Which of the following is NOT part of the gastrointestinal system?

The kidneys are not part of the gastrointestinal system; they are part of the urinary system, which is responsible for filtering waste products from the blood and excreting them as urine. The gastrointestinal system, on the other hand, includes organs that are directly involved in the digestion and processing of food.

The esophagus, liver, and pancreas all play essential roles in this system. The esophagus transports food from the mouth to the stomach, the liver produces bile and processes nutrients, and the pancreas contributes digestive enzymes that help break down food in the small intestine. Therefore, identifying the kidneys as the option that does not belong to the gastrointestinal system is accurate and reflects an understanding of the anatomical and functional distinctions between these organ systems.