Which structures are part of the respiratory system?

• A. Kidney, Bladder
• B. Heart, Arteries
• C. Liver, Gallbladder
• D. Nose, nose hair, mouth, pharynx, larynx, trachea, lungs, bronchi, bronchioles, alveoli, diaphragm

Answer: (D)

Breathing relies on a coordinated set of airways and lung tissues that bring in oxygen and remove carbon dioxide. The nose and its hairs help filter air as it enters. The mouth can also admit air, and the pharynx and larynx guide air downward toward the lungs. The trachea splits into the main bronchi, which branch into bronchioles and end in tiny air sacs called alveoli where gas exchange occurs. The diaphragm is the primary muscle that drives breathing by expanding and contracting the chest cavity, letting air flow in and out.

The other systems don’t belong to the respiratory system. The kidneys and bladder handle waste in urine, the heart and arteries pump and move blood, and the liver and gallbladder aid digestion and bile production. These structures are part of the urinary, circulatory, and digestive systems, not the respiratory system.