Final answer:
Large amounts of epinephrine and norepinephrine, known as 'fight or flight' hormones, are released into the bloodstream in response to stress and fear, triggering physiological changes to prepare the body to confront or escape threats.
Step-by-step explanation:
Stress and fear release large amounts of epinephrine and norepinephrine into the blood system. These hormones are often referred to as "fight or flight" hormones because they prepare the body to either confront or escape from a threat. When the sympathetic nervous system is activated during stressful situations, it releases adrenaline to accelerate heart rate and respiration. Epinephrine dilates blood vessels and increases heart and respiratory rates, while norepinephrine constricts the smooth muscles of blood vessels, affecting the flow of blood into the kidneys' nephrons.
Additionally, the HPA axis is activated, and cortisol is secreted by the adrenal glands, which can influence every organ in the body and is known as a stress hormone. It’s important to note that while the fight-or-flight response was essential for survival in the face of physical threats faced by our ancestors, in modern times, chronic psychological stress can lead to negative health consequences like heart disease and weakened immune systems.