Lecture 10 (Exam 2) Flashcards
This zone of mesoderm is a thick column closest to and parallel with the notochord. It becomes segmented into somites.
Paraxial mesoderm (segmental plate)
This zone of mesoderm is narrow column lateral to the paraxial mesoderm and gives rise to the urogenital system.
Intermediate mesoderm
This zone of mesoderm is a thin plate lateral to the intermediate mesoderm. It splits to form the lining of body cavities and mesoderm of most internal organs as well as limbs.
Lateral plate mesoderm
Remember that mesoderm originates from _______, passes through the primitive streak as _______ cells, spreads laterally, and establishes a continuous layer between ectoderm and endoderm.
Epiblast
Bottle
________ are initial pairs of segments of mesenchyme (barely discernible as segments) that begin to develop along and on either side of the neural plate in the paraxial mesoderm.
Somitomeres
New somitomeres are added (CRANIALLY/CAUDALLY) as the primitive steak regresses.
Caudally
After 20 pairs of somitomeres have formed (about day 20), the first pair of somites forms behind (caudal to) the ____ pair of somitomeres at the expense of the ____ pair of somitomeres.
7th
8th
________ are more dense, blocks of mesoderm that form along the notochord.
Somites
In a caudal direction, a pair of somitomeres is transformed into a pair of _______ every few hours.
Somites
As pairs of somites are formed, pairs of somitomeres are also formed at the (ANTERIOR/POSTERIOR) end of the primitive node.
Anterior
For each pair of somitomeres transformed into a pair of somites, a new pair of somitomeres is formed at the caudal end of the paraxial mesoderm. Because of this transformation and the formation of somites, _____ pairs of somitomeres are kept constant at the caudal end of the paraxial mesoderm.
11
Cells migrating through the primitive streak will form…
Cervical vertebrae
Thoracic vertebrae
Lumbar vertebrae
Cells migrating from the tail bud will form the…
Sacrum
Coccyx
There are ____ cranial somitomeres that will form most of the skeletal musculature of the head.
7
The history of a somite includes the following stages:
1) _______ stage
2) Epitheliomesenchymal transformation stage
3) Separation of _______
4) Breakup of epithelial dermatome into dermal _______
Epithelial
Myotome
Fibroblasts
In somite differentiation, this mechanism utilizes FGF-8, retinoic acid, and Mesp-2.
Wavefront mechanism
In the wavefront mechanism, increased _____ initiates mitosis in mesenchymal cells in the posterior primitive streak.
FGF-8
In the wavefront mechanism, increased ______ ______ more anteriorly opposes the action of FGF-8.
Retinoic acid
Note that the wavefront is also referred to as the determination front because there is a balance between FGF-8 and retinoic acid concentrations that results in cellular determination toward somitogenesis. ______ is important at this critical decision moment and is expressed because of the specific balance between FGF-8 and retinoic acid concentrations.
Mesp-2
This is the mechanism in somite differentiation that involves the roles oscillating expression of molecules in the Notch pathway (along with Wnt and FGF pathways) that leads to the establishment of the pattern for somite formation. This is expressed along a time line.
Segmentation clock
At each critical location that will serve to divide adjacent somites, ______ ______ will become concentrated at the future anterior border of a somite and ______ will be concentrated at the future posterior border of a somite.
Lunatic fringe
C-hairy
Cells at the anterior border of a somite express _____ (receptor) and cells of the posterior border of the anterior somite will express _____ (ligand), resulting in a fissure between the two adjacent somites.
Eph A
Eph B
Overlying ectoderm causes the expression of _____, which in turn causes the expression of ______ in the forming somite.
Wnt-6
Paraxis
_______ plus the down regulation of _______ results in the conversion of mesenchymal cells to epithelial cells. Then the somitocoel forms.
Paraxis
Snail
