Embryology

Question 1

When does the embryonic period occur?

Answer 1

Weeks 3-8

Question 2

When does the Foetal period occur?

Answer 2

Weeks 9- end

Question 3

Briefly describe what happens in fertilisation

Answer 3

An oocyte (released from the ovary) is invaded by a sperm cell in the fallopian tube.

Question 4

Where is the ideal implantation site for the zygote?

Answer 4

The posterior uterine wall

Question 5

When does cleavage of a zygote begin?

Answer 5

30 hours after fertilisation

Question 6

What is a zona pellucida and what is its function?

Answer 6

A glycoprotein shell that protects the zygote from the reproductive tract and fertilisation by more sperm cells.

Question 7

What is a morula?

Answer 7

A clump of totipotent cells (developed from the initial zygote)

Question 8

What occurs on day 4 after fertilisation?

Answer 8

Compaction- first cavity formed- morula becomes a blastocyst

Question 9

In a blastocyst, to what extent can the cells differentiate?

Answer 9

The cells are pluripotent (can become many but not all cell types)

Question 10

When is the zona pellucida no longer needed?

Answer 10

Day 5

Question 11

On what day do the cells implant in the uterine wall?

Answer 11

Day 6-7

Question 12

Of a conceptus made up of 107 cells, how many will become the embryo?

Answer 12

8 cells

Question 13

In week 2 of development, what does the outer cell mass differentiate into?

Answer 13

Syncytiotrophoblast

Cytotrophoblast

Question 14

In week 2 of development, what does the inner cell mass differentiate into?

Answer 14

The bilaminar disk- hypoblast and epiblast

Question 15

When is the amniotic cavity formed?

Answer 15

Day 8

Question 16

What is the importance of the placenta?

Answer 16

Maternal flow is established for oxygen and other nutrients

Question 17

Briefly describe what is meant by an ectopic pregancy

Answer 17

Implantation occurs away from the uterine body (eg. Fallopian tubes)
The tubes can rupture causing haemorrhage

Question 18

Briefly describe what happens in placenta praevia

Answer 18

The conceptus implants in the lower uterine section
The placenta blocks the normal cervical opening
Risk of haemorrhage
Needs a C-section delivery

Question 19

On what day of development do blood vessels infiltrate the syncytiotrophoblast?

Answer 19

Day 12

Question 20

What week has the highest risk for congenital abnormalities to occur?

Answer 20

Week 3

Question 21

What happens in gastrulation?

Answer 21

The bilaminar disc becomes the trilaminar disc

The axes are established

Question 22

What appears to start gastrulation?

Answer 22

The primitive streak

Question 23

Where does the primitive streak appear?

Answer 23

Dorsal surface of the epiblast

Question 24

What are the three layers of the trilaminar disc called?

Answer 24

Ectoderm
Mesoderm
Endoderm

Question 25

What is the notochord?

Answer 25

A solid rod of cells in the midline of the trilaminar disc. It is the basis for the axial skeleton and drives the formation of the nervous system

Question 26

What develops from the ectoderm?

Answer 26

Organs | Structures that maintain contact with the outside world eg. nervous system, epidermis

Question 27

What develops from the mesoderm?

Answer 27

Supporting tissues- muscles, cartilage, bone, vascular system

Question 28

What develops from the endoderm?

Answer 28

Internal structures eg. respiratory tract, lining of GI tract

Question 29

What happens in the condition known as situs inversus?

Answer 29

Complete mirror image of organs

Question 30

Describe the 2 ways twins can form

Answer 30

Embryo splits after first cleavage- 2 placentas OR Inner cell mass duplicates- 1 shared placenta

Question 31

What is teratogenesis?

Answer 31

The process through which normal embryonic development is disrupted

Question 32

How does the ectoderm start to form the nervous system?

Answer 32

A neural plate forms which then differentiates and folds into the neural tube

Question 33

What are somites?

Answer 33

The organisation of paraxial mesoderm into segments

Question 34

How many somites are present at final development?

Answer 34

31 pairs

Question 35

The somite differentiates further to form 3 more discrete areas. What are these called?

Answer 35

Dermatome Myotome Sclerotome

Question 36

What is the developmental definition of the word 'myotome'?

Answer 36

Myotome is tissue that gives rise to muscles

Question 37

What is the developmental definition of the word 'dermatome'?

Answer 37

The part of the somite that gives rise to the dermis

Question 38

What does paraxial mesoderm differentiate into?

Answer 38

Axial skeleton, dermis, muscles of body wall, some limb muscles

Question 39

What does intermediate mesoderm differentiate into?

Answer 39

Urogenital system eg. kidneys, ureters, gonads

Question 40

What does lateral plate somatic mesoderm differentiate into?

Answer 40

Connective tissue

Question 41

What does lateral plate splanchnic mesoderm differentiate into?

Answer 41

Smooth musculature, connective tissue, vasculature of gut

Question 42

What does embryological folding achieve?

Answer 42

Draws together the margins of the disc | Embryo becomes suspended within the amniotic sac

Question 43

How long does the pre-embryonic period last?

Answer 43

First 2 weeks