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Why does warm blood flow to the skin when the body needs to lose heat?
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blood
Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).
When the body needs to lose heat, it directs warm blood to the skin to facilitate the transfer of thermal energy to the external environment. This process is managed by the hypothalamus, which acts as the body's thermostat.12
When the hypothalamus detects a rise in blood temperature, it sends nerve impulses to control the diameter of blood vessels in the skin. Specifically, it triggers vasodilation—the widening of these vessels—which increases blood flow to the surface of the body. As this warm blood reaches the skin, the heat is dissipated into the surroundings. This physiological mechanism is a critical component of thermoregulation, often working in tandem with sweating to maintain a stable core body temperature.132