Describe how an endotherm prevents its body temperature from rising when external temperatures increase?

An endotherm detects external temprature increases through peripheral skin receptors just beneath the skins surface. This causes impulses (action potentials) to travel to the thermoregulatory centre in the Hypothalumus (located in the brain). This stimulates a range of physiological and behvaioural responses designed to lower the core temprature of the endotherm. The vasodilation of arterioles and capillaries occurs to maximise heat loss through the skin via radiation, conduction and convection. Shunt vessels below the capillaries constrict to push blood closer to the skin's surface and into the capillaries. Respiration may well decrease in the liver, causing less heat to be generated by the body. Sweat glands become active, releasing water onto the skins surface which then evaporates using body heat (and hence transfers heat away from the body). Endotherms may then change their behaviour to maximise heat loss, perhaps by moving into shade, stretching out (to increase SA:V, and increase heat exchange) or by immersing themsleves in cool water.