Environmental Pathology
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Direct answer
Heat stroke, the deadliest environmental emergency, is a core temperature above 40°C with central nervous system dysfunction and, in the classical form, loss of sweating; it kills through a systemic inflammatory response with rhabdomyolysis, disseminated intravascular coagulation and acute kidney injury. Cold injury spans frostbite, in which ice crystals and endothelial damage destroy the extremity, to non-freezing immersion injury. Hypobaric hypoxia at altitude drives pulmonary vasoconstriction and high-altitude pulmonary oedema, while ionising radiation acts through DNA double-strand breaks, producing deterministic effects above a dose threshold and stochastic effects such as carcinogenesis for which no threshold exists.
What you must remember
- Heat spectrum: heat cramps (salt and water loss, core temperature normal), heat exhaustion (volume depletion, sweating preserved, temperature below 40°C), heat stroke (above 40°C, CNS dysfunction, multi-organ failure).
- Cold injury: frostbite — ice crystals, endothelial injury, rapid rewarm in warm water; trench or immersion foot — prolonged wet non-freezing cold, macerated anaesthetic extremity.
- Altitude: hypoxic pulmonary vasoconstriction raises pulmonary artery pressure — high-altitude pulmonary oedema typically within the first days above about 2500–3000 metres; acclimatisation raises ventilation, erythropoietin and 2,3-BPG.
- Chronic hypoxia: excessive polycythaemia (Monge disease), right ventricular hypertrophy, and in the fetus of diabetic or hypoxic mothers different changes again — keep altitude and fetal hypoxia separate in vivas.
- Electrical injury: heat generated along the current path (joule heating), deep muscle necrosis under innocuous-looking skin, alternating current triggers ventricular fibrillation; lightning causes instantaneous massive current with superficial ferning burns.
- Radiation deterministic effects (threshold dose exists): bone marrow suppression, skin erythema, cataract, sterility, teratogenesis, vascular fibrosis.
- Radiation stochastic effects (no threshold): carcinogenesis and germline mutation; risk rises with dose but severity does not.
- Acute radiation syndromes by whole-body dose: haematopoietic at roughly 2–10 Gy (weeks — marrow failure), gastrointestinal above about 10 Gy (days — crypt denudation, sepsis), cerebrovascular above roughly 20–30 Gy (hours — cerebral oedema, seizures, invariably fatal).
Triage of a radiation accident
A practical way to hold radiation biology is to walk through an exposed worker. In the first hours comes the prodrome — nausea, vomiting, fatigue whose onset time crudely tracks dose. The most useful early laboratory test is the serial absolute lymphocyte count, because lymphocytes are among the most radiosensitive cells in the body: a rapid fall to under about 1.0 × 10⁹ per litre within the first day or two signals a significant whole-body dose, and a steep fall toward 0.5 × 10⁹ or below implies the haematopoietic syndrome with its weeks-latent window of infection and bleeding. The count is repeated every few hours to plot the slope, which correlates with dose better than any single value.
The next reasoning step is anatomical. Marrow and lymphoid tissue die first, then the small intestinal crypts (denuding the mucosa and handing the lumen to bacteria), then skin, then vessels; neurons and muscle are relatively resistant, which is why the cerebrovascular syndrome needs the highest dose — the neurons themselves survive longer than the vasculature feeding them. Management follows the syndrome: isolation, transfusion and antimicrobials carry the haematopoietic patient across the weeks until marrow recovers; radioiodine exposure calls for stable iodine to block thyroid uptake — the Chernobyl accident produced a wave of papillary thyroid carcinoma in exposed children.
Where students slip
Two heat traps recur. First, students wait for anhidrosis before diagnosing heat stroke — true in the classical elderly form, but exertional heat stroke in a marathon runner or a recruit on a parade ground can present drenched in sweat with a core temperature of 41°C; the temperature plus altered behaviour makes the diagnosis, and the treatment is immediate evaporative or ice-water cooling, not antipyretics, which have no role. Second, the deterministic-stochastic split gets reversed in writing: cataract and sterility are deterministic (threshold, severity rises with dose), cancer is stochastic (no threshold, probability rises with dose) — an examinee who writes "cancer needs a threshold dose" loses the mark.
Frequently asked questions
What core temperature defines heat stroke?
Above 40°C with central nervous system dysfunction — confusion, seizures or coma; sweating is lost in the classical form but may persist in exertional heat stroke.
Why does high-altitude pulmonary oedema develop?
Hypoxic pulmonary vasoconstriction raises pulmonary artery pressure and capillary stress, producing a high-permeability leak; it typically appears within the first few days above about 2500–3000 metres and descends the patient.
Which acute radiation syndrome follows a whole-body dose of about 8 Gy?
The haematopoietic syndrome — marrow failure with infection and bleeding after a latent period of weeks; 8 Gy is close to the lethal range without intensive support.
Which cells are most sensitive to ionising radiation?
Lymphocytes, followed by haematopoietic precursors and intestinal crypt cells; hence the serial lymphocyte count used as early biodosimetry.
Which cancer rose sharply in children after Chernobyl?
Papillary thyroid carcinoma, driven by radioiodine uptake in the paediatric thyroid.