Mammals maintain homeostasis through both structural protections and the control of various systems through the nervous and endocrine systems. Homeostasis is the maintenance of a constant internal environment, which in mammals and birds includes a consistent temperature. Multiple factors, including chemical and physical factors, are maintained by all animals in order for their body systems to operate with maximum efficiency.
The muscular system is a major element of homeostasis in mammals. Along with the skeletal system, it maintains posture and body structure and protects the internal organs. It is also the main generator of heat for temperature homeostasis. In addition to its structural and support roles, the skeletal system acts as a reservoir of calcium, which the body releases in response to parathyroid hormone. The skeletal system is also the major site of blood cell production, keeping the properties of blood in a constant state. The skin is the outermost protective layer, which excludes unwanted objects and substances and prevents water loss. It also helps maintain temperature homeostasis in many mammals by excreting sweat through pores contained within it.
Chemical homeostasis must be maintained, and this requires the constant removal of metabolic wastes so they do not build up in the body's tissues. This is accomplished via the circulatory system, which carries these wastes to the excretory system for elimination.