We sweat so our bodies stay cool. Sweating uses a special process called cellular respiration. It absorbs glucose and oxygen to produce ATP, the primary energy source of a cell. Most of this process is done in a structure called the mitochondria. The more you move, the harder it is for this structure to make energy for the body.
All this has a price, though. When cells break down the ATP, they let go of heat. The warmth stimulates temperature sensors all over your body. Those parts look for the excess heat made by muscle cells. Then they send a signal to your hypothalamus, which is your body’s internal thermostat. It regulates your body temperature, and it responds by sending a signal to your sympathetic nervous system to the sweat glands in your skin, which are scattered throughout your body.
The sweat glands first receive signals from your skin, and the solution around the cell is filled with lots of sodium and chloride. Then, the cells pump charged particles into a hollow tube that goes through the sweat gland. Since it is salty on the inside of the tube, water is moved into the tube by osmosis. As something called the primary secretion builds up in the base of the tube, water pressure shoves itself up into the long, straight part of the duct. Before the sweat leaks onto your skin, the cells surrounding the tube will recover as much salt as they can, so the process can go on.
The liquid in your sweat absorbs your body’s heat energy and evaporates, cooling your body down. This process is called evaporative cooling.
This cooling effect isn’t just helpful during exercise; we sweat in many more situations. Some people sweat when eating spicy food because it triggers their brain, which signals the same parts that look for extra heat, and then the same process from the beginning. Some people sweat when they are nervous. This is because adrenaline stimulates muscle activity, which causes blood vessels to expand. Some people sweat when they are sick. When they have a fever, they sweat because infections stimulate the hypothalamus to increase muscle activity.
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