Health Science I – Anatomy, Physiology, and Medical Conditions Practice Test

When fear triggers a quick response, the body relies on the fight-or-flight system, which releases adrenaline from the adrenal medulla. Adrenaline acts rapidly to ready the body for action: it speeds up the heart to push more blood to muscles, opens the airways to improve oxygen intake, and mobilizes energy stores by triggering glycogen breakdown in the liver and muscles (and releasing fatty acids from fat tissue). This quick surge of glucose and oxygen provides the fuel and readiness needed for fast running. Other hormones don’t produce this immediate, all-systems-up readiness—insulin lowers blood sugar and promotes storage, thyroxine changes metabolism more slowly, and estrogen isn’t involved in an acute sprint response.