Adrenaline, secreted into the blood, accelerates the heart rate, increasing oxygen supply to muscles. It also causes the contraction of muscles around small arteries in the digestive system and skin, redirecting blood flow to skeletal muscles.

In various animals, including humans, adrenaline is secreted from the adrenal glands, serving as a hormonal signal that triggers wide-ranging changes in different tissues, preparing the body for activities such as fighting or fleeing in response to a threatening situation.

Hormones like adrenaline provide a wider range of tissue responses by reaching all cells in the body, allowing for coordinated and energy-efficient preparations for activities like fighting or fleeing, which would be limited with only electrical impulses via nerve cells.

Animals, such as squirrels, prepare for activities like fighting or running away through the release of the hormone adrenaline from the adrenal glands, facilitating widespread changes in various tissues to conserve energy and coordinate responses.

Auxin is synthesized at the shoot tip and, when light is detected, it diffuses towards the shady side of the shoot. Concentration of auxin on the shaded side stimulates cell growth, causing the plant to bend towards the light.