MCQ Anatomy Answer 47

The correct answer is C.

Explanation:

The primitive streak is the region of the epiblast through which the cells that give rise to the notochord and the mesoderm of the embryo pass. The only adult derivative of the notochord is the nucleus pulposus of the intervertebral disk. The mesoderm gives rise to many different tissue types including muscle, connective tissue, and blood. This accounts for the many different tissue types found in a sacrococcygeal teratoma.

The dorsal root ganglia (choice A) are derived from neural crest cells. The neural crest develops at the time of neurulation, which is a process of infolding of the neural ectoderm that is induced by the notochord.

The lining of the gastrointestinal tract (choice B) is derived from endoderm. The endoderm also gives rise to evaginations of the gastrointestinal tract, such as the liver and pancreas. The smooth muscle and connective tissue of the gastrointestinal tract are derived from mesoderm.

The spinal cord (choice D) is derived from neural ectoderm, which invaginates during neurulation to form the neural tube. The caudal part of the neural tube forms the spinal cord, and the rostral part of the neural tube forms the brain.

The thyroid gland (choice E) is derived from endoderm. The endoderm of the floor of the pharynx evaginates to form the thyroglossal duct, which descends to form the thyroid gland. The adult site of the evagination of the thyroglossal duct is marked by the foramen cecum on the tongue.

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