Which organ is NOT part of the digestive tract?

The kidney is not part of the digestive tract because its primary function is related to the excretory system rather than the digestive process. The digestive tract includes organs that are directly involved in the process of digestion and the movement of food from entry to exit in the body. This includes the mouth, esophagus, stomach, small intestine, and large intestine, which all play roles in breaking down food, absorbing nutrients, and expelling waste. The kidneys, on the other hand, are responsible for filtering blood, regulating fluid and electrolyte balance, and producing urine to excrete waste products from metabolism. Therefore, while involved in maintaining overall homeostasis, the kidneys do not participate in the digestion of food, distinguishing them from the other options listed.