Phases Of Early Development Flashcards
What occurs in the pre-organogenesis phase? (3)
Cell division
Polarisation of the embryo
Formation of two layers (bilaminar germ disc)
What happens in the embryo phase? (3)
- Gastrulation
- Laying down of basic body plan
- organogenesis
What is gastrulation?
The blastula (single layered) is reorganised into a multilayered gastrula
What happens in the fetus phase? (3)
Growth
Refinement
Function
What is an oocyte?
Female sex cell that hasn’t undergone meiosis
What is an ovum?
A mature female sex cell
What is a morula?
A ball of cells resulting from hyperplasia of the zygote. The cell remains the same size
What is a zygote?
A fertilised ovum. It has both sets of nuclei
What is compaction?
When the morula compacts into a tight ball of cells
What is a blastomere?
A cell that makes up the morula
What is a blastocyst?
A hollow ball of cells with a thickening at one end
What is a blastocoel?
The fluid inside the blastocyst
List the phases of zygote division
Zygote-two stage cell- four stage cell- morula(8)-blastocyst-loss of zona pellucida
What are the two components of a blastocyst?
Trophoblast and embryoblast
The inner cell mass of the blastocyst separates into two layers. Name the layers
Epiblast and hypoblast
What will the epiblast form?
The embryonic tissue
What will the hypoblast form?
Embryonic tissues
What do the extra-embryonic membranes do/provide?
Nourishment
Protection
Waste disposal
What do the extraembryonic membranes consist of? (4)
Amnion
Allantois
Chorion
Placenta
What is the amnion?
It protects the embryo allowing it to float
What is the allantois for?
Fetal waste disposal
What does the chorion do?
It contains the blood vessels for exchange with the external environment
What is the placenta and what is it formed from?
It is an organ that contains maternal and fetal blood vessels. It is made from the cytotrophoblast and the syncytiotrophoblast
What week does preorganogenesis happen?
0-2
What weeks does the embryonic phase occur?
3-8 weeks
What weeks does the fetal phase occur?
9-38
Gastrulation forms three body layers, name these
Ectoderm
Mesoderm
Endoderm
Which layer is the ectoderm and what will it form?
Outer layer
Skin and nervous system
What layer is the mesoderm and what will it form?
Middle layer
Internal organs and chorion
What layer is the endoderm and what will it form?
Inner layer
Internal linings
At how many days does Gastrulation occur?
12-15
At how many days post fertilisation is the embryo not allowed to be used?
14
What is the primitive streak?
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
What is invagination?
The cells of the epiblast migrate to the primitive streak and slip beneath it via the node
How are the three layers formed by invagination?
The cells move and displace the hypoblast
What is the germ layer?
The ectoderm
What is a key part formed by Gastrulation?
Gut formation
What layer rolls and pinches off forming the gut?
The endoderm
What would happen if there were problems with the Gastrulation phase?
Pregnancy would normally terminate
What is the disorder situs inversus?
Where the position of the internal organs are reversed
What is situs ambiguous disorder?
Where so,e of the internal organs are displaced
What is a sacrococcygeal teratomas?
A tumour in baby which has all three layers of Gastrulation, often highly vascularised
