Which organs are part of the renal system and are responsible for filtering blood?

The kidneys are vital components of the renal system, primarily responsible for filtering blood to remove waste products and excess substances, thus playing a crucial role in maintaining the body's homeostasis. They regulate electrolyte balance, blood pressure, and the volume of blood by selectively reabsorbing substances the body needs and excreting those that are unnecessary or harmful through urine formation.

In addition to filtration, the kidneys also produce hormones, such as erythropoietin, which stimulate red blood cell production, and they help in the regulation of pH levels in the body. Their structural units, called nephrons, are specifically designed for this filtration and reabsorption process.

Other organs listed, such as the liver, spleen, and pancreas, have different primary functions. The liver is mainly involved in metabolic processes and detoxification, the spleen plays a role in immune function and recycling of red blood cells, and the pancreas is crucial for digestion and regulation of blood sugar levels. Thus, these organs are not integral to the blood filtration process performed by the renal system.