a. urinary excretion = tubular reabsorption + tubular secretion – Glomerular filtration.

Tubular reabsorption: Tubular reabsorption is the process by which the nephron removes water and solutes from the fluid from the tubules (pre-urine) and returns the same to the blood which is circulating.

Tubular secretion: It is secretion of H⁺ and NH₄⁺ from the blood into the tubular fluid that helps to keep blood pH and maintain osmolarity.

b. Dialysis fluid = Plasma– nitrogenous wastes

Nitrogenous wastes: Any metabolic waste product that contains nitrogen is called nitrogenous wastes.