Physiological changes refer to the alterations in the body's functions and processes that occur in response to various factors, such as age, environment, or health conditions. These changes can affect systems like the cardiovascular, respiratory, and digestive systems, leading to variations in heart rate, breathing patterns, and nutrient absorption. For example, during exercise, the body experiences increased heart rate and blood flow to supply muscles with more oxygen. Similarly, as people age, they may experience changes in metabolism and hormone levels, which can impact overall health and energy levels.