Weeks 2-8

Question 1

What does the dorsal side of the body refer to?

Answer 1

The back.

Question 2

What plane divides the body into right and left halves?

Answer 2

Median plane.

Question 3

What is the function of the coronal plane?

Answer 3

It divides the body into anterior (ventral) and posterior (dorsal) parts.

Question 4

When does the blastocyst embed into the uterine lining?

Answer 4

Begins at day 7.

Question 5

Name the two layers of the trophoblast.

Answer 5

Cytotrophoblast (inner layer) and syncytiotrophoblast (outer layer).

Question 6

What hormone does the syncytiotrophoblast produce?

Answer 6

Human chorionic gonadotrophin (hCG).

Question 7

By which day is the blastocyst fully embedded in the endometrium?

Answer 7

By day 10.

Question 8

What are primary chorionic villi?

Answer 8

Structures that develop on days 13–14 and are part of the placental tissues.

Question 9

What marks the beginning of secondary chorionic villus development?

Answer 9

Mesodermal cells penetrate the core of primary villi at the start of week 3.

Question 10

What are the two layers of the inner cell mass?

Answer 10

Hypoblast (adjacent to the blastocyst cavity) and epiblast (adjacent to the amniotic cavity).

Question 11

What structure forms the floor of the amniotic cavity?

Answer 11

The epiblast.

Question 12

What happens to the primary yolk sac during embryogenesis?

Answer 12

It decreases in size as the secondary yolk sac forms.

Question 13

What is the role of the extraembryonic somatic mesoderm?

Answer 13

It lines the trophoblast and covers the amnion, forming the chorion.

Question 14

When does gastrulation occur?

Answer 14

During the third week of development.

Question 15

What germ layers are formed during gastrulation?
MEE

Answer 15

Mesoderm
Ectoderm
Endoderm

Question 16

What does the ectoderm give rise to? REN

Answer 16

Retina
Epidermis
Nervous system

Question 17

What does the mesoderm give rise to? CBSS

Answer 17

Connective tissues
Blood vessels
Smooth muscle
Skeletal structures.

Question 18

What does the endoderm give rise to?

Answer 18

Epithelial linings of the respiratory and gastrointestinal tracts.

Question 19

What is the primitive streak?

Answer 19

A narrow groove that appears on days 15–16, signaling the site of mesoderm formation.

Question 20

What can a remnant of the primitive streak lead to?

Answer 20

Sacrococcygeal teratoma.

Question 21

What is the notochord?

Answer 21

A structure that serves as the basis for the axial skeleton and induces the formation of the neural plate.

Question 22

What happens to the notochordal canal during its development?

Answer 22

It fuses with the endoderm, allowing communication with the yolk sac.

Question 23

What does the allantois become as the bladder enlarges?

Answer 23

The urachus.

Question 24

What are the blood vessels of the allantois associated with?

Answer 24

Umbilical arteries and vein.

Question 25

What is ectopic pregnancy?

Answer 25

Implantation of the blastocyst outside the uterine cavity, commonly in the fallopian tube.

Question 26

What is the incidence of ectopic pregnancies?

Answer 26

Varies from 1:80 to 1:250 pregnancies.

Question 27

What is the main cause of embryo loss during the first three weeks?

Answer 27

Abnormal conceptuses or chromosomal abnormalities.

Question 28

What is embryonic folding?

Answer 28

A process where the flat embryonic disc transforms into a cylindrical embryo.

Question 29

What is the significance of the prechordal plate?

Answer 29

It marks where the ectoderm and endoderm meet and contributes to head development.

Question 30

What are Carnegie stages?

Answer 30

Stages of embryonic development based on clinical features rather than size or age.

Question 31

At what stage does the notochordal process develop?

Answer 31

Stage 8, around days 19–21.

Question 32

What is the function of the neural plate?

Answer 32

It gives rise to the brain and spinal cord.

Question 33

What triggers the development of the neural plate?

Answer 33

Induction by the notochord.

Question 34

What is the main role of the syncytiotrophoblast?

Answer 34

To erode maternal tissues for implantation and produce hCG.

Question 35

When does the secondary yolk sac form?

Answer 35

After the primary yolk sac reduces in size.

Question 36

What defines the boundaries of the embryonic disk?

Answer 36

The epiblast and hypoblast layers.

Question 37

What are intravillous spaces?

Answer 37

Cavities in the chorion filled with maternal blood for nutrient exchange.

Question 38

When does the embryo first establish a connection to the placenta?

Answer 38

By the end of the third week, with the formation of blood vessels in chorionic villi.

Question 39

What are the main contributors to maternal-placental abnormalities?

Answer 39

Adhesions, scarring, or infections delaying zygote transport.

Question 40

What determines the differentiation of the embryonic germ layers?

Answer 40

Continuous migration of cells from the primitive streak.