Early Embryology 2 Flashcards
What are the 4 key processes after fertilisation and before implantation?
- Gastrulation
- Neurulation
- Segmentation and Folding
What causes the epiblast layer to differentiate into a trilaminar disc?
The epiblasts multiply and move towards the primitive streak
What are the 3 layers of the trilaminar disc?
- Ectoderm
- Mesoderm
- Endoderm
What is Situs Invertus?
The organs are back to front due to defective side-specific signalling cascades
What is formed in the middle of the mesoderm in week 4 and what is its purpose?
Notochord which is a solid rod of cells with an important signalling role
What do notochord signals initiate?
Causes the ectoderm to thicken
What is formed when the neural plate lifts and curls and what causes it?
Thickening of the ectoderm causes the neural plate to form the neural tube and the ectoderm closes around it
State the 4 types of differentiated mesoderm
- Intermediate mesoderm
- Somatic mesoderm
- Splanchnic mesoderm
- Paraxial mesoderm
What is the name of the space between the somatic and splanchnic mesoderm?
Intraembryonic Coelom
Name the 3 derivatives of somites and what they ultimately become
- Dermatome becomes skin
- Myotome becomes muscles
- Sclerotome becomes bones
What does the organisation of the mesoderm into somites give rise to? Give an example
- Repeating Structure
- E.g. Vertebrae, Ribs
How many segments are formed in segmentation and what do they represent?
31 pairs that form spinal nerves
What is the name of head and tail folding?
Cephalocaudal
Why does folding occur?
To ensure bodily systems and features are in the correct place
What does lateral folding result in?
Only the ectoderm being visible
State 3 consequences of folding
- Brings pericardial sac to the correct position
- Draws together disc margins to create umbilicus
- Amniotic membrane is pulled around the disc
- Embryo becomes suspended within the amniotic sac
- Connecting stalk (umbilical cord) pulled ventrally
- Formation of chorionic cavity
What has occurred at the end of the 4th week of pregnancy?
- Nervous system has started to form
- Segments assign specific tasks to specific cells
What does the Intraembryonic Coelomeventually become?
Thoracic and abdominal cavities
Give one derivative of the paraxial mesoderm
Skeletal muscle cells
What does the intermediate mesoderm give rise to?
Urogenital system
What does the somatic mesoderm form?
Bones, ligaments, blood vessels
What does the splanchnic mesoderm become?
The heart and visceral layers
