Which organ is primarily responsible for filtering and excreting waste from the blood?

The kidneys are primarily responsible for filtering and excreting waste from the blood. They perform this essential function by removing excess waste products and fluids from the bloodstream, which are then excreted as urine. The kidneys contain millions of tiny structures called nephrons, which filter the blood, reabsorb necessary substances, and excrete waste materials, contributing to the regulation of electrolyte balance and blood pressure.

The liver is involved in processing nutrients and detoxifying harmful substances but does not filter blood in the same manner as the kidneys. The pancreas primarily functions as an endocrine gland that regulates blood sugar levels and as an exocrine gland that produces digestive enzymes. The spleen plays a role in immune response and the filtering of blood cells, but its function does not center around the excretion of waste from the blood. Thus, the kidneys are the organs most critical in maintaining homeostasis by filtering and excreting waste in the urinary system.