Protein tubular breakdown

Regan et al. Tubular Breakdown of ET in Proteins where/fc is the bond decay given by... 

A 11 volume of urine from a healthy person contains approximately 1800 mg of urea, 200 mg of creatinine, 130 mEq of Na , 130 mEq of Cl , and lesser amounts of other ions. The concentrations of urea and creatinine, both of which are breakdown products of protein metabolism, are increased in the tubular fluid during flow through the tubule, due to a decrease in water flow rate. 

Most doctors use the plasma concentrations of creatinine, urea and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease. Protein and amino acid catabolism results in the production of ammonia, which in turn is converted via the urea cycle into urea, which is then excreted via the kidneys. Creatinine is a breakdown product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is mainly filtered by the kidney, though a small amount is actively secreted. There is little to no tubular reabsorption of creatinine. If the filtering of the kidney is deficient, blood levels rise. 

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