The anterior pituitary (adenohypophysis, or pars distalis) is derived from an upward evagination of pharyngeal epithelium known as Rathke's pouch. The pituitary develops embryologically from two sources. Thus, endocrine glands are highly vascularized with many small capillaries among the nests of endocrine cells. Endocrine glands secrete directly into the bloodstream, not through a duct system. Thus, the hormones secreted by the endocrine glands enter the circulation and are carried throughout the body to act upon target cells located far away from the secreting glands. Įndocrine: the substance acts upon other cells at a distance.Paracrine: the substance acts upon other cells in the immediate vicinity-a localized effect Substances secreted by cells can have several actions:Īutocrine: the substance acts upon the cell that secreted it-an autofeedback mechanism Endocrine Organs Endocrine Organs Return to the Histology Tutorial menu.
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