What is filtered and both actively reabsorbed and actively secreted?

The substance that is both filtered and actively reabsorbed and secreted is typically a type of ion or solute, such as potassium (K+) in the kidneys. During renal function, potassium is filtered out of the blood in the glomerulus, then actively reabsorbed in the proximal tubule and loop of Henle, and finally actively secreted in the distal tubule and collecting duct. This dual process helps regulate potassium levels in the body, maintaining homeostasis.