What is one of the primary functions of the kidneys?

The primary function of the kidneys is to filter blood waste and excess water. This filtration process occurs in the nephrons, the functional units of the kidneys, where blood is processed to remove waste products such as urea, creatinine, and various toxins. In addition to filtering waste, the kidneys regulate the volume and composition of body fluids by excreting excess water and electrolytes, thus maintaining homeostasis.

This function is critical for the body's overall health, as ineffective waste removal can lead to conditions such as uremia, where harmful substances build up in the blood due to kidney dysfunction. The kidneys also play an essential role in regulating blood pressure through the renin-angiotensin-aldosterone system and in maintaining the balance of important minerals like potassium and sodium.

The other options refer to different physiological processes. Hormones related to digestion are primarily produced in the pancreas and other parts of the digestive system. Blood sugar regulation is mainly controlled by the pancreas through insulin and glucagon. Heart rate control is influenced by the autonomic nervous system and various hormones, not directly by kidney function. Thus, filtering blood waste and excess water is indeed the correct and primary function of the kidneys.