Morphology and relationships of ultimobranchial body with pharyngeal pouches

ABSTRACT

The ultimobranchial body in humans is still controversial and different theories have been put forward. The aim of this study was to clarify the topographical anatomy of the ultimobranchial body and surrounding tissue during early development. Human embryos at 5-7 weeks of development were used for morphological observation. During the early stages, the sections displayed a ladder-like arrangement of the second to fourth endodermal pouches. The fourth pouch was located in front of the nodosa ganglion. The bilateral fifth pharyngeal pouches protruded anterolaterally to form a Ushaped lumen surrounding the arytenoid swelling. During the middle stages, the third pharyngeal pouch was identified near the fourth pharyngeal artery and the fourth pharyngeal pouch was located anterior to the parathyroid gland IV. We identified a cyst-like structure that is composed of a cell cluster facing to a small lumen as the ultimobranchial body. During the late stages, the lateral thyroid arising from the fourth pharyngeal pouch was located medial to the common carotid artery and joined to dorsal surface of the thyroid gland anlage. The thymus anlage arising from the third pharyngeal pouch was an independent structure that was located lateral to the common carotid artery. However, the ultimobranchial body had disappeared and did not integrate in the thyroid gland. We concluded that (1) the thymus originates from the third pharyngeal pouch; (2) the lateral thyroid originates from the fourth pharyngeal pouch; (3) the ultimobranchial body originates from the fifth pharyngeal pouch

RESUMEN

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