Overview
This lecture covers thermoregulation, focusing on how the body maintains core temperature, associated mechanisms, populations at risk, and specific conditions such as fever, hyperthermia, and hypothermia.
Thermoregulation Concepts
- Thermoregulation is the process of maintaining a constant core body temperature.
- The hypothalamus is the main thermal control center, regulating body temperature via neurological and hormonal responses.
- Infection often causes fever and chills due to altered thermoregulation.
- Perfusion, skin integrity, and fluid/electrolyte balance influence heat retention/loss.
- Malnutrition increases the risk of hypothermia due to reduced heat production.
Core Body Temperature and Regulation
- Core temperature (internal organs) is normally 97–99.5°F (average ~98.6°F), with daily variation.
- Heat production results from metabolism, muscle activity, hormones, and neurotransmitters like epinephrine.
- Heat loss primarily occurs at the skin via radiation, conduction, convection, and evaporation.
- Arteriovenous anastomoses under the skin control heat dissipation or retention.
- Pyloerection (goosebumps) helps conserve heat.
Mechanisms of Heat Loss
- Radiation: transfer of heat through air/vacuum (e.g., sun exposure).
- Conduction: direct heat movement between molecules or surfaces.
- Convection: heat transfer via air currents replacing warm air at the body surface.
- Evaporation: body heat converts skin water to vapor, cooling the body.
Populations at Risk
- Infants/young children lose heat easily due to high surface area and limited fat.
- Elderly have decreased temperature regulation from fewer/less efficient sweat glands.
- People in extreme climates and those with low socioeconomic status are more vulnerable to temperature extremes.
Fever vs Hyperthermia
- Fever (pyrexia) is a hypothalamus-controlled rise in temperature, usually in response to infection or pyrogens.
- Fever involves movement of the hypothalamic set point upward; shivering and vasoconstriction follow to raise core temperature.
- Hyperthermia is increased body temperature (>37.6°C) without a change in hypothalamic set point; often from heat exposure or excessive muscle exertion.
- Malignant hyperthermia is uncontrolled skeletal muscle contraction, often triggered by anesthesia.
Hypothermia
- Hypothermia results from excessive heat loss, insufficient heat production, or overwhelming of hypothalamic control.
- Primary hypothalamic dysfunction is rare in hypothermia.
Key Terms & Definitions
- Thermoregulation — maintenance of a stable core body temperature.
- Core body temperature — temperature of internal organs, typically 97–99.5°F.
- Hypothalamus — brain region controlling temperature set point.
- Fever (Pyrexia) — elevation of body temperature due to upward hypothalamic set point shift.
- Hyperthermia — abnormally high body temperature without hypothalamic set point adjustment.
- Malignant Hyperthermia — severe, rapid rise in body temperature and muscle rigidity, often anesthesia-induced.
- Hypothermia — abnormally low body temperature from heat loss/production imbalance.
Action Items / Next Steps
- Review the mechanisms and differences between fever and hyperthermia.
- Prepare for discussion on clinical manifestations of hypothalamic dysfunction in the next class.