Embryology 2.4

Question 1

Why was thalidomide harmful?

Answer 1

drug crosses placenta and interferes with angiogeneis

the limb buds that are being formed at the time suffer leading to short-flipper like limbs with missing digits or supernumerary digits

Question 2

What enantiomer causes birth defect?

Answer 2

(s) enantiomer , not (R) (does not cause birth defects)

Question 3

What is teratology?

Answer 3

study of when things go wrong during development

Question 4

What are teratogens?

Answer 4

environmental factors that cause abnormal development

Question 5

What are the percentage of reasons why abnormal development happens?

Answer 5

60%- unknown aetiology
10%- environmental
10%-genetic
20%-multifactorial

Question 6

Give examples of environmental factors?

Answer 6

drugs
alcohol
tobacco

infectious agents:
toxoplasma
rubella
cytomegalovirus
herpes

radiation

Question 7

Give example of genetic factors?

Answer 7

too many/ too few chromosomes
(turners syndrome- 45 chromosomes single X and downs syndrome 47 chromosomes trisomy 21)

structural changes-deletion of genes, segments of chromosomes

Causes
-increased maternal age
-damage from environmental factors (radiation e.g. x-ray)

Question 8

What are the three factors that determine the risk posed by a teratogen?

Answer 8

• exposure during critical periods of development
  -dosage of drug/chemical/factor
  -genetic constitution of embryo ie some more susceptible than others at equivalent doses

Question 9

What is the sensitivity of the different weeks of development?

Answer 9

weeks 1-2
-high risk of death, low risk from teratogens
weeks 3-8
-period of greatest sensitivity to teratogens
weeks 9-38
-decreasing sensitivity to teratogens

Question 10

Diagnosis ways of prenatal malformations?

Answer 10

blood- AFP (protein crosses into maternal)

ultrasound scan- 12 week anomaly scan

invasive tests: chorionic villus sampling and amniocentesis

Question 11

Diagnosis ways of postnatal malformations? (for babies)

Answer 11

hip stability
testes (descent)
fingers and toes
hearing

Question 12

What happens in each week?

Answer 12

week 1 - blastocyst forms and moves to uterine cavity

week 2 - bilaminar embryo, implantation, placenta formation

week 3- gastrulation, neurulation, somite formation

week 4 - folding of embryo, organogenesis