Which of the following is a primary function of the respiratory system?

The primary function of the respiratory system is gas exchange, which involves the process of taking in oxygen from the atmosphere and expelling carbon dioxide from the body. This process occurs in the lungs, specifically in the alveoli, where oxygen diffuses into the bloodstream while carbon dioxide diffuses out to be exhaled.

Gas exchange is essential for sustaining cellular respiration, a biochemical process that cells use to produce energy. Without this effective gas exchange, the body's cells would not receive the oxygen needed for metabolism, leading to a deficiency in energy production and ultimately affecting overall health.

Other options listed are functions of different systems within the body. For instance, the absorption of nutrients is primarily a role of the digestive system, not the respiratory system. Regulation of blood sugar is managed by the endocrine system, particularly through hormones produced by the pancreas. Lastly, the production of hormones is also a function associated with various endocrine glands rather than the respiratory system. Therefore, the focus on gas exchange highlights its crucial role in maintaining the body's physiological balance and energy needs.