The environment around us is continually changing and poses difficulties for the body to carry out its internal processes. Homeostasis is the maintenance of a constant internal environment within the body regardless of changes in either external or internal conditions. It allows a certain degree of independence from the environment.
Regulating body temperature is one instance where homeostasis occurs (Thermoregulation). Some methods are conduction, where the body absorbs/removes heat via contact surfaces; convection, which is the upward flow of warm air or the downward flow of cold air past the body; radiation, where heat is transferred/received via infrared waves on non-contact surfaces; evaporation where water on the body is evaporated giving a cooling effect.
To maintain a constant body temperature feedback is needed. There are 3 types of feedback which are negative, positive and feedforward information. Negative feedback suggests that the process should be reduced, positive feedback tells the system to increase a response and feedforward information tells the system to change the set-point.
In hot weather, a range of other processes occur which are more specific than the ones described above. There is an increase in sweat production. Vasodilation occurs (arterioles near the skin dilate and shunt vessels constrict. More blood travels closer to the skin and heat is lost via radiation). Hair erector muscles relax and the hairs lie flat against the body so that there is a less amount of hot air trapped close to the body.
In cold weather, the opposite occurs. Vasoconstriction occurs (Shunt vessels dilate and arterioles close to the skin constrict). Sweat production stops and hair erector muscles contract and hairs stand up trapping a warm layer of air next to the body. The metabolic rate increases and shivering occurs.