Titratable acid

Titratable Acid refers to the amount of base, usually expressed in milliequivalents, that is required to bring the pH of a solution to a predetermined value. In the context of renal physiology, it plays a crucial role in the body's mechanism for maintaining acid-base balance. The kidneys regulate blood pH by adjusting the excretion of hydrogen ions and bicarbonate in the urine, and titratable acidity is a key component of this process.

Physiology

The kidneys maintain acid-base homeostasis through three main mechanisms: reabsorption of bicarbonate, excretion of hydrogen ions, and production of new bicarbonate. Titratable acid excretion is part of the hydrogen ion excretion mechanism. The primary titratable acid in urine is phosphoric acid, although other organic acids can also contribute. The process involves the secretion of hydrogen ions into the renal tubule, where they bind to phosphate ions (HPO4^2−), forming weak acids (H2PO4−) that can be excreted in the urine.

Clinical Significance

Alterations in the excretion of titratable acid can indicate or contribute to various clinical conditions. For example, in metabolic acidosis, the body compensates by increasing the excretion of hydrogen ions as titratable acids and ammonium ions in the urine. Conversely, in conditions where renal function is impaired, such as chronic kidney disease, the ability to excrete titratable acids may be reduced, contributing to acidosis.

Measurement

The measurement of titratable acid involves collecting urine over a specified period, usually 24 hours, and then titrating the urine with a strong base, such as sodium hydroxide (NaOH), to a predetermined pH, often pH 7.40, which is the normal pH of blood. The amount of base required to reach this pH is a measure of the titratable acidity of the urine.

Related Pages

• Acid-base homeostasis
• Renal physiology
• Metabolic acidosis
• Chronic kidney disease

See Also

• Ammonium excretion
• Bicarbonate reabsorption