Thermoregulation: body temperature control
Homeostasis and response • The human nervous system
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Thermoregulatory centre and receptors
A specialised area of the brain acts as the thermoregulatory centre and uses temperature receptors to monitor body temperature. Receptors in the hypothalamus detect the temperature of blood flowing through the brain. Separate receptors in the skin detect external temperature and send impulses to the thermoregulatory centre. The centre integrates these signals and sends electrical impulses to effectors to produce appropriate responses . Temperature control uses negative feedback. A change away from the set point causes the centre to trigger mechanisms that move temperature back toward the set point. The process is automatic and rapid when mediated by the nervous system, because signals travel as electrical impulses along neurones to muscles and glands .
Mechanisms that lower body temperature
Vasodilation increases blood flow to capillaries near the skin surface. Arteriole muscles relax, arterioles dilate, and more warm blood reaches the skin. Increased surface blood flow raises heat transfer to the environment by radiation, conduction and convection, producing cooling of core temperature . Sweating increases heat loss by evaporation. Sweat glands secrete a watery fluid onto the skin surface. The evaporation of this fluid absorbs thermal energy from the skin, lowering body temperature. Large sweat rates require fluid replacement to avoid dehydration. Together, vasodilation and sweating reduce body temperature when the thermoregulatory centre detects overheating .
Mechanisms that raise body temperature
Vasoconstriction reduces blood flow to the skin. Arteriole muscles contract, narrowing arterioles and diverting warm blood away from the skin surface. Reduced skin blood flow lowers heat loss and helps conserve core heat for vital organs . Shivering is involuntary rapid contraction and relaxation of skeletal muscles. Muscle contractions increase cellular respiration and release thermal energy, raising body temperature. Shivering consumes glucose and causes fatigue if prolonged. Both vasoconstriction and shivering activate when the thermoregulatory centre detects a fall in core or skin temperature .
Contextual application: exercise, cold exposure and fever (HT)
During vigorous exercise, metabolic heat production increases. The thermoregulatory centre responds to rising blood temperature by increasing vasodilation and sweat production to dissipate excess heat. Increased skin blood flow plus sweat evaporation maintain core temperature during activity but increase fluid loss and risk of dehydration . During cold exposure, core temperature falls and the thermoregulatory centre triggers vasoconstriction to conserve heat and shivering to generate additional heat. If thermoregulatory responses prove insufficient the body progresses to hypothermia. Fever raises the set point in the brain; the centre then produces heat‑generating responses (shivering, vasoconstriction) to reach the higher set point until the fever subsides or treatment intervenes .
Limits and failure of thermoregulation
Thermoregulatory mechanisms have physiological limits. Extreme ambient temperatures, high humidity (which reduces evaporation), dehydration, or prolonged exertion can overwhelm cooling mechanisms, causing hyperthermia. Core temperatures above about 38.5 °C impair enzyme function and risk organ failure. Conversely, prolonged cold exposure can overwhelm heat‑generating responses and lead to hypothermia below about 35 °C with confusion and organ failure . External factors such as clothing, wind chill, body surface area and age alter effectiveness of responses. Children and older adults show reduced thermoregulatory efficiency. Hydration status and metabolic rate also influence the capacity to produce or lose heat.
Key notes
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