Embryology

Question 1

what is the pre-embryonic period?

Answer 1

From fertilisation to the trilaminar disc stage

1-3 weeks

Question 2

what is the embryonic period?

Answer 2

From the trilaminar disc stage to the foetal stage
4-8 weeks
rapid growth and differentiation
organogenesis
period where defects can occur and the foetus is susceptible to pharmacological change

Question 3

what is the foetal period?

Answer 3

The consolidation and growth of the baby

9 weeks - term

Question 4

what is the difference between fertilisation age and menstrual age?

Answer 4

Menstrual age: time since the first day of mothers last period
Fertilisation age: time at which the ovum was actually fertilised
Menstrual age is two weeks more than the fertilisation age

Question 5

Describe the structure of the egg

Answer 5

Cumulus: outside layer of cells which the nourish and support the egg as it develops
Zona pellucida: special membrane
Oocyte plasma membrane: surrounds the egg and has specific receptors for sperm

Question 6

How does fertilisation occur?

Answer 6

1. acrosome full of enzymes bursts in head of sperm upon contact with egg
2. sperm penetrates zona pellucida
3. binds to receptors on oocyte membrane so egg and sperm fuse
4. zona pellucid thickens to prevent polyspermy
5. receptors withdraw
6. fusion of nuclei- 46 chromosomes

Question 7

how many cells make a morula?

Answer 7

16

Question 8

cell types within a blastocyst?

Answer 8

embryoblasts (inner cell mass)

trophoblasts

Question 9

what happens if the zona pellucida is damaged at the blastocyst stage?

Answer 9

The cells separate but share the same placenta so you get monozygotic twins

Question 10

when does the blastocyst implant into the endometrium?

Answer 10

day 6

Question 11

How does the blastocyst receive nutrients from the mother?

Answer 11

diffusion

Question 12

what is an ectopic pregnancy?

Answer 12

implantation in an abnormal site

Question 13

The inner cell mass differentiates into..?

Answer 13

Epiblasts and hypoblasts

Question 14

the trophoblasts become..?

Answer 14

syncitiotrophoblasts which grow into the endometrium and cytotrophoblasts

Question 15

where is the amniotic cavity found?

Answer 15

in the middle of the epiblasts cells

Question 16

what is the coagulation plug?

Answer 16

once the embryoblast has fully implanted into the endometrium, the coagulation plug holds it to the wall to prevent it from moving back out into the uterus.

Question 17

what membrane is formed when the hypoblast cells grow back towards the coagulation plug?
what is formed when there is a second wave of hypoblasts cell growth?

Answer 17

Haussers membrane- within is the primary yolk sac

secondary yolk sac and the primary yolk sac dissipates

Question 18

when does gastrulation occur?

Answer 18

end of week 2

day 13-14

Question 19

what is the role of the trophoblasts?

Answer 19

The trophoblast layer produces HCG

It stimulates the corpus luteum to produce oestrogen and progesterone to maintain the endometrium

Question 20

why do the mothers WBC not attack the ‘foreign’ embryo?

Answer 20

the syncitiotrophoblasts form a barrier which prevent the WBC from passing. keeping the maternal and foetal blood flow separate. They switch off genes which would trigger an immune response also.

Question 21

how does the mesoderm develop?

Answer 21

primitive streak appears on the ectoderm (epiblast cells). These cells migrate down and out between the ectoderm and endoderm. forming another layer called the mesoderm. This creates a trilaminar disc.

Question 22

Describe the steps of neurolation

Answer 22

Underneath the primitive streak, mesoderm cells differentiate to form the notochord.
Induces the thickening of the above ectoderm to form the neural plate.
The neural plate sinks into the mesoderm to form the neural tube (week 3)

Question 23

What do the neural crest cells go on to become?

Answer 23

melanocytes, dorsal root ganglion, adrenal medulla

Question 24

Name three neural tube defects

Answer 24

1. Hydrocephalus: water in the brain
   Cerebral hemispheres swell up
   Impaired development of cerebral cortex
2. Microcephaly: small brain
3. Anencephaly: most of the brain is absent
   failure of front end of neural tube to close

Question 25

when does the embryo fold craniocaudally and laterally?

Answer 25

end of week 3

Question 26

what do the three germ layers become

Answer 26

Endoderm: respiratory tract and GI tract
Paraxial mesoderm: muscle, skin, skeleton apart from cranium (vertebrae), connective tissue
Intermediate mesoderm: urogenital system
Lateral mesoderm: abdominal wall
Ectoderm: skin, nervous system

Question 27

3 degrees of spina bifida

Answer 27

Occulta
Meningocoel
Myelocoel

Question 28

At what point can sexing of the baby happen?

Answer 28

fifth month

Question 29

At what point can a heartbeat be heard?

Answer 29

day 22