The paired adrenal glands are small, yellow masses of tissue that lie in contact with the upper ends of the kidneys. Each gland consists of a central portion, the adrenal medulla and a larger outer section, the adrenal cortex. The adrenal medulla is a neuro-endocrine gland that is coupled to the sympathetic nervous system. It develops from neural tissue and its secretion is controlled by sympathetic nerves. The adrenal medulla secretes epinephrine and nor epinephrine. Chemically, these hormones are very similar; they are amino acid derivatives that belong to the chemical group known as catecholamines. Most of the hormone output of the adrenal medulla is epinephrine. During a stressful situation, adrenal medullary hormones initiate an alarm reaction that enables us to think more quickly, fight harder or run faster than usual. Metabolic rate increases by as much as 100%. Blood vessels going to the brain, muscles and heart are dilated, whereas those to the skin and kidneys are constricted. Constriction of blood vessels serving the skin has the added advantage of decreasing blood loss in case of hemorrhage (and explains the sudden paling that comes with fear or rage). At the same time, the heart beats faster. Strength of muscle contraction increases. Thresholds in the reticular activating system of the brain are lowered, so we become more alert. The adrenal medullary hormones also raise fatty acid and glucose levels in the blood (through glycogen breakdown), ensuring needed fuel for extra energy.