A diagram of six changes that occur when the body overheats. 1. Sweating leads to dehydration. When you sweat a lot, you lose water and need to drink to replace fluids leaving the body. 2. Blood volume decreases. Your heart has to work harder because of dehydration, which means less blood volume in your body. 3. Skin gets more blood. When body gets hot, more blood goes to the skin surface and you sweat to cool blood and body. 4. Kidneys respond. When body gets dehydrated, kidneys must work more to rid body of salt and to keep more water in body. Urine gets concentrated. 5. Breathing gets rapid. Breathing becomes fast and deep to increase oxygen level and decrease CO2 level. 6. Carbon dioxide builds up in the body's cells when the body temperature overheats. This leads to poor circulation.