Medical Definition of internal
1: existing or situated within the limits or surface of something: asa: situated near the inside of the body <an internal layer of abdominal muscle>b: situated on the side toward the midsagittal plane of the body <the internal surface of the lung>
2: present or arising within an organism or one of its parts <an internal stimulus>
3: applied or intended for application through the stomach by being swallowed <an internal remedy>
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