Embryology

Question 1

From when till when is the pregnancy considered an embryo?

Answer 1

Week 3 - week 8

Question 2

From what point is the pregnancy classified as a foetus?

Answer 2

Week 9 and onwards

Question 3

Name the process that happens during the embryonic period.

Answer 3

Organogenesis

Question 4

What is the definition of embryology?

Answer 4

The study of initial development of an embryo

Question 5

All organ systems are developed (rudimentary forms) by what week?

Answer 5

Week 8

Question 6

What period follows the embryonic period?

Answer 6

The foetal period

Question 7

After fertilisation of the egg cell what can we call the new cell?

Answer 7

A zygote

Question 8

What is the name given to the division of the early embryo?

Answer 8

Cleavage

Question 9

After three days of cleavage of the zygote what is the embryo now referred to as?

Answer 9

A morula

Question 10

By day four what is the embryo referred to as?

Answer 10

A blastocoele has developed and the embryo is now seen as a blastocyst

Question 11

At day five what is the name given to the embryo?

Answer 11

An embryoblast

Question 12

Which cells will form the placenta?

Answer 12

Trophoblast cells
They are the outer ring of cells

Question 13

Where does gastrulation occur?

Answer 13

The germinal disc

Question 14

What is gastrulation?

Answer 14

The generation of three germ layers which derive all embryonic structures.

Question 15

What happens during days 6/7?

Answer 15

Hatching occurs from the zona pellucida

Question 16

What happens during days 8/9?

Answer 16

Blastocyst implantation

Question 17

How is the amniotic cavity and yolk sac formed?

Answer 17

Hypoblast and epiblast cells divide, growing two lumens

Question 18

What is the bilaminar germinal disc?

Answer 18

The interface of two cell types
It becomes the foetus

Question 19

In what direction does gastrulation occur?

Answer 19

Along the primitive streak in a caudal to cranial orientation

Question 20

What are the three germ layers?

Answer 20

Ectoderm (epiblast)
Mesoderm
Endoderm (hypoblast)

Question 21

Is the yolk sac in mammals important?

Answer 21

It serves some function but is not as important in mammals as it is for species who lay eggs whose offspring do not have a placenta attached to the mother

Question 22

What is the ectoderm responsible for forming?

Answer 22

Epidermis of the skin
Nervous system
Sensory receptors of epidermis
Epithelial lining of mouth and anus

Question 23

What structures is the mesoderm responsible for forming?

Answer 23

The notochord
Skeletal muscle
Muscular layer of the stomach and intestines
Circulatory and lymphatic systems
Reproductive systems
Dermis if skin

Question 24

What structures is the endoderm responsible for forming?

Answer 24

Epithelial lining of the digestive tract and the respiratory system
Lining of the urethra, urinary and reproductive systems
Liver
Pancreas
Thyroid and parathyroid glands

Question 25

Why is the notochord important?

Answer 25

In vertebrates it’s transient and organises surrounding tissues and provides structural support.

Question 26

What did the notochord regulate?

Answer 26

Left/ right asymmetry Arterial/ venous identity in major vessels Aids in specification of forming somites

Question 27

Describe how the neural tube is formed.

Answer 27

The notochord will influence the tissue above it to develop into the neural tube, the tube is pinched off and is a true tube now, while the mesoderm not influenced by the notochord will develop into skin.

Question 28

How are the neural groove and neural folds formed?

Answer 28

Uneven proliferation

Question 29

What are neuro pores? Where are they?

Answer 29

The openings of the neural tube, there are cranial and caudal neuro pores which are the last areas of the neural tube to close.

Question 30

What is a morphogen and what does it do?

Answer 30

It is a growth factor and it influences cells to change their activity, It can be very potent, depending on its concentration gradient (if low if can influence one way, if high it may influence a different way)

Question 31

How do different morphogen interact with each other?

Answer 31

They can influence the cells differently to how would have done separately They not act complimentary, they may compete or cancel each other out

Question 32

What is cell competence?

Answer 32

Whether the cell can react properly to the signal and influence being expressed on it

Question 33

What is Sonic Hedgehog factor?

Answer 33

It is a very powerful morphogen released by the notochord to induce the neural plate Changes ectodermal tissue into neural tissues

Question 34

What other morphogen work with SHH?

Answer 34

Chordin and noggin These are expressed in the node at the cranial end of the primitive streak

Question 35

What does it mean to set the midline of the embryo?

Answer 35

Morphogens are key for this as they help to determine dorsal/ ventral and left/ right axes bit of which are required for future brain segmentation

Question 36

What are neural crest cells?

Answer 36

These are neural tissue cells that can migrate from the CNS to the rest of the embryo which can give rise to the adrenal medulla and melanocytes Defect can occur due to lack of migration or folding of crest cells

Question 37

Where are neural crest cells found?

Answer 37

They detach from the neural folds and sit dorsal to the roof plate of the neural tube