BL Embryology

Question 1

What are the 5 key steps of embryonic development?

Answer 1

1- fertilisation + implantation
2- gastrulation
3- neurulation
4- segmentation
5- folding

Question 2

When is the pre-embryonic period?

Answer 2

First 2 weeks

Question 3

When is the embryonic period?

Answer 3

3-8 weeks

Question 4

When is the foetal period?

Answer 4

9-38 weeks

Question 5

Total period of gestation

Answer 5

38 weeks +/- 2

Question 6

What is the length of a clinical pregnancy?

Answer 6

40 weeks?

Question 7

What are the stages of the pre-embryonic period?

Answer 7

1- fertilisation
2- cleavage
3-compaction
4- hatching
5- implantation

Question 8

Describe fertilisation

Answer 8

1- oocyte released from ovary
2- travels along fallopian tube under action of progesterone
3- sperm fertilised in ampulla
4- zygote formed

Question 9

What is a zygote?

Answer 9

Fertilised oocyte

Question 10

Where does fertilisation occur?

Answer 10

Ampulla of fallopian tube

Question 11

Where is the ideal site for implantation?

Answer 11

Posterior uterine wall

Question 12

What is a morula?

Answer 12

Solid ball of cells from a zygote

Question 13

What is cleavage?

Answer 13

First division of zygote resulting in 2 blastomeres surrounded by Zona pellucida

Initiates a series of mitotic cell division which forms a morula

Question 14

What is compaction?

Answer 14

Formation of a blastocyst

Question 15

What is pre-implantation genetic diagnosis?

Answer 15

When a cell is safety removed from morula to be tested for serious hereditary conditions

Done before implantation of embryo in IVF

Question 16

What happens in week 1?

Answer 16

1- cleavage
2- compaction
3- hatching

Question 17

What is Zona pellucida?

Answer 17

Thick glycoproteins shell which surrounds blastomeres + protects from sperm after fertilisation

Question 18

What is hatching?

Answer 18

Blastocyst leaves Zona pellucida + can interact with uterine surface to implant

Question 19

Describe a blastocyst

Answer 19

Inner cell mass (embryoblast)
Outer cell mass (trophoblast)
Zona pellucida surrounding
Blastocyst cavity

Question 20

What will the embryoblast develop into?

Answer 20

Embryo

Question 21

What is a trophoblast?

Answer 21

Cells forming the outer layer of blastocyst that provide stability to blastocyst

Question 22

What type of stem cells are before and after compaction?

Answer 22

Before - Totipotent
After - pluripotent

Question 23

Why is week 2 called the week of twos?

Answer 23

Trophoblast splits into - syncytiotrophoblast
- cytotrophoblast
Embryoblast forms bilaminar disc - epiblast
- hypoblast

Question 24

What provides O2 and nutrient to growing embryo?

Answer 24

Maternal blood

Question 25

What does the hypoblast do?

Answer 25

Lines the yolk sac

Question 26

What is the result of early embryonic period?

Answer 26

Foundations for development of body systems

Question 27

What is needed in the early embryonic period?

Answer 27

Sufficient cells of right type in the right place

Question 28

What happens in gastrulation?

Answer 28

Bilaminar disk >> trilaminar disk Forms three germ layer - ectoderm, mesoderm + endoderm

Question 29

Why does gastrulation occur?

Answer 29

To ensure correct placement of tissues to allow subsequent morphogenesis to occur

Question 30

When does gastrulation occur?

Answer 30

Week 3 Embryonic period

Question 31

How does gastrulation occur?

Answer 31

- Primitive streak forms in caudal epiblast - migration + invagination of epiblast cells - bilaminar disk >> trilaminar disk

Question 32

What does the ectoderm derive into?

Answer 32

Organs+ structures that maintain contact with outside world *e.g. nervous system, epidermis*

Question 33

Where does the nervous system arise from?

Answer 33

Ectoderm

Question 34

What does the mesoderm derive into?

Answer 34

Supporting tissues *e.g. muscles, cartilage, bone, vascular system*

Question 35

What does the heart arise from?

Answer 35

Mesoderm

Question 36

What does the endoderm derive into?

Answer 36

Internal structures *e.g. epithelial lining of GI tract, respiratory tract, parenchyma of glands

Question 37

What are the types of mesoderm?

Answer 37

Somatic Splanchnic Paraxial Intermediate

Question 38

Where do somites arise form?

Answer 38

Paraxial mesoderm

Question 39

What are the somites derivatives and what do they form?

Answer 39

Dermatome >> dermis Myotome >> muscles Sclerotome >> hard tissue, bone

Question 40

What does folding achieve?

Answer 40

Draw together margins of disk - creates ventral body wall - pulls amniotic membrane around disk - pulls connecting stalk centrally Puts heart + diaphragm in right place Creates new cavity within embryo

Question 41

What occurs after 4 weeks?

Answer 41

Nervous system forming Embryo folded >> everything in correct place Segments appeared >> cells have specific tasks

Question 42

Describe neurulation

Answer 42

- Notochord releases signals - overlying ectoderm thickens > neuroectoderm - mesoderm becomes Paraxial, intermediate, somatic or splanchnic mesoderm

Question 43

Describe folding of embryo

Answer 43

Cephalcaudal Head folds Tail folds Lateral folding Forms primitive gut + amniotic sac

Question 44

How does the neural tube form?

Answer 44

The neural plate forms paired neural folds that unite

Question 45

How does the neural plate form?

Answer 45

Notochord induced thickening on the overlying ectoderm

Question 46

How are holes left available for mouth and anus?

Answer 46

Gaps in mesoderm on trilaminar disc allow for holes to not be closed up

Question 47

What does the neural tube become?

Answer 47

Central nervous system

Question 48

What is the primitive streak?

Answer 48

Thin depression on the surface of ectoderm

Question 49

What does the trophoblast split into?

Answer 49

Cytotrophoblast Syncytiotrophoblast

Question 50

What does the embryoblast split into?

Answer 50

Epiblast Hypoblast

Question 51

What is morphogensis?

Answer 51

Development of form and structure

Question 52

Describe how the intraembryonic coelom is formed?

Answer 52

Splanchnic folds down + towards itself, meeting in the middle + jointing Somatic layer folds down (lower than splanchnic layer) joining with itself, leaving a cavity This cavity i the intraembryonic coelom