eg. diet, infection, toxic compounds

Often, it is a combination of genetic and environmental causes what results in congenital disease.