When adrenaline is secreted into the bloodstream, the body undergoes a rapid and coordinated "fight-or-flight" response to prepare for immediate physical action. Key physiological changes include:

• Increased heart rate and stronger heart contractions , which pump more blood to muscles and the brain, supplying oxygen and energy needed for quick responses

• Dilation of air passages in the lungs , allowing faster and deeper breathing to increase oxygen intake

• Redistribution of blood flow , with blood vessels constricting in the skin and digestive system to reduce blood flow there, while increasing blood flow to major muscles and the brain for enhanced performance

• Increased blood sugar levels by stimulating the liver to convert glycogen into glucose, providing a quick energy source for muscles and brain cells

• Pupil dilation , which improves vision and alertness

• Increased sweating , which helps regulate body temperature during heightened activity

• Reduced sensitivity to pain , allowing continued functioning even if injured

• Slowed digestion , as blood flow is diverted away from the gut to prioritize muscles and brain

• Suppression of insulin production , which helps keep blood glucose levels elevated for energy use

These changes collectively enhance physical performance, alertness, and energy availability, enabling the body to respond effectively to stress or danger. The response is initiated by the brain's amygdala detecting threat, signaling the hypothalamus, which activates the sympathetic nervous system and stimulates the adrenal medulla to release adrenaline into the blood

. In summary, adrenaline secretion triggers a comprehensive physiological shift to maximize oxygen and energy delivery to muscles and brain, preparing the body for rapid and vigorous action in stressful situations