Physiological reactions are the body's automatic responses to various stimuli, such as stress, danger, or changes in the environment. These reactions involve the nervous system and endocrine system, which work together to regulate bodily functions. For example, when faced with a threat, the body may enter a fight-or-flight response, increasing heart rate and releasing hormones like adrenaline. These reactions can also occur in response to everyday situations, such as eating or exercising. When you eat, your body releases insulin to help manage blood sugar levels. Similarly, during physical activity, your muscles require more oxygen, prompting an increase in breathing and heart rate to meet the demand.