"As you become angry your body's muscles tense up. Inside your brain, neurotransmitter chemicals known as catecholamines are released causing you to experience a burst of energy lasting up to several minutes. This burst of energy is behind the common angry desire to take immediate protective action. At the same time your heart rate accelerates, your blood pressure rises, and your rate of breathing increases. Your face may flush as increased blood flow enters your limbs and extremities in preparation for physical action. Your attention narrows and becomes locked onto the target of your anger. Soon you can pay attention to nothing else. In quick succession, additional brain neurotransmitters and hormones (among them adrenaline and noradrenaline) are released which trigger a lasting state of arousal. You're now ready to fight."

From: http://mentalhelp.net/poc/view_doc.php?type=doc&id=5805&cn=116