Which places the developing heart in the presumptive thoraci

Discussion in 'USMLE STEP 1' started by Guest, Jan 9, 2010.

  1. Guest

    Guest Guest

    Which places the developing heart in the presumptive thoracic region cranial to the septum transversum?
    A. Gastrulation
    B. Lateral folding
    C. Cranial folding
    D. Neurulation
    E. Fusion of the endocardial heart tubes
  2. Guest

    Guest Guest

    The answer is: C

    Initially, the developing cranial portion of the neural tube lies dorsal and caudal to the oropharyngeal membrane. However, overgrowth of the forebrain causes it to extend past the oropharyngeal membrane and overhang the cardiogenic area. Subsequent growth of the forebrain pushes the developing heart ventrally and caudally to a position in the presumptive thoracic region caudal to the oropharyngeal membrane and cranial to the septum transversum that will form the central tendon of the diaphragm. Gastrulation is the process by which epiblast cells migrate to the primitive streak and become internalized to form the mesodermal and endodermal germ layers. Neurulation refers to formation of the neural tube from surface ectoderm. Lateral folding of the embryo forms the endoderm tube and surrounding concentric layering of mesoderm and ectoderm

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