Final answer:
The active and selective renal process in urine formation in which substances such as drug metabolites, urea, creatinine, etc., are added to the filtrate from blood or tubular cells is called tubular secretion.
Step-by-step explanation:
The active and selective renal process in urine formation in which substances such as drug metabolites, urea, creatinine, etc., are added to the filtrate from blood or tubular cells is called tubular secretion. Tubular secretion is an important mechanism in eliminating certain substances from the blood and adding them to the urine.
In tubular secretion, substances move from the blood vessels surrounding the nephron called the peritubular capillaries, into the renal tubules. This process occurs primarily in the proximal convoluted tubule (PCT), although some tubular secretion can also occur in the distal convoluted tubule (DCT) and collecting ducts.
Tubular secretion plays a vital role in the elimination of waste products, maintaining electrolyte balance, and regulating the pH of the urine. By removing certain substances from the blood and adding them to the urine, tubular secretion helps in the excretion of waste, maintaining homeostasis, and overall kidney function.