Final answer:
Decreasing the diameter of blood vessels to conserve heat is known as vasoconstriction. It involves the contraction of blood vessels in the skin to prevent excessive heat loss, contrasting with vasodilation, which increases blood flow and heat dispersal.
Step-by-step explanation:
Decreasing the diameter of blood vessels to conserve heat is referred to as vasoconstriction.
This physiological process occurs when blood vessels in the skin contract to prevent blood from flowing close to the surface of the body, which in turn reduces heat loss from the surface.
Conversely, vasodilation is the widening of blood vessels, which increases blood flow to the surface and helps to release heat when the body needs to cool down.
Vasoconstriction can be critical in cold environments; for example, when penguins stand on ice, they constrict the arterioles to their feet, dramatically decreasing blood flow and conserving heat for vital organs.
In humans, a similar response occurs when superficial arteries are constricted to minimize heat loss in response to cold temperatures.