CREATININE
Creatinine ash is a basic byproduct in the breakdown of muscle creatine phosphate resulting from energy metabolism.
From a pathological perspective the kidneys primarily remove creatinine and when there are elevated levels it indicates reduced kidney function. Thus creatine levels give an approximate for the GFR.
From a physiological perspective, creatine is a by-product of actin metabolism after being exposed to acetylcholine combustion.
The actin fiber joins two stable protein blocks (myosin), which combusts to produce muscle contraction, primarily for activity and secondarily for tonicity.
During a muscle contraction, an action potential travels along a motor nerve to a muscle fiber. Acetylcholine is released at the motor endplate, causing multiple acetylcholine lined gated protein channels to open.
This causes sodium ions to flow to the interior of the muscle, which initiates an action potential of that muscle.
This then leads to depolarization releasing large amounts of calcium into the myofibrils. This initiates a contractive force between the actin and myosin filaments via ATP causing them to slide together, which is the contractile process. After a fraction of a second, calcium is pumped back into the sarcoplasmic reticulum, until the next muscle contraction.
The actin fiber is then oxidized (H displaced) via acetylcholine, leaving an oily waxy residue known as creatinine. GABA (Glutamic amino benzoic acid), which is part of the actin fiber, helps it burn better.
Creatine becomes creatinine with the release of ATP.
Low creatinine levels would indicate muscle loss and weakness.