Exogenous

Definition

Originating from outside an organism, tissue, or defined biological system; produced or introduced by external factors rather than generated internally. In physiology and ecology, contrasts with endogenous processes or substances that arise from within the system itself.

Etymology

From Greek exō- 'outside' + -genēs 'born, produced'

Example

Exogenous heat gain in basking butterflies comes from solar radiation absorbed through the wings and body, supplementing the limited endogenous heat produced by thoracic muscle activity.

Synonyms

• external
• ectogenic

Related Terms

• Endogenous
• ectothermy
• Exoskeleton
• allochthonous
• abiotic factor

Usage Notes

In arthropod physiology, exogenous is often paired with endogenous to distinguish environmental inputs (exogenous nutrients, temperature cues, photoperiod) from internally regulated processes (endogenous rhythms, metabolic heat, hormone titers). In disease ecology, 'exogenous infection' denotes pathogen acquisition from outside the host versus 'endogenous' reactivation of resident microbes. Not to be confused with exogeny in geology (external surface processes).