Embryology and Evolution
The parathyroid glands originate from the interaction of neural crest mesenchyme and third and fourth branchial pouch endoderm.
Eya-1 (transcripitonal co-activator), Six-1 (a homeobox transcription factor), and Gcm-2 (a transcription factor) have been associated with the development of the parathyroid gland, and alterations in these genes alters parathyroid gland development.
The superior parathyroids arise from the fourth pharyngeal pouch, and the inferior parathyroids arise from the third pharyngeal pouch. They are vertically transposed during embryogenesis. This is significant in function-preserving parathyroidectomy, because both the superior and the inferior parathyroids are supplied by the inferior thyroid artery. If the surgeon is to leave a single functional parathyroid for the patient, he/she must preserve the appropriate blood supply.
Read more about this topic: Parathyroid Gland
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“Historians will have to face the fact that natural selection determined the evolution of cultures in the same manner as it did that of species.”
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