Embryology

Question 1

Name for fertilised egg up to week 8?

Answer 1

Embryo

Question 2

Name for fertilised egg from week 9 onwards?

Answer 2

Foetus

Question 3

Name the 6 stages of embryogenesis?

Answer 3

Gametogenesis, fertilisation, cleavage, gastrulation, morphogenesis and organogenesis

Question 4

When does cleavage start and what 2 things happens?

Answer 4

• Within 1-4 days
• Cells divide to form a morula then blastocyst
• Compaction occurs when cell junctions form and fluid supplies outer cells

Question 5

Number of cells in a morula + blastocyst?

Answer 5

> 16 + > 100

Question 6

Number of cell said to be totipotent in an embryo?

Answer 6

Up to 8

Question 7

When does gastrulation occur and what happens?

Answer 7

Week 3 and germ layers form

Question 8

Name the 3 germ layers?

Answer 8

Endoderm, mesoderm and ectoderm

Question 9

What happens in morphogenesis + when does it occur?

Answer 9

Embryo folds from flat shape into a tube + week 4

Question 10

What happens in organogensis?

Answer 10

Organs form

Question 11

3 steps of sperm entering an egg?

Answer 11

• Sperm binds to zona pellucida
• Sperm releases acrosomal enzymes which allow sperm into egg and fusion
• Egg releases cortical granules to prevent more sperm binding

Question 12

Where does a blastocyst normally implant and what happens straight after implantation?

Answer 12

Upper dorsal uterus and hatching (sheds zona pellucida)

Question 13

Name the outer layer of a blastocyst and its 2 sublayers?

Answer 13

Trophoblast and cytotrophoblast + synctiotrophoblast

Question 14

Which blastocyst layer is the outermost and attaches to the uterine wall?

Answer 14

Synctiotrophoblast

Question 15

Name the inner layers + associated surfaces of a blastocyst?

Answer 15

Epiblast (dorsal) and hypoblast (ventral)

Question 16

What forms the amniotic cavity?

Answer 16

The epiblast

Question 17

What forms the yolk sac + definitive yolk sac?

Answer 17

The hypoblast

Question 18

What is the main cavity that surrounds the yolk sac + amniotic cavity and what does it grow inside?

Answer 18

The chorionic cavity + extraembryonic mesoderm

Question 19

By what day is implantation complete?

Answer 19

9

Question 20

By what day does the definitive yolk sac start to form?

Answer 20

13

Question 21

Layer that the chorionic cavity forms under the cytotrophoblast?

Answer 21

Extraembryonic mesoderm

Question 22

2 structures that form on the epiblast by week 2 + function?

Answer 22

Oropharyngeal membrane (forms mouth) + primitive streak (needed for gastrulation/germ layer formation)

Question 23

How do the germ layers arise?

Answer 23

• Cells move down via primitive streak
• Replace hypoblast with endoderm
• Replace epiblast with ectoderm
• Mesoderm is the middle layer

Question 24

Ectoderm becomes the?

Answer 24

Skin + nervous system

Question 25

Mesoderm becomes the?

Answer 25

Tissues e.g. bone, muscle

Question 26

Endodoerm becomes the?

Answer 26

Lining of the GI, resp and urinary tract

Question 27

Lateral folding forms what 2 things?

Answer 27

Thoracic and abdominal cavity

Question 28

Cranial folding does what 2 things?

Answer 28

Forms the foregut + moves heart tube into thoracic cavity

Question 29

Caudal folding forms what 3 things?

Answer 29

Hindgut, anus and umbilical cord

Question 30

What is epigenetic control?

Answer 30

Preferential expression of either the maternal or paternal copy of a gene

Question 31

Type of junction that form during compaction + function?

Answer 31

Gap junctions + allows fluid to reach outer cells in the morula/blastocyst

Question 32

Order of 3 folding movements?

Answer 32

Lateral, cranial and caudal

Question 33

What week during development has the highest risk of inducing a birth defect?

Answer 33

Week 5

Question 34

What organ is the most common to be affected by birth defects?

Answer 34

The heart

Question 35

What makes up the Tetralogy of Fallot + associated condition?

Answer 35

Pulmonary stenosis, right ventricular hypertrophy, overriding aorta and VSD + DiGeorge syndrome