The structure in the human body primarily responsible for respiration is the lungs. The lungs are vital organs that facilitate gas exchange, allowing oxygen to enter the bloodstream and carbon dioxide to be expelled from the body. This process occurs in tiny air sacs within the lungs called alveoli, where oxygen passes into the blood while carbon dioxide is released for exhalation. The respiratory system, which includes the lungs, trachea, bronchial tubes, and diaphragm, works continuously to ensure that the body receives sufficient oxygen for cellular functions and removes waste gases.