Endocrine gland

Definition

A ductless gland that synthesizes and secretes hormones directly into the hemolymph or bloodstream, rather than through a duct to an external or internal surface. In arthropods, endocrine glands are critical regulators of development, reproduction, and metabolism, with hormones often acting on distant target tissues to coordinate physiological processes.

Etymology

From Greek endon (within) + krinein (to separate or secrete), referring to internal secretion directly into circulation

Example

In insects, the corpora allata are paired endocrine glands located behind the brain that secrete juvenile hormone, which maintains larval characteristics and suppresses metamorphosis; removal of these glands triggers premature pupation in holometabolous species.

Synonyms

• ductless gland

Related Terms

• Exocrine gland
• neurosecretory cell
• corpus allatum
• corpus cardiacum
• prothoracic gland
• Ecdysone
• Juvenile hormone
• Hormone
• Hemolymph

Usage Notes

Contrast with exocrine glands, which release products through ducts to external surfaces or body cavities. In arthropods, the distinction can be subtle: some neurohemal organs (e.g., corpora cardiaca) store and release hormones synthesized elsewhere, blurring the line between pure endocrine function and neurosecretory activity. The term is sometimes used more broadly to include neuroendocrine structures, though purists reserve it for non-neural secretory tissue.