This figure is a flow diagram summarising the regulation of body temperature in endotherms, using negative feedback. A change in blood temperature (too hot or too cold) is detected by specialised nerve cells, which relay a signal to the brain (the control centre). The brain responds to a 'too hot' message by sending neural signals to the skin which initiate dilation of blood vessels and sweating, which causes heat to be lost from the body. This results in a lowering of blood temperature which shuts off the 'too hot' signals to the brain. The brain responds to a 'too cold' message by sending out neural signals that cause constriction of blood vessels near the skin, initiate shivering in the muscles and increase metabolic rate. Together these responses cause release of heat within the body. This results in a rise of blood temperature which shuts off of the 'too cold' signals to the brain.