Mesoderm Quiz

From Embryology
Here are a few simple questions that relate to mesoderm development. Take the quiz and see what you know, if you get some wrong, try working through through the embryology Mesoderm Lecture before you try this quiz.

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1. Mesenchyme refers to the middle layer of the trilaminar embryo


The the middle layer of the trilaminar embryo is the mesoderm (meaning middle layer), while most of these cells are mesemchymal in appearance, this term is used to describe the cell histological appearance/organization.

2. The intraembryonic coelom forms within :

  lateral plate
  neural tube
  intermediate mesoderm

The intraembryonic coelom forms initially small spaces in the mesoderm layer and coalesce to form a single large "horseshoe-shaped" space within the lateral plate mesoderm around the embryonic disc. Both young somites (somitocoels) and the neural tube (neural tube lumen) do have cavities, but neither is called the intraembryonic coelom. Note that in early development the intraembryonic coelom opens at places on the edge of the embryonic disc to the extraembryonic coelom.

3. Somites are developmental structures that contribute the following adult structures :

  vertebra, notochord, dermis, skeletal muscle
  vertebra, intervertebral discs, dermis, skeletal muscle
  kidney, body wall connective tissue, sensory ganglia
  kidney, gastrointestinal tract smooth muscle, mesentery

Each somite has specific regions that contribute different components of the embryo. Sclerotome contributes the vertebral column (vertebra, intervertebral discs). Dermotome contributes the connective tissue layers of the skin (dermis, hypodermis). Myotome ontributes the skeletal muscle of the body and limbs.

4. All paraxial mesoderm segments into somites.


While somites do form within paraxial mesoderm, this region remains unsegmented at the level of the head and therefore does not incorporate into somites.

5. Which of the following statements about somites is/are correct:

  Differentiate a covering epithelium in their early stages.
  Somites contribute the body wall osteogenic, chrondrogenic and fibrogenic cells.
  Contribute to a single vertebral level body and the intervertebral disc.
  Myotomes contribute the smooth muscle associated with the gastrointestinal tract wall.

Paraxial mesoderm forming the early somite does initially form a transient epithelial layer that covers each somite. This layer breakdown with later development, allowing the somite components to disperse. The sclerotome component of each somite pair engulf the left and right side of the notochord forming the entire axial column, that includes the vertebra and intervertebral disc (from each somite). Somatic not somitic mesoderm forms the body wall osteogenic, chrondrogenic and fibrogenic cells. Don't mix up somatic/somitic. You may have had to think about this as the dermatome, forming the dermis and fibrogenic cells, does mix with somatic mesoderm later in development, but does not contribute either osteogenic or chrondrogenic cells. Myotomes contribute the skeletal muscle not smooth muscle. The GIT smooth muscle comes from splanchnic mesoderm.

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