Embryology - 2

Question 1

What is embryogenesis?

Answer 1

First eight weeks of embryo development post fertilisation

Question 2

Describe week 2-3 in embryoblast development

Answer 2

Formation of bilaminar disc and development of amniotic sac, yolk sac, extraembryonic mesoderm and chorionic cavity

Question 3

Describe week 3-4 in embryoblast development

Answer 3

Differentiation of bilaminar disc into trilaminar structure - 3 germ layers through process of gastrulation and neural tube formation

Question 4

What happens in week 5-8 of embryoblast development?

Answer 4

Organogenesis

Question 5

What period begins after week 8 of embryoblast development?

Answer 5

Foetal period

Question 6

What cells are in the inner cell mast of the blastocyst?

Answer 6

Pluripotent cells

Question 7

What is the fluid filled cavity of blastocyst?

Answer 7

Blastocoele

Question 8

What does the inner cell mass differentiate into?

Answer 8

Bilaminar epiblast and hypoblast
2 cavities form - yolk sac on side of hypoblast and amniotic cavity on side of epiblast

Question 9

What does the epiblast differentiate into?

Answer 9

3 germ layers - ectoderm, mesoderm and endoderm in process of gastrulation - day 13 to 16

Question 10

What does gastrulation start with?

Answer 10

Groove appearing in the caudal end of the epiblast called the primitive streak

Question 11

How is the endoderm formed?

Answer 11

Epiblast cells migrate into hypoblast layer displacing them

Question 12

How is the mesoderm formed?

Answer 12

Epiblast cells migrate through primitive streak between the epiblast and hypoblast

Question 13

What is the gastrula?

Answer 13

Newly formed trilaminar disc with 3 layers which forms the different organ systems

Question 14

What does the ectoderm give rise to?

Answer 14

Epidermis, CNS, PNS, hair, nails, neuroendocrine organs and enamel of teeth

Question 15

What does mesoderm give rise to?

Answer 15

Dermis, musculoskeletal structures, CVS, kidneys, ureters, bladder, gonads, adrenal cortex, visceral and parietal linings

Question 16

What does endoderm give rise to?

Answer 16

Lining of gastrointestinal tract, parenchyma of liver, pancreas, thyroid, parathyroid, tonsils, thymus, bladder and urethra

Question 17

What are the major subunits of the mesoderm?

Answer 17

Paraxial mesoderm
Intermediate mesoderm - kidneys, gonads and ureter
Lateral plate mesoderm

Question 18

What are the 2 reasons for multiple pregnancy to occur?

Answer 18

Dizygotic - two or more eggs fertilised and implanted so non-identical
Monozygotic - one embryo splits into 2 so identical

Question 19

What does the monozygotic twin types depend on?

Answer 19

The timing of the single embryo dividing

Question 20

What is the type of twin is it if division day is day 1-4?

Answer 20

Dichorionic diamniotic - 20% incidence
Separate placenta and amniotic

Question 21

What type of twin is it if division day is day 5-8?

Answer 21

Monochorionic diamniotic - 75%
Share placenta and separate amniotic sac

Question 22

What type of twin is it if division day is day 7-14?

Answer 22

Monochorionic monoamniotic - 5%
Share placenta and amniotic sac

Question 23

What type of twin is it if division day is more than 14 days?

Answer 23

Conjoined twins - less than 1%