What are the primary functions of the kidneys?

The primary functions of the kidneys center around maintaining homeostasis within the body, primarily through the regulation of fluid balance and the filtration of waste products from the bloodstream. The kidneys play a crucial role in controlling the volume and composition of body fluids, which includes balancing electrolytes such as sodium and potassium, as well as maintaining acid-base balance.

Additionally, the kidneys are responsible for filtering blood to remove metabolic waste products, such as urea and creatinine, which are then excreted in urine. This filtration process is essential for preventing the accumulation of toxins in the body and for ensuring that the body's internal environment remains stable.

In contrast, the other options presented relate to different organ systems and their respective functions. For instance, the production of insulin and regulation of blood glucose is primarily the function of the pancreas. Digesting fats and absorbing nutrients takes place in the digestive system, particularly in the small intestine. Lastly, storing bile for digestion is a function of the gallbladder, which aids in the emulsification of fats during the digestive process.