BIOCHEMISTRY - Main Regulators and Biological Fluids of the Human Body - 2016

4. CHEMICAL COMPOSITION OF URINE

4.5. Chemical composition of urine

Every 24 hours, 50 - 75 g of dissolved substances are excreted in the urine. About 150 different compounds have been identified in urine.

4.5.1. Inorganic constituents of urine

Practically all inorganic Blood components are constantly present in urine. The total daily excretion of inorganic substances ranges from 15 to 25 g. The most abundant

inorganic compound in urine is sodium chloride (8 - 15 g/day). Additionally, potassium, calcium, magnesium, and ammonium cations, as well as phosphate, bicarbonate, and sulfate anions, are always present in urine.

4.5.2. Organic constituents of urine

Urea. Quantitatively, urea is the most abundant nitrogenous waste product excreted in urine (20 - 35 g/day).

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Urea is the end product of Protein Catabolism; its urinary concentration serves as an indicator of the Rate of protein breakdown in the body.

Uric acid. This nitrogenous compound, constantly present in urine (0.7 g/day), is the end product of nucleic acid catabolism. Uric acid has low solubility in Water and may therefore precipitate out in collected urine samples.

Creatinine. This is the end product of creatine phosphate breakdown, stores of which are concentrated in Muscle tissue. Consequently, There is a clear correlation between urinary creatinine levels (typically 1 - 2 g/day) and muscle mass development.

Certain Enzymes, Vitamins, and Hormones may also be detected in urine.

4.5.3. Pathological components of urine

Pathological components appear in urine in various diseases and following high-volume physical exertion.

Protein. The presence of protein in urine in large quantities is termed proteinuria. The primary cause of proteinuria is an increase in the permeability of the renal filtration barrier. Proteinuria is frequently observed in Kidney diseases, Heart Failure, and under heavy physical stress.

Glucose. Elevated urinary glucose levels (glucosuria) occur in certain conditions, such as Diabetes Mellitus (hyperglycemic glucosuria) and renal disease (renal glucosuria), as well as following intense training and competitive loads.

Ketone Bodies. The excretion of large amounts of ketone bodies in the urine (ketonuria) occurs when the body aggressively breaks down fat reserves instead of CARBOHYDRATES to generate energy (e.g., in diabetes mellitus, fasting, or prolonged Physical Exercise). Ketone bodies (acetoacetic acid, 3-hydroxybutyric acid) are intermediate metabolites of lipid catabolism. In such cases, acetone—formed in the blood from excess acetoacetic acid—is also detected in the urine.

Blood. During inflammatory processes or traumatic injuries within the Urinary System, red Blood Cells (erythrocytes) appear in the urine (Hematuria). In athletes, hematuria is typically traumatic in nature.