Hypothalamic Set Point and Fever
- Skin temperature sensors relay temperature information to the anterior hypothalamus.
- Hypothalamic temperature sensors relay core temperature information to the anterior hypothalamus.
- Anterior hypothalamus compares core temperature with the hypothalamic set point.
- Core temperature below the set point activates posterior hypothalamic responses.
- Posterior hypothalamus increases metabolism when core temperature is below the set point.
- Posterior hypothalamus activates shivering when core temperature is below the set point.
- Posterior hypothalamus activates cutaneous vasoconstriction when core temperature is below the set point.
- Core temperature above the set point activates anterior hypothalamic responses.
- Anterior hypothalamus activates cutaneous vasodilation when core temperature is above the set point.
- Anterior hypothalamus stimulates sweat glands through sympathetic output when core temperature is above the set point.
- Pyrogens raise the hypothalamic set point.
- Phagocytes produce interleukin-1.
- Interleukin-1 acts on the anterior hypothalamus.
- Interleukin-1 increases prostaglandin production in the anterior hypothalamus.
- Prostaglandins raise the hypothalamic set point.
- Raised hypothalamic set point initiates heat-generating responses.
- Fever results when pyrogen-driven set point elevation triggers heat-generating responses.
- Aspirin reduces fever by inhibiting cyclooxygenase.
- Cyclooxygenase inhibition reduces prostaglandin production.
- Reduced prostaglandin production lowers the hypothalamic set point.
- Lowered hypothalamic set point activates sweating and vasodilation.
- Steroids reduce fever by blocking arachidonic-acid release from brain phospholipids.
- Pyrogens are fever-producing signals, interleukin-1 is an immune signaling molecule, prostaglandins are lipid-derived signaling molecules, and cyclooxygenase is an enzyme needed for prostaglandin production.
- Reduced arachidonic-acid release decreases prostaglandin production.
- Heat exhaustion results from excessive sweating.
- Heat exhaustion involves reduced blood volume.
- Heat exhaustion involves reduced arterial pressure.
- Heat exhaustion may cause syncope.
- Heat stroke occurs when body temperature rises enough to damage tissues.
- Heat stroke occurs when sweating fails to remove heat adequately.
- Hypothermia occurs when cold exceeds the capacity of shivering and metabolic heat production.
- Malignant hyperthermia occurs in susceptible individuals after exposure to inhaled anesthetics.
- Malignant hyperthermia causes a massive increase in skeletal-muscle oxygen consumption.
- Malignant hyperthermia causes a massive increase in skeletal-muscle heat production.
- Malignant hyperthermia causes a rapid rise in body temperature.
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