Embryology Part 2 Flashcards
What is the notochord?
Thickened region in mesoderm important in controlling specification of surrounding cells.
Signalling centre along centre
Important in development of nervous system
What is the Paraxial Mesoderm and what will it form?
Closest to the axis, where development of the vertebral column (notochord) point in the mesoderm.
Will form the somites which forms the Dorsal somites, leading to dermomyotome (dermis/muscles of back,) and Ventral/Medial Somites leading to the sclerotome (vertebrae and ribs)
What are the layers of the mesoderm moving from the notochord, laterally?
Notochord Paraxial Mesoderm Intermediate Mesoderm Lateral Plate Mesoderm Extraembryonic Mesoderm
What regions in the embryo do not contain mesoderm? What parts of the body will these regions form?
Oropharyngeal membrane (will develop to form mouth opening) Cloacal Membrane (will form anus) Don't require muscle for these areas, so pointless building up structures to break them down
How long does the formation of the 3 regions of mesoderm take?
4 days
What is the somite?
Building block of the muscle
What does the Intermediate Mesoderm form?
Genitourinary system
How does the Lateral Plate Mesoderm (and surrounding space) change with embryological development?
The LPM forms 2 layers which become split by the intraembryonic coelom.
The 2 layers are; Parietal aka somatic (superior) and Visceral aka splanchnic (inferior)
What germ layer forms the following smooth muscle components of the body- pupils, mammary, and sweat glands?
Ectoderm
What part of the body is formed from the Visceral (Splanchnic) Lateral plate mesoderm?
Gut and derivative smooth layers from the visceral layer surrounding the gut tube
Cardiac muscle from visceral layer surrounding heart tube
In what order, and when, does somite formation occur?
Form in pairs from head of embryo towards the tail end
Cranio-caudal sequence
Day 20 (weeks 3-5)
How is somitogenesis controlled?
Signals are turned on that help stimulate mesenchymal (loose cells) migration and tightening to epithelial like cells. This aids in the formation of the neural tube.
Notochord influences somite formation
Regulation via Notch, Wnt, and FGF
What genes control somitogenesis and how do levels of gene expression change during this process?
Notch- high levels initiate somite development, and then quickly decreases, moves head to tail
FGF8 Family- increase as notch decreases, moves tail to head
Wnt - Help process along
How do genes aid in somitogenesis?
They tell cells to switch between permissive and non-permissive state in constant timed fashion.
What happens to somites once they’ve formed?
They will go on to differentiate into the sclerotome (vertebrae and ribs) and dermomyotome (dermis and muscle of back)
When is somitogenesis complete, and how many pairs of somites are created?
Begins day 20, complete by end of 5th week
42-44 pairs
What is a somite?
Cells of paraxial mesoderm origin that help form the skeletal muscles and skeleton.
What happens to the somites once formed?
Starts to form different cell structure with cell proliferation
Start to differentiate
-> ventral/medial undergo epithelial to mesenchymal transition, forming sclerotome
-> dorsal cells form dermomyotome
What is the sclerotome?
Ventral somite cells that undergo epithelial to mesenchymal transitions (allowing them to migrate again)
Sclerotome helps form the vertebrae and ribs
What does the dermomyotome form?
Splits to form:
Dermatome- forms dermis of back
Myotome- forms muscles
What are the muscle cell precursors, and what stimulates the differentiation of the precursors into muscle cells?
Myoblasts
Myogenin stimulates differentiation of myoblasts into primary myotubes (they will align and fuse), and finally into myocytes (mature muscle cells)
MyoD and Myf5 are transcription factors that activate muscle specific genes and mediate differentiation of myoblast precursor cells into myoblasts.
What factors regulate the development of muscle during embryological development?
MYOD
MYF5
These transcription factors activate muscle-specific genes and enable differentiation of myogenic precursor cells in the dermomyotome into myoblasts
Where is MyoD (myoblast determination protein 1) found and how is it turned on?
Locally acting WNT proteins (activate) and BMP (inhibitory) will activate the MYOD at the edge of the dermomyotome.
MyoD and Myf5 enable differentiation of myogenic precursor cells in dermomyotomes into myoblasts.
How do you stimulate the formation of the dermatome from the dermomyotome?
The lateral plate mesoderm also produce WNT and BMP that can stimulate dermatome formation (as the WNT and BMP released from neural tube and notochord cannot move far enough to reach further parts of the dermomyotome)