Here's why:

* Kidneys' role in acid-base balance: The kidneys are the primary regulators of blood pH. They do this by:

* Filtering waste products: The kidneys remove excess acids and bases from the blood, preventing their accumulation.

* Adjusting bicarbonate levels: Bicarbonate is a crucial buffer in the blood, and the kidneys can adjust its reabsorption and excretion to maintain the proper pH balance.

* Producing ammonia: Ammonia helps neutralize excess acids in the urine.

* Urine's pH range: The pH of urine can fluctuate significantly depending on the body's acid-base status. It can range from around 4.5 (acidic) to 8 (alkaline).

While other systems like the respiratory system (lungs) also play a role in regulating pH, the urinary system has the greatest capacity for long-term adjustments to blood pH. The lungs primarily regulate pH through CO2 levels, which is a faster process, but the kidneys provide a more sustained and fine-tuned control over acid-base balance.