Embryology - 1st Lecture Flashcards
What is fertilisation?
A single fertilised egg that fuses 2 nuclei to form a zygote
What period is the first 8 weeks of development known as?
Embryonic period
What occurs at the end of week 3?
Fertilisation
What occurs between weeks 4 and 8?
Embryonic development
What occurs between week 9 and birth?
A foetus develops and matures
What is gametogenesis?
The creation of gametes (oocyte and spermatozoa)
What is cleavage?
A period of rapid cell division to form the morula and then the blastocyst
Where does cleavage occur?
In the coat of the oocyte
What is a morula? (googles definition)
16 cells (a solid ball of cells resulting from division of a fertilised ovum, and from which a blastocyst is formed)
What is a blastocyst?
More than 16 cells; a further development of a morula that implants into uterine wall
How many layers does a blastocyst have?
2; one on the inside and one on the outside
Over how many days does the formation of the blastocyst occur?
4 days
What is gastrulation?
The formation of the germ layers
What week of development does gastrulation occur?
Week 3
Name the 3 germ layers
Endoderm, ectoderm, mesoderm
What else occurs during gastrulation?
The body axes are establishes
How does the formation of the body plan come about?
Due to embryonic folding (tube-within-a-tube)
What week does the formation of the body plan occur?
Week 4
What 2 tubes are involved in embryonic folding in establishing the body plan?
Gut tube and skin/body wall
What is organogenesis?
The formation of organs and organ systems
Describe what occurs during the foetal period
Growth and weight gain; tissues mature and become function; overt sexual differentiation; ossification; connections are made in the CNS
Describe early stage abnormalities
Easily overcome/very rare as embryo can solve problem early or loss of embryo
Describe embryonic stage abnormalities
More common as more division occurs so something can be missed
Describe foetal stage abnormalities
Abnormalities of the function of organs rather than the development of organs
List the 4 primary processes (1)
Cell division; differentitiation; cell attachment; apoptosis
Describe differentiation as a primary process
There is specialisation and change in appearance as well as adoption of new functions
Describe cell attachment as a primary process
Physical/functional linkages are created and there is the formation of tissues
Describe apoptosis as a primary process
Removes cells that have served their function in a controlled way and interwebbing between cells is removed
Name the 2 primary processes (2)
Induction; cell migration
Describe induction as a primary process
The ability of one cell type to cause another to differentiate by responding to a signal depending on where they are
Describe cell migration as a primary process
Movement of cells from one location to another
List the 3 secondary processes
Axis formation/polarity; folding/rotation; increase/decrease in mass
Describe axis formation/polarity as a secondary process
Allows cells to understand where they are relative to the body axis
Describe folding/rotation as a secondary process
Entire embryo or structures within it fold - important in the folding of the heart
Describe increase/decrease in mass as a secondary process
Mass either compacts or expands
Describe hypertrophy
Individual cells get larger resulting in a larger structure
Describe hyperplasia
Increase in size due to increase in number of cells
What does the sperm contribute to the zygote?
Only DNA
What does the oocyte contribute to the zygote?
Cytoplasm, DNA, protein, rRNA
What drives development?
Maternal rRNA
What takes over the regulatory site?
The embryo once it begins transcribing its own genes
Describe genetic imprinting?
During gametogenesis, DNA has a pattern of methylation which means it is packaged in a specific way so certain genes are exposed, depends on maternal or parental contribution to see what genes are exposed
How are Angleman Syndrome and Prader-Willi Syndrome different?
The same region of chromosome is deleted but they differ depending on whether it is a paternal or maternal chromosome that has been cut
