Chemicals that prevent the pH of a solution from changing are called buffers. Blood buffers are NaHCO3, Na2HPO4, KHCO3 etc. Nephron tubular cells reabsorb ions such as Na+, K+, HC3-, PO43- etc. from the glomerular filtrate into the blood. These ions participate in the formation of buffers in the blood and prevent changes in blood pH.
Na+ + HCO3- → NaHCO3
2Na+ + HPO43- → Na2HPO4
K+ + HCO3- → KHCO3