Endocrine glands

Endocrine glands are glands of the endocrine system that secrete their products, hormones , directlyinto the blood rather than through a duct. The main endocrine glands include the pituitary gland , pancreas , ovaries , testes , thyroid gland , and adrenal glands . The hypothalamus is a neuroendocrine organ. Other organs which are not so well known for their endocrine activityinclude the stomach , which produces such hormones as ghrelin .
Local chemical messengers, not generally considered part of the endocrine system, include autocrines , which act on the cells that secrete them, and paracrines , which act on a different cell typenearby.
The ability of a target cell to respond to a hormone depends on the presence of receptors, within the cell or on its plasma membrane, to which the hormonecan bind.
Hormone receptors are dynamic structures. Changes in number and sensitivity of hormone receptors may occur in response to high or low levels of stimulating hormones.
Blood levels of hormones reflect a balance between secretion and degradation/ excretion . The liver and kidneys are the major organs that degrade hormones; breakdown products are excretedin urine and feces.
Hormone half-life and duration of activity are limited and vary from hormone to hormone.