thyroid gland

[Guest Hippokrates]

due to its development the thyroid gland is a exocrine gland, that was "converted" into a endocrine one producing the hormones T3 (Trijodthyronine) & T4 (Thyroxine)

* Primarily it's connected to the oral cavity via the thyroglossal duct, which then regresses.

* it is also is the only "endocrine" gland, that stores its product extracellularly (in the follicles).

* these follicles can be seen as "acini" (like in pancreas), that have lost their excetory duct. (see above)

 

does anyone know an animal in which the homologous structure to our thyroid gland still serves that exocrine purpose?

afaik this hypothetical creature must be very far related to us humans, because even in in the amphibians there is thyroxine. there it serves as an metamorphosis-inducing factor. (But i have to admit that i dont know if this amphibian T4 is produced in an amphibian thyroidea.)

 

thx hippokrates