ENDOGENOUS

adj. originating from within

The word endogenous means "arising from within", the opposite of exogenous.
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Adjective
1. of or resembling an endogen
(pertainym) monocot, monocotyledon, liliopsid, endogen
2. derived or originating internally
(synonym) endogenic
(antonym) exogenous, exogenic

(a.)
Originating from within; increasing by internal growth.
  

(a.)
Increasing by internal growth and elongation at the summit, instead of externally, and having no distinction of pith, wood, and bark, as the rattan, the palm, the cornstalk.
  

Inside. For example, endogenous cholesterol is cholesterol that is made inside the body and is not in the diet.