Integration of information- embryology

Question 1

What forms when the blastocyst implants?

Answer 1

Syncytiotrophoblast

Question 2

What does the embryo consist of?

Answer 2

A bilaminar disc (epiblast and hypoblast)

- it’s a circular disc

Question 3

In terms of embryonic development, what has developed by day 15/16?

Answer 3

Formulation of a trilaminar disc via gastrulation- it is now elongated in the anterior/posterior direction
Buccopharyngeal membrane begins to develop
Towards the tail of the embryo, there is a primitive streak which is a cleft between the cells in the epiblast layer

Question 4

What is the result of gastrulation?

Answer 4

3-layered embryo which gives rise to three germ types- mesoderm, ectoderm and endoderm

Question 5

What moves through the primitive streak?

Answer 5

Cells from the epiblast- they move through the primitive streak into a gap that’s opened up between the epiblast and hypoblast

Question 6

What happens when cells from epiblast move through primitive streak?

Answer 6

They undergo differentiation to form mesoderm cells
There are multiple layers of cells moving, implying there’s proliferation in the epiblast before they move into the streak.

Question 7

What does ectoderm give rise to?

Answer 7

Skin and CNS

Question 8

What does the mesoderm give rise to?

Answer 8

Skeleton, muscle, kidney, heart and blood

Question 9

What does the endoderm give rise to?

Answer 9

Gut, liver and lungs

Question 10

How has the embryonic disc grown by day 21?

Answer 10

The embryo has elongated a lot and there is differentiation of the mesodermal cells between the primitive node and the buccopharyngeal membrane to form the notochord

Question 11

What does the notochord go on to develop in simple organism and also most vertebrates?

Answer 11

In simplest organisms, the notochord is the CNS but in most other vertebrates, the notochord directs the formation of the CNS

Question 12

When does formation of CNS begin?

Answer 12

Around day 17

Question 13

What does the ectoderm undergo differentiation to form?

Answer 13

Neural cells

Question 14

What does the neural plate do after it has expanded?

Answer 14

It begins to fold at around day 21- there is a cleft in the middle of the neural plate which occurs above the notochord

Question 15

What effect does the notochord have on near cells?

Answer 15

It stops the change of cells- they stop proliferating/differentiating- To hold base of the to-be-neural tube in place

Question 16

What is cell activity like in the neural folds?

Answer 16

There’s movement and differentiation of cells which are becoming prominent over next few days

Question 17

When do neural folds stop expanding?

Answer 17

When they meet each other to form the tube above the notochord- this becomes the CNS

Question 18

Around day 19, what is the mesoderm doing?

Answer 18

The mesoderm is continuing to proliferate rapidly while neural folds are developing as it will form the major components of the body (trunk, muscles, bones etc)

Question 19

How does the amnion change?

Answer 19

The amnion initially lies mainly over the embryo but around day 19, the amnion seems to have a more rounded structure surrounding the embryo at the top
By day 21, most of the embryo is within the amniotic cavity

Question 20

How do the changes in the amnion occur?

Answer 20

The amnion moves down and around the embryo and the embryo also moves upwards

Question 21

What is the yolk sac connected to?

Answer 21

Digestive system as it provides nutrients

Question 22

How important is the yolk sac in humans?

Answer 22

Not vital as it’s not only source of nutrients

Question 23

What happens at day 28, in terms of amniotic cavity?

Answer 23

It completely surrounds the embryo

Question 24

What happens to the yolk sac at day 28?

Answer 24

It doesn’t get cut off but it is believed that the amnion fuses around the yolk sac

Question 25

What is found where the amnion fuses around the yolk sac?

Answer 25

It leaves a defect and this is the same place where the umbilical cord os found

Question 26

In terms of neurulation, what happens around day 22?

Answer 26

From the middle of the embryo, the neural tube begins to zip up- ~day 23, there is still an anterior and posterior neuropore but these close over next week.

Question 27

What develops at this stage near the anterior neuropore?

Answer 27

Brain development

Question 28

What can be seen in the neural tube when it has zipped up?

Answer 28

The pericardial bulge- the heart develops here

Question 29

What happens to the embryo around day 25-28?

Answer 29

It begins to curve in a head to tail direction

Question 30

What begins to develop around the base of the mesoderm at around day 25?

Answer 30

Kidney and reproductive system

Question 31

What begins to develop around the top of the mesoderm at around day 25?

Answer 31

The heart

Question 32

What stage of development is the embryo at by day 28?

Answer 32

The curve is clear cut There's a heart bulge, the lens of the eyes are beginning to develop, the otic placode where the ears will develop; the pharyngeal arches are developing where the vasculature begins, the limb ridges are also visible. Clearly visible tail

Question 33

Where does the angiogenic cell cluster which gives rise to vasculature begin?

Answer 33

Slightly outside the embryo

Question 34

What brings the angiogenic cell cluster into the body cavity of the embryo?

Answer 34

Folding of the head

Question 35

What does the folding of the tail bring into the body cavity?

Answer 35

The cloacal membrane which gives rise to kidneys and reproductive system- connecting stalk and yolk sac enter the body cavity at the same site

Question 36

Where are the primitive blood vessels which give rise to endocardial tubes located?

Answer 36

On the side of the embryo

Question 37

What controls development?

Answer 37

All the processes are controlled by signals from genes- complex gene interactions occur throughout development to form a foetus

Question 38

What are the Hox genes involved in?

Answer 38

``` Establishing: - A-P axis - Differences in vertebrae - CNS divisions - Pattern the limbs It is involved in patterning (how cells relate to one another) ```

Question 39

Why is a women's diet important in development?

Answer 39

One of the signals that controls the activation of Hox genes is retinoic acid, a derivative of vitamin A- so without vitamin A, Hox genes may not function properly

Question 40

When do the forelimb and hindlimb buds appear?

Answer 40

Forelimb ~day27/28 | Hindlimb ~day 29

Question 41

Describe hand development

Answer 41

Day 32- Flipper-like upper limb buds develop Day 35- hand plate forms Day 44- Digits begin to appear in the hand plate Day 45- Upper limbs bend at the elbow and the fingers are short and webbed Day 55- Fingers and toes are distinct and separated

Question 42

When does apoptosis occur in limb development?

Answer 42

When the webbing between the fingers disappears

Question 43

What are the two main genes that regulate limb development?

Answer 43

Fibroblast-like growth factor-8- Growth factor produced at the end of the developing limb Sonic hedgehog- Determines the overall structure of the limb that is developing

Question 44

What effect did thalidomide have on limb development?

Answer 44

Variably affected both sets of limbs but mainly upper limbs

Question 45

Which gender were affected more by thalidomide?

Answer 45

Boys

Question 46

What effect does fgf-10 have normally?

Answer 46

It normally has an effect in developing vasculature to the developing limb to provide nutrition

Question 47

How does thalidomide have an effect on limb development?

Answer 47

The active form hinders blood vessel development- there's a varying degree of cell death and limb development is prevented. Upper limbs are more susceptible to damage

Question 48

What does long term and short term exposure to thalidomide lead to?

Answer 48

Long exposure- widespread cell death and all signalling/cells lost Short exposure- Uniform cell death and only partial loss of signalling

Question 49

When was thalidomide usually taken?

Answer 49

Around 8 weeks PF when morning sickness was worst- this is a vital stage of limb development

Question 50

What is thalidomide commonly used to treat nowadays?

Answer 50

Leprosy especially in developing countries

Question 51

What is achondroplasia?

Answer 51

Form of dwarfism where long bones don't develop properly

Question 52

What causes achondroplasia?

Answer 52

Loss of function mutation in fibroblast growth factor receptor 3 which is usually involved in development and particularly elongation of bones