Body and drug basics
Absorption
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Absorption is the step where a substance crosses from wherever it was put into the bloodstream: through the wall of the gut, through skin, or out of the tissue under the skin. It is a barrier-crossing problem, and molecules that are large or strongly water-loving cross poorly, which describes most peptides. Absorption can be slow and complete, fast and partial, or very nearly nil.
Why it matters here
How fast something is absorbed sets how sharply levels peak, which is a separate question from how much arrives in total. It is also only the first of several steps, so being absorbed is not the same as being available to the body.
What it is not
Absorption is not bioavailability, and the two words are used as though they were the same thing constantly. Absorption is just the crossing; bioavailability is what survives everything between the point of entry and general circulation, including being broken apart on the way.
Also called
- absorption
- absorbed
- absorb
- uptake
- rate of absorption
- absorption rate
Often called uptake, particularly when describing entry into a specific tissue rather than into the blood generally.
Compounds carrying this term
None on file yet. This term is in the controlled vocabulary but no compound record currently uses it — which is a statement about our coverage, not about the term.