When adrenaline is secreted into the blood, the body responds by initiating the "fight or flight" response, which prepares it to react quickly to stress or danger. Key physiological changes include:

• The heart beats faster, increasing the supply of oxygen-rich blood to muscles.
• Breathing rate increases as airways dilate, allowing more oxygen into the lungs.
• Blood flow is redirected from non-essential functions like digestion and skin to the skeletal muscles.
• The liver releases glucose into the bloodstream to provide immediate energy.
• Blood pressure rises due to constriction of certain blood vessels.
• Pupils dilate to improve vision.
• Mental alertness sharpens.
• The body's ability to feel pain decreases temporarily, and sweating increases to cool the body.

These changes collectively enhance physical strength, speed, and alertness to deal with threats or stressful situations effectively.