Three basic pathophysiologic mechanisms lead to virtually all the clinical disease states involving endocrine glands: {{U}}(46) {{/U}} the excessive hormone production and action and neoplasa. Deficiency of hormone action is most commonly caused by an abnormally low level of biologically active hormone reaching target tissues. {{U}}(47) {{/U}} Endocrine gland hypofunciton may be congenital, caused by a complete failure of gland development, a mutant gene-encoding the structure of hormone or an enzyme responsible for hormone biosythesis. {{U}} (48) {{/U}} replacement by tumor, surgical extirpation, effects of pharmacologic or environmental agents, or inflammation. Other causes of decreased hormone action in target tissues are encountered less frequently. Deranged physiologic control of pituitary gland function causes secondary glandular failure, which can be either congenital or acquired {{U}}(49) {{/U}} Defective postsecretory hormone activation or accelerated hormone metabolism may result in abnormally low hormone activity. Hormonal deficiency states, despite normal or even elevated concentrations of biologically active hormone in the circulation, may be due to target-tissue resistance. {{U}} (50) {{/U}} This failure of target tissue responsiveness may be due to an abnormality of hormone receptors or in post-binding signaling of the hormone-receptor interaction.

E. Resistance can be congenital or acquired F. Endocrine gland failure may also be acquired as a consequence of physiologic atrophy.