Homeostasis

Water is taken into the body through food and drink.

It leaves the body in the following ways:

• 1) Through skin as SWEAT
• 2) Via the lungs as BREATH
• 3) Via the kidneys as URINE

HOT DAY or EXERCISING

• Sweat a lot
• Produce less urine to conseve water but it is concentrated so darker in colour
• Lose more water through your breath when exercising

COLD DAY or NOT EXERCISING

• Don't sweat as much
• Produce more urine, which will be pale because the waste in the urine has become more diluted

WHEN YOU'RE TOO HOT

• Lots of sweat is produced - when it evapourates, it transfers heat from your skin to the environment, cooling you down
• VASODILATION - blood vessels close to the surface of the skin widen. This allows more blood to flow to the surface so it can radiate heat out into the surroundings.
• Hairs lie flat

WHEN YOU'RE TOO COLD

• Very little sweat is produced
• VASOCONSTRICTION - blood vessels close to the surface of the skin constrict so less heat can be transferred from the blood to the surroundings
• Hairs stand on end to trap an insulating layer of air to keep you warm
• You shiver and the movement generates heat in your muscles. Exercise does the same.