Adrenaline speeds up your breathing and heart rate to prepare you to run from danger. It causes your pupils to grow bigger to allow you to take in as much visual information as possible. It slows down your digestive process so that the energy can be redirected to your muscles.
Adrenaline also causes your blood vessels to dilate (called vasodilation), in order to improve blood-flow and oxygen delivery. This is the case with blushing.
The veins in your face respond to a signal from the chemical transmitter adenylyl cyclase, which tells the veins to allow the adrenaline to do its magic. As a result, the veins in your face dilate, allowing more blood to flow through them than usual, creating the reddened appearance that tells others you're embarrassed. In other words, adrenaline causes more local blood flow in your cheeks.
I love the 'blush' - that comes from the sun; after you've put on your sun-blocker, head out and enjoy it...Vitamin D can't work well without it! Stay bronzed and stay healthy!
Robin Urton's art: http://eyeconart.net.
Get recipes for good health: http://cookinglight.com.