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

The liver is primarily involved in metabolic processes, including detoxification, protein synthesis, and the production of biochemicals necessary for digestion. While it plays a role in the overall processing of waste products in the body, it is not classified as part of the excretory system, which specifically focuses on the organs responsible for the elimination of waste from the body. The excretory system comprises the kidneys, ureters, bladder, and urethra, which work together to filter blood, remove waste, and excrete urine. This distinction clarifies the liver's function compared to the other options, which are directly involved in waste removal.