Embryology (from week 3 to week 8) Flashcards
Describe what occurs at week 3, when gastrulation starts
In gastrulation, the primitive streak and primitive node forms in the epiblast
What is the function of the anterior visceral endoderm?
It determines the node and tail ends of the embryo
In gastulation, what events occur at the streak and node?
The cells in the primative streak start to divide and migrate away from the epiblast and start to replace the cells in the hypoblast. This forms the endoderm.
In gastrulation, how does the notochord from, what is it and what is its specialised feature?
It is a specalised mesoderm signalling structure that forms from migrating epiblast cells that travel in front of the primative node in between the two layers. It also defines ventral axis.
In gastrulation, how does the mesoderm form?
When migrating cells from the epiblast spread between the two layers
How does neural tissue form?
Skin usually forms from the ectoderm in the presence of bone morphogentic protein (BMP). However the notochord releases factors such as chordin, noggin and follistatin which blocks BMP and causes the ectoderm to form neural tissue
What happens to the neural plate in neurulation?
The cells start to thicken and the epithelial cells become columnar and curve. They then form the neural groove. The edges of the neural tube come together and fuse at the cervical region
What are the two ends of the tubes that need fused and if unfused can lead to what defects?
The rostral neuropore (if unfused leads to anencephaly) and the caudal neuropore (forms of spinal bifida).
What is neurulation?
The formation of the neural tube
How do neural crest cells form?
They undergo EMT (epithelial to mesenchymal cell transition) and migrate throughout the embryo
Name the wide variety of cells that form from neural crest cells, give some specific examples
Neurons and glia, Cartilage and bone, Connective tissue, Pigment cells, sensory neurons and glia, sympathoadrenal cells
Cranial nerve ganglia Dorsal root ganglia Autonomic ganglia Adrenal medulla Schwann cells Peripheral glial Odontoblasts Thyroid parafollicular cells melanocytes
Name two diseases that arise from neural crest defects
Waardenburg’s syndrome
Treacher Collins syndrome
Describe the different layers the mesoderm cells form
Paraxial layer
Intermediate layer
Lateral plate layer
Where do the endoderm, mesoderm and ectoderm arise from?
Cells migrate and replace hypoblast cells in the hypoblast and this forms the endoderm
The cells that are in the two layers form the mesoderm
The cells that remain in the epiblast form the ectoderm
What does the paraxial mesoderm layer form?
They form segments called somites
describe somite formation
Cells have a timer along the paraxial mesoderm and they go through cycles every 90 minutes which is defined by notch signalling clock. There is a wave of FGF signal that passes along the embryo which causes the cells to change into part of a somite.
If the wave passes cells early in the cycle then they become the front end of the somite. If the wave passes cells later on in their cycle then they become the tail end of the somites.
What is the homobox genes
A gene sequences that regulates the formation of body structures in the correct place.
What are some of the derivatives of mesoderm
Pariaxial mesoderm - sclerotome (bone and cartilage), Myotome (muscle) and Dermatome (skin associated) Which are all derived from somites
Midline mesoderm - forms notochord
Intermediate mesoderm - forms kidneys and gonads
Lateral plate mesoderm - forms splanchnic (viscera and CVS) and somatic (body wall)
Name some of the ectoderm derivatives
Epidermis Lens and retina Olfactory epithelium Oral cavity epithelium Sensory organ of the ear Glands Adenohypophysis
Name some of the endoderm derivatives
The yolk sac closes off to form a the gut tube. Buds come off of the tube to form organs. (organs and GI)
What is gastrulation?
Process by which the blastula forms into a grastula (multilayered disk)
