Which anatomical structure is NOT part of the respiratory system?

The liver is not part of the respiratory system, which primarily comprises the structures involved in the process of breathing and gas exchange. The respiratory system includes the trachea, bronchi, diaphragm, and lungs, all of which play essential roles in facilitating the intake of oxygen and the expulsion of carbon dioxide.

The trachea serves as the windpipe that connects the larynx to the bronchi and allows air to pass into the lungs. The bronchi are the large passageways that branch from the trachea into each lung, further distributing air for gas exchange. The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity; its contraction and relaxation control breathing by changing pressure in the thoracic cavity.

In contrast, the liver is a vital organ involved in various functions related to metabolism, detoxification, and bile production but does not play a role in respiration. Understanding the specific functions and structures associated with the respiratory system helps clarify why the liver is not included in this category.