Respuesta :
Simply put, thermogenesis is the process of producing heat. Enderthermic (warm-blooded) creatures generate heat to keep themselves warm in the cold. Under many circumstances, normal metabolism may generate adequate heat, especially with sufficient thermal insulation (fur or feathers and fat layers). However, when the temperature drops, these creatures (including ourselves) produce heat by "wasteful" behaviors, or actions that use energy but have no "useful" by-products or effects other than the heat they create. Shivering and non-shivering thermogenesis are the two types of thermogenesis. The continual contraction of skeletal muscles that causes shivering causes the body to rapidly vibrate instead of moving in any meaningful ways. Even when no beneficial activity is accomplished, it still requires energy to achieve that, and that energy manifests as heat. You're referring to non-shivering thermogenesis, which for a very long time was only linked to a certain type of fat called brown adipose tissue. The mitochondria in this tissue contain a lot of a unique protein called thermogenin or uncoupling protein (UCP-1). This protein decouples electron transport from ATP synthesis by allowing the proton gradient created across the mitochondrion membrane to seep out. Therefore, in the absence of ATP production, all of the metabolic energy in these cells is "lost" as heat. Of course, the goal is to produce heat, so it is not at all lost. Today, it is understood that muscles are capable of non-shivering thermogenesis as well, this time via obstructing Ca++ transport across sarcoplasmic membranes. A change in the transport causes ATP energy to be used up but little to no Ca++ transfer to take place. Yet another "wasted" process that generates essential heat.
