8 - Embryology I

Question 1

At how many weeks is the:

• Pre-embryonic period?
• Embryonic period?
• Fetal period?

Answer 1

• Pre-embryonic period - first 2 weeks
• Embryonic period - weeks 3-8
• Fetal period - weeks 9-38

Question 2

Where is the oocyte released and what tube does it travel along?

Answer 2

Released from ovary into fallopian tube

Question 3

Where does fertilisation occur?

Answer 3

In the ampulla of the fallopian tube

Question 4

What is a fertilised oocyte known as?

Answer 4

Zygote

Question 5

Where is the normal site of zygote implantation?

Answer 5

Posterior uterine wall

Question 6

How long after fertilisation does the first cell division take place?

Answer 6

~30 hours after fertilisation

Question 7

What is the zona pellucida and what does it do?

Answer 7

Glycoprotein shell around the oocyte

Excludes all other sperms cells upon fertilisation

Question 8

What is a morula?

Answer 8

• Solid ball of cells resulting from divisions after fertilisation
• All cells are totipotent (can become anything)

Question 9

What is the next structure to form after a morula? What is this?

Answer 9

Morula forms a blastocyst

• Forms the first cavity
• Hollow structure of cells with an inner cell mass (embryoblast) and outer cell mass (trophoblast)
• Cells are now pluripotent (can become many cell types but not any)

Question 10

After 1 week, the blastocyst hatches from the ……. …………… so implantation can occur into the uterine epithelium

Answer 10

Zona pellucida

Question 11

What does the trophoblast (outer) layer of the blastocyst do?

Answer 11

Provides nutrients to the embryo and develops into the placenta

Question 12

What occurs during implantation?

Answer 12

The blastocyst adheres to the wall of the uterus and invades the endometrium

Question 13

The trophoblast (outer) layer of the blastocyst separates into two layers. What are they and what do they do?

Answer 13

Cytotrophoblast - inner trophoblast, penetrates the maternal spiral arteries to route blood to the placenta

Syncytiotrophoblast - outer trophoblast, invades the wall of the uterus to establish nutrient flow

Question 14

The embryoblast (inner cell mass) forms a bilaminar disc. What are the two layers?

Answer 14

• Epiblast

- Hypoblast

Question 15

What two cavities are formed by formation of the bilaminar disc? Which side is each one on?

Answer 15

Amniotic sac - above epiblast

Yolk sac - below hypoblast

Question 16

Which of the two layers goes on to form the trilaminar disc? What are the three layers?

Answer 16

The epiblast

• Ectoderm
• Mesoderm
• Endoderm

Question 17

What are the layers of the trilaminar disc also known as?

Answer 17

Germ layers

Question 18

What is the process of formation of the trilaminar disc from the bilaminar disc called?

Answer 18

Gastrulation

Question 19

What structure forms on the surface of the epiblast during gastrulation? What is its purpose?

Answer 19

The primitive streak (beginning at the primitive node)

• Promotes invagination of the epiblast to form the trilaminar disc

Question 20

What structures of the body are derived from ectoderm?

Answer 20

• Nervous system

- Epidermis

Question 21

What structures of the body are derived from mesoderm?

Answer 21

• Muscle
• Cartilage
• Bone
• Vasculature

Question 22

What structures of the body are derived from endoderm?

Answer 22

• Epithelial lining of internal tracts (e.g. GI and respiratory tracts)