Errors in First Aid for the USMLE (2007): Embryology

The following is from an email sent to the First Aid Team concerning errors/corrections/suggestions to their 2007 edition.

Embryology (reference: HY Embryo by Dudek)

  1. P.122, Embryological derivatives: Under neural crest cells, it lists “cranial nerves.” This is not true. Neural crest cells are responsible for the sensory ganglia of V, VII, IX and X and the parasympathetic ganglia of III, VII (ptery), VII (submand), IX and X. Motor ganglia of all cranial nerves come from the neuroectoderm of the neural tube. The remaining cranial nerve precursors: sensory ganglia of I (surface ectoderm), II (neuroectoderm), VIII (surface ectoderm for both vestibular and cochlear ganglia). Another way to display the CN origins:
    1. Surface ectoderm gives sensory for CN I and CN VIII (both cochlear and vestibular ganglia)
    2. Neuroectoderm gives sensory for CN II.
    3. Neuroectoderm gives motor ganglia for all cranial nerves (III, IV, V, VI, VII, IX, X)

                                                              i.            Sensory for CN II

    1. Neural Crest cells give parasympathetic ganglia for all cranial nerves (III, VII [pterygopalantine and submandibular], IX, X)
  1. P.122, Embryological derivatives
    1. It is mentioned that neural crest cells give rise to odontoblasts but not that they produce dentin . It should also be mentioned under ectoderm that ameloblasts produce the enamel.
  2. P.123, Twinning
    1. Monozygotic ( 65%), Dizygotic (fraternal) or monozygotic (35%).
  3. P.125, Fetal Circulation
    1. I’m sure someone has probably brought this up, but the shading for this diagram is inaccurate. It shows the umbilical vein as carrying less oxygenated blood from the mother to the fetus and more oxygenated blood carried in the umbilical arteries from the fetus to the mother. The fetal circulation cannot be divided into left and right as it can be in the adult (and is in this diagram). The order of oxygenation should be as follows (and represented graphically with gradient shading instead of gray v. white: from most to least

                                                              i.            Most oxygenated blood from L. umbilical vein to end of Ductus venosum

                                                            ii.            Mixing of blood with return from IVC (where it meets ductus venosum) to R. atrium

                                                          iii.            More oxygenated blood following along strong arrow, entering the L. ventricle without much mixing in the R. atrium and R. ventricle with less oxygenated blood from the SVC.

                                                          iv.            Medium oxygenated blood delivered straight to arch of aorta, leaving through R. and L. subclavian aa, L. coronary.

                                                            v.            Less oxygenated blood returning from head into SVC, entering R. ventricle without much mixing with more oxygenated blood from the IVC followed by ejection into Pulmonary trunk through Ductus Arteriosis and into thoracic aorta.

                                                          vi.            Least oxygenated blood leaving via R. and L. umbilical aa.

  1. P.127, Ear development
    1. Eardrum” should be replaced with “tympanic membrane.”
  2. P.128, Cleft lip and cleft palate
    1. In describing the cleft palate, “failure of fusion of the lateral palatine processes, the nasal septum, and/or the median palatine process (formation of [secondary] palate).” I found the bold part very confusing. After describing the primary palate with relation to a cleft lip, why is the term ” median palatine process” used instead of the already introduced “primary palate?” I think that this should be changed, with “primary palate” used instead.
  3. P.128, Diaphragm embryology
    1. I think that the adult derivatives of each part of the diaphragm could be mentioned along with special mention that congenital hiatal hernias are more often through the L. pleuroperitoneal membrane.

                                                              i.            Septum transversum (central tendon)

                                                            ii.            Pleuroperitoneal folds (muscle)

                                                          iii.            Body wall ( muscle)

                                                          iv.            Dorsal mesentery of the esophagus (crura)

  1. P.129, Genital ducts
    1. I suggest adding the following:

                                                              i.            “Mullerian inhibiting hormone (MIH) secreted by the Sertoli cells of the testes suppresses development of the paramesonephric ducts in males. [Up arrow] androgens secreted by the Leydig cells cause development of the mesonephric ducts.”

Return to First Aid Errors page.


4 Responses to Errors in First Aid for the USMLE (2007): Embryology

  1. SM says:

    Entry 1…Point 1…the sentence that says “surface…ganglia)”…I think you meant to say CN I instead of CN II.

  2. Thanks SM for the catch. I’ve corrected the entry (so if you’re seeing this for the first time, you won’t know what we’re talking about).

  3. violondrina says:

    shouldn’t the LEAST oxygenated fetal blood be the return from the IVC (before the ductus v.), the SVC, portal vein, and pulm. aa’s before they reach the heart? the umbilical aa’s are carrying mixed blood since they are coming off the aorta and the blood hasn’t gone to the tissues yet.

    what do you think?

  4. prettypreeti says:

    first aid says that alpha-fetoprotein levels are increased in amniotic fluid of down’s syndrome fetuses.

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