Which of the following organs is NOT included in the respiratory system?

The heart is not part of the respiratory system. The primary function of the respiratory system is to facilitate gas exchange, providing oxygen to the body and removing carbon dioxide, which involves specific organs and structures designed for this purpose.

The lungs are the key organs in the respiratory system where gas exchange occurs. They are equipped with alveoli, small air sacs where oxygen and carbon dioxide are exchanged between the air and the blood. Airways, which include the trachea and bronchial tubes, serve as passages for air to enter and exit the lungs. In addition, respiratory muscles, primarily the diaphragm and intercostal muscles, aid in the mechanics of breathing by expanding and contracting the thoracic cavity.

Thus, while the heart plays an essential role in the circulatory system by pumping blood and transporting oxygen to various tissues, it is not structurally or functionally involved in the respiratory processes. Therefore, identifying the heart as not being part of the respiratory system highlights the distinction between these two critical systems in the body.