Mechanism of Fever, Cold-Induced Injuries, and Heat Stroke

Pathophysiology of Fever: Role of Pyrogens and Hypothalamic Regulation

Fever is an elevation of body temperature triggered by pyrogens, which activate the hypothalamus to reset the body's thermoregulatory set point. Pyrogens can be endogenous (such as cytokines) or exogenous (such as bacterial endotoxins).

Role of Pyrogens

• Endogenous pyrogens include interleukin-1 (IL-1) and tumor necrosis factor (TNF), which stimulate prostaglandin E2 (PGE2) in the hypothalamus.
• Exogenous pyrogens, such as lipopolysaccharides, indirectly induce fever by promoting cytokine release.

Hypothalamic Regulation

The hypothalamus controls temperature via the preoptic area. When pyrogens stimulate PGE2 production, this leads to an increased set point, initiating mechanisms such as shivering and vasoconstriction to raise body temperature.

Cold-Induced Injuries

Exposure to cold environments can lead to frostbite and hypothermia, affecting tissue integrity and metabolic function.

Frostbite

• Caused by prolonged exposure to freezing temperatures, leading to tissue freezing and necrosis.
• Commonly affects extremities, such as fingers, toes, and ears.

Hypothermia

Occurs when the core temperature drops below 35°C, impairing enzymatic activity and cardiac function.

Heat Stroke

Heat stroke results from excessive heat exposure, overwhelming thermoregulatory mechanisms, and leading to multi-organ dysfunction.

Signs and Symptoms

• Elevated core temperature above 40°C.
• Neurological symptoms such as confusion and unconsciousness.
• Systemic inflammation and potential organ failure.