Embryology

Question 1

What is/describe gastrulation.

Answer 1

The process that converts a bilaminar disc to a trilaminar disc, the three layers being ectoderm, mesoderm, endoderm.

Question 2

How many layers are present after gastrulation?

Name them from top to bottom

Answer 2

Three
Ectoderm
Mesoderm
Endoderm

Question 3

How many layers are present prior to gastrulation?

Name them in order of top to bottom

Answer 3

Two
Epiblast
Hypoblast

Question 4

What process leads to the formation of three layers from two?
Describe what happens.

Answer 4

Invagination
Epiblast cells migrate to the primitive streak
They differentiate and divide and push through the epiblast layer
Come to form mesoderm (invagination)

Question 5

Where does implantation occur in placenta previa?

Answer 5

Posterior uterine wall

Question 6

What has the notochord developed from? (Which layer)

Answer 6

Mesoderm

Question 7

In what direction does development happen?

Answer 7

Cephalocaudally

Question 8

What ensures particular organs develop on a certain side?

Answer 8

The primitive node has ciliated cells which waft signalling molecules in a certain direction causing a cascade which leads to development on a certain side

Question 9

What is it called when organs develop on the opposite side?

Answer 9

Complete mirror imaging viscera

Question 10

What is complete mirror imaging viscera? When may it cause problems?

Answer 10

When the organs (viscera) have developed and so are present on the opposite side
Problem when mirror-imaging is incomplete (IE a mix of normal and mirror image)

Question 11

What features aid the movement of a zygote?

Answer 11

Fimbriae- sweep it along
Cilia- waft along
Muscular contractions of Fallopian tubes

Question 12

What surrounds the oocyte? What is its role?

Answer 12

Zona pellucida
Glycoprotein shell
 Prevents polyspermy
 Restricts size of cells from first few mitotic divisions
 Aids binding of sperm

Question 13

Which cells in an early embryo are totipotent?

Answer 13

Morulla (16 cell stage)

Question 14

Cells that are totipotent can…..

Answer 14

Develop or differentiate into anything

Question 15

At what pre-embryonic stage is a fertilised oocyte from IVF transferred into the uterus?

Answer 15

Morulla stage

Question 16

Which cells are pluripotent?

Answer 16

Blastocyst cells

Question 17

Before compaction it is called a morula, what is it called afterwards?

Answer 17

Blastocyst

Question 18

What process leads to the formation of a 16-cell morula?

Answer 18

Cleavage (mitotic divisions of the cells)

Question 19

What marks the onset of gastrulation?

Answer 19

The formation of the primitive streak

Question 20

What happens during compaction?

Answer 20

Fluid penetrates zona pellucida
Forms blastocoele cavity
Cells form tight junctions and form two masses- inner (embryoblast), outer (trophoblast)
This is now a blastocyst

Question 21

On which day does hatching occur? What is it and what does it facilitate?

Answer 21

Day 5
The blastocyst ‘hatches’ out of the zona pellucida
It is now free to enlarge and interact with endometrium

Question 22

After further differentiation, what layers do the embryoblast and trophoblast form? What is the name of one structure?

Answer 22

Inner (embryoblast)–> epiblast + hypoblast= bilaminar disc

Outer (trophoblas)–> syncitiotrophoblast + cytotrophoblast

Question 23

During the formation of the bilaminar disc, what cavity forms?

Answer 23

Primitive yolk sac

Question 24

What suspends the yolk sac? What will it later become?

Answer 24

Connecting stalk

Later becomes umbilical cord

Question 25

What is the difference between histiotrophic and haemotrophic?

Answer 25

Histiotrophictrophic nutrition is provided by the uterus

Haem is provided by exchange with the mother

Question 26

Around what day does implantation occur?

Answer 26

Day 10

Question 27

What occurs when some women get implantation bleeding?

Answer 27

Syncitiotrophoblast invades maternal sinusoids

The lacunae of the SYNC…fill with maternal blood and uteroplacental circulation has begun

Question 28

What is the name given to the exchange of nutrients through the placenta?

Answer 28

Uteroplacental circulation

Question 29

Where does the conceptus implant in placenta previa?

Answer 29

Lower uterine segment

Placenta develops over cervical opening

Question 30

Why is placenta previa a problem?

Answer 30

Can cause severe bleeding if baby presses on placenta

Needs C-section

Question 31

Why are ectopic pregnancies a great danger for the mum?

Answer 31

The conceptus, when trying to implant, will invade the surrounding tissue which is highly vascularised
TF great bleeding- haemorrhage

Question 32

Places for ectopic pregnancy And what is it?

Answer 32

Where blastocyst implants at a site outside of the uterus
Most commonly- Fallopian tube
Ovary, abdominal cavity

Question 33

At which stage does a fertilised oocyte implant?

Answer 33

Blastocyst

Question 34

What name change occurs when an egg is fertilised?

Answer 34

Oocyte–> zygote

Question 35

Define neurulation

Answer 35

Process by which the ectoderm thickens forming a neural plate which develops further into a neural tube
It is triggered by notochord signals

Question 36

What are the two general derivatives of ectoderm

Answer 36

Neuroectoderm

Surface ectoderm

Question 37

List some derivatives of the ectoderm layer

Answer 37

CNS/PNS
Epidermis
Lens of eye
Sweat glands
Hair/nails

Question 38

Which cavity forms during compaction?

Answer 38

Blastocoele cavity