The name for ‘constancy of the internal environment’ is homeostasis. The body must regulate many body systems and processes to keep inner conditions stable. The temperature nucleus in the hypothalamus controls heat loss and production by the body through the skin. Overheating
(A) causes and increased blood flow from the blood vessels
(1), to radiate heat and causes sweating through the sweat glands
(2), to lose heat. A fall in body temperature
(B) constricts the surface blood vessels, stops sweating and makes the erector muscles
(3) contract, causing the hairs
(4) to stand on end, trapping air as an insulating layer. Additional heat can be produced by shivering.