If a body temperature is too high some blood vessels increase in size and sweat glands will excrete sweat resulting in a lower body temperature these changes an example of

Explanation:

When the body temperature rises, such as when exercising on a hot day, the dermal blood vessels dilate, and the sweat glands begin to secrete more sweat. ... This can include an inhibition to excessive sweating and a decrease of blood flow to the papillary layers of the skin.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

carbon atoms, hydrogen, oxygen, and nitrogen.