Final answer:
The kidneys regulate blood pH through tubular secretion. If blood pH is low, the kidney secretes hydrogen ions and reabsorbs bicarbonate ions. If blood pH is high, the kidney secretes bicarbonate ions and reabsorbs hydrogen ions.
Step-by-step explanation:
The third step of urine formation is tubular secretion, which occurs in the renal tubules. The kidneys play an important role in regulating blood pH through tubular secretion. If your blood pH is low (acidic), the kidney will respond by secreting hydrogen ions into the filtrate, which can be removed in the urine. To compensate, the kidney will reabsorb bicarbonate ions from the filtrate and return them to the blood.
On the other hand, if your blood pH is high (alkaline), the kidney will respond by secreting bicarbonate ions into the filtrate. This helps in removing excess bicarbonate ions from the blood, which can lower the blood pH. Additionally, hydrogen ions are reabsorbed from the filtrate and returned to the blood to further decrease its pH if needed.