THE ENDOCRINE SYSTEM
Early gnathostomes evolved modifications of their
endocrine system which are shared with their terrestrial descendants.
In gnathostomes, a number of changes affected the endocrine system. The
GnRH gene was duplicated (Lovejoy, 1992) and POMC gene was translated
to produce multiple signaling molecules (Alrubaian, 2003). A portal system
developed between the hypothalamus and pituitary and the pars nervosa
became defined (Hoar, Vol. 2, p. 186-7). Growth hormone's function was
amplified to include both growth and diabetogenic effects (Hoar, Vol.
2). Gnathostomes evolved an ultimobranchial body (Hoar, Vol. 2;Shinohara-Ohtani,
1998), endocrine pancreatic islets located in compact exocrine tissue
(Hoar, Vol. 2; Youson, 1999), adrenal glands composed of adrenocortico
tissue (Hoar, Vol. 2), and androgen receptors (Thornton, 2001).