Epinephrine

Epinephrine is also known as adrenaline. It is a steroid hormone which is released by chromaffin cells in the adrenal glands as part of the 'fight or flight' response. This response can be induced by stress or other stimuli in the environment and causes many physiological effects such as increased heart rate; increased blood sugar levels (due to the conversion of glycogen to glucose in the liver); increased breathing rate; constriction of peripheral blood vessels and dilation of the pupils.

References

Alberts et al. (2008:G2), Molecular Biology of the Cell, 5th edition, New York: Garland Science