Embryology

Question 1

What two periods is embryogenesis split into?

Answer 1

1. Embryonic period (first 8 weeks)

2. Foetal period (final 32 weeks)

Question 2

How does fertilisation occur?

Answer 2

1. Sperm cell meets corona radiata of egg
2. Acrosome release enzymes that break down the zona pellucida
3. Sperm and egg membranes fuse

Question 3

Name the different stages of development of the embryo

Answer 3

• Fertilised ovum (up to 24 hrs)
• Cleavage (up to day 3)
• Morula (up to day 4)
• Blastocyst (up to day 5)

Question 4

What is the blastocystic stage?

Answer 4

On days 7-8, the syncytiotrophoblast secretes enzymes that allow implantation

Question 5

What is gastrulation?

Answer 5

Formation of 3 germ layers at end of week 2

Question 6

What is the neural tube?

Answer 6

The beginning of the CNS

Question 7

Name 2 neural tube defects

Answer 7

• Spina bifida

- Anencephaly

Question 8

What is the usual dose of folic acid?

Answer 8

400mcg

5mg if risk factors present

Question 9

Give some risk factors for NTDs

Answer 9

• Family/personal history
• Diabetes
• BMI >35
• Anti-epilepsy medication
• Coeliac disease

Question 10

What are some other ways of intaking folate?

Answer 10

• Vegetables
• Fruits
• Legumes
• Cereal
• Nuts
• Yeast extracts

Question 11

What is a teratogen? Give 2 examples

Answer 11

Something that causes congenital malformations during embryonic development

• Accutane
• Thalidomide

Question 12

What does the neural tube close?

Answer 12

Between weeks 3 and 4

Question 13

What hormone indicates pregnancy and where is it produced?

Answer 13

• hCG

- Syncytiotrophoblast

Question 14

When does the heart generally start beating?

Answer 14

Week 4-5

Question 15

What does the blastocyst split into?

Answer 15

• Trophoblast (forms placenta and chorion)

- Inner Cell Mass/Embryoblast (forms foetus, umbilical cord and amnion)

Question 16

What processes happen to produce a female foetus?

Answer 16

• Oestrogen causes formation of external genitalia
• Walffian ducts passively regress
• Mullerian ducts passively develop into internal genitalia

Question 17

What processes happen to produce a male foetus?

Answer 17

• SRY gene activated which forms the testis
• MIH is released which causes the active regression of Mullerian ducts
• Testosterone causes active development of Walffian ducts into internal genitalia and releases 5 aDHT which causes active development of external genitalia