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The body temperature of a healthy person varies during the day by about 0.5 °C (0.9 °F) with lower temperatures in the morning and higher temperatures in the late afternoon and evening, as the body's needs and activities change. [15]
Simplified control circuit of human thermoregulation. [8]The core temperature of a human is regulated and stabilized primarily by the hypothalamus, a region of the brain linking the endocrine system to the nervous system, [9] and more specifically by the anterior hypothalamic nucleus and the adjacent preoptic area regions of the hypothalamus.
An ostrich can keep its body temperature relatively constant, even though the environment can be very hot during the day and cold at night. Koalas also can behaviorally thermoregulate by seeking out cooler portions of trees on hot days. They preferentially wrap themselves around the coolest portions of trees, typically near the bottom, to ...
Conversely, a rise in body temperature (which can be affected by a room's ambient temperature) signals the body to wake up. Therefore, maintaining a cool room can help promote better sleep.
Sufficient stress from extreme external temperature may cause injury or death if it exceeds the ability of the body to thermoregulate. Hypothermia can set in when the core temperature drops to 35 °C (95 °F). [2] Hyperthermia can set in when the core body temperature rises above 37.5–38.3 °C (99.5–100.9 °F).
For instance, core body temperature in humans varies during the course of the day (i.e. has a circadian rhythm), with the lowest temperatures occurring at night, and the highest in the afternoons. Other normal temperature variations include those related to the menstrual cycle .
Many types of animals are classified as being diurnal, meaning they are active during the day time and inactive or have periods of rest during the night time. [1] Commonly classified diurnal animals include mammals, birds, and reptiles. [2] [3] [4] Most primates are diurnal, including humans. [5]
[25] [37] Sleepiness increases during the night. REM sleep occurs more during body temperature minimum within the circadian cycle, whereas slow-wave sleep can occur more independently of circadian time. [33] The internal circadian clock is profoundly influenced by changes in light, since these are its main clues about what time it is.