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As in other mammals, human thermoregulation is an important aspect of homeostasis. In thermoregulation, body heat is generated mostly in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles. [1] Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid.
The human body has two methods of thermogenesis, which produces heat to raise the core body temperature. The first is shivering, which occurs in an unclothed person when the ambient air temperature is under 25 °C (77 °F) [dubious – discuss]. [18] It is limited by the amount of glycogen available in the body. [5]
Starvation response in animals (including humans) is a set of adaptive biochemical and physiological changes, triggered by lack of food or extreme weight loss, in which the body seeks to conserve energy by reducing metabolic rate and/or non-resting energy expenditure to prolong survival and preserve body fat and lean mass.
This model explaining the development of thermogenesis is older and more widely accepted among evolutionary biologists who study thermogenesis. The second explanation is the "parental care" model. This theory proposes that the convergent evolution of thermogenesis in birds and eutherians is based on shared behavioral traits.
Urinary water loss, when the body water homeostat is intact, is a compensatory water loss, correcting any water excess in the body. However, since the kidneys cannot generate water, the thirst reflex is the all-important second effector mechanism of the body water homeostat, correcting any water deficit in the body.
The human body is the entire structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organs and then organ systems . The external human body consists of a head , hair , neck , torso (which includes the thorax and abdomen ), genitals , arms , hands , legs , and feet .
Energy intake is measured by the amount of calories consumed from food and fluids. [1] Energy intake is modulated by hunger, which is primarily regulated by the hypothalamus, [1] and choice, which is determined by the sets of brain structures that are responsible for stimulus control (i.e., operant conditioning and classical conditioning) and cognitive control of eating behavior.
Approximately all enzymatic reaction in the human body is thermogenic, which gives rise to the basal metabolic rate. [2] In bodybuilding, athletes wishing to reduce body fat percentage use thermogenics in order to attempt to increase their basal metabolic rate, thereby increasing overall energy expenditure.