Phases Of Early Development

Question 1

What occurs in the pre-organogenesis phase? (3)

Answer 1

Cell division
Polarisation of the embryo
Formation of two layers (bilaminar germ disc)

Question 2

What happens in the embryo phase? (3)

Answer 2

• Gastrulation
• Laying down of basic body plan
• organogenesis

Question 3

What is gastrulation?

Answer 3

The blastula (single layered) is reorganised into a multilayered gastrula

Question 4

What happens in the fetus phase? (3)

Answer 4

Growth
Refinement
Function

Question 5

What is an oocyte?

Answer 5

Female sex cell that hasn’t undergone meiosis

Question 6

What is an ovum?

Answer 6

A mature female sex cell

Question 7

What is a morula?

Answer 7

A ball of cells resulting from hyperplasia of the zygote. The cell remains the same size

Question 8

What is a zygote?

Answer 8

A fertilised ovum. It has both sets of nuclei

Question 9

What is compaction?

Answer 9

When the morula compacts into a tight ball of cells

Question 10

What is a blastomere?

Answer 10

A cell that makes up the morula

Question 11

What is a blastocyst?

Answer 11

A hollow ball of cells with a thickening at one end

Question 12

What is a blastocoel?

Answer 12

The fluid inside the blastocyst

Question 13

List the phases of zygote division

Answer 13

Zygote-two stage cell- four stage cell- morula(8)-blastocyst-loss of zona pellucida

Question 14

What are the two components of a blastocyst?

Answer 14

Trophoblast and embryoblast

Question 15

The inner cell mass of the blastocyst separates into two layers. Name the layers

Answer 15

Epiblast and hypoblast

Question 16

What will the epiblast form?

Answer 16

The embryonic tissue

Question 17

What will the hypoblast form?

Answer 17

Embryonic tissues

Question 18

What do the extra-embryonic membranes do/provide?

Answer 18

Nourishment
Protection
Waste disposal

Question 19

What do the extraembryonic membranes consist of? (4)

Answer 19

Amnion
Allantois
Chorion
Placenta

Question 20

What is the amnion?

Answer 20

It protects the embryo allowing it to float

Question 21

What is the allantois for?

Answer 21

Fetal waste disposal

Question 22

What does the chorion do?

Answer 22

It contains the blood vessels for exchange with the external environment

Question 23

What is the placenta and what is it formed from?

Answer 23

It is an organ that contains maternal and fetal blood vessels. It is made from the cytotrophoblast and the syncytiotrophoblast

Question 24

What week does preorganogenesis happen?

Answer 24

0-2

Question 25

What weeks does the embryonic phase occur?

Answer 25

3-8 weeks

Question 26

What weeks does the fetal phase occur?

Answer 26

9-38

Question 27

Gastrulation forms three body layers, name these

Answer 27

Ectoderm Mesoderm Endoderm

Question 28

Which layer is the ectoderm and what will it form?

Answer 28

Outer layer | Skin and nervous system

Question 29

What layer is the mesoderm and what will it form?

Answer 29

Middle layer | Internal organs and chorion

Question 30

What layer is the endoderm and what will it form?

Answer 30

Inner layer | Internal linings

Question 31

At how many days does Gastrulation occur?

Answer 31

12-15

Question 32

At how many days post fertilisation is the embryo not allowed to be used?

Answer 32

14

Question 33

What is the primitive streak?

Answer 33

Is the first thing to form in Gastrulation, it is on the surface of the epiblast-a line at one end. At the end the primitive node forms

Question 34

What is invagination?

Answer 34

The cells of the epiblast migrate to the primitive streak and slip beneath it via the node

Question 35

How are the three layers formed by invagination?

Answer 35

The cells move and displace the hypoblast

Question 36

What is the germ layer?

Answer 36

The ectoderm

Question 37

What is a key part formed by Gastrulation?

Answer 37

Gut formation

Question 38

What layer rolls and pinches off forming the gut?

Answer 38

The endoderm

Question 39

What would happen if there were problems with the Gastrulation phase?

Answer 39

Pregnancy would normally terminate

Question 40

What is the disorder situs inversus?

Answer 40

Where the position of the internal organs are reversed

Question 41

What is situs ambiguous disorder?

Answer 41

Where so,e of the internal organs are displaced

Question 42

What is a sacrococcygeal teratomas?

Answer 42

A tumour in baby which has all three layers of Gastrulation, often highly vascularised