What is the primary function of the respiratory system?

The primary function of the respiratory system is to facilitate gas exchange, which involves the uptake of oxygen from the environment and the release of carbon dioxide from the body. This process occurs in the alveoli of the lungs, where oxygen diffuses into the bloodstream while carbon dioxide diffuses out to be expelled from the body. This gas exchange is critical for maintaining cellular respiration, which provides the energy needed for various body functions.

While other systems and processes in the body are responsible for regulating blood pressure, transporting hormones, and absorbing nutrients, these functions are not associated with the respiratory system. Instead, they are key roles of the circulatory system, endocrine system, and digestive system respectively. Thus, the correct answer highlights the core role of the respiratory system in sustaining life through effective gas exchange.