[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Temperature, exercise and metabolism](https://durgical.com/en/physiology/#s-integrative) › Heat exhaustion and heat stroke

[Physiology](https://durgical.com/en/physiology/) · [Temperature, exercise and metabolism](https://durgical.com/en/physiology/#s-integrative)

# Heat exhaustion and heat stroke

- Mechanism
- Exam priority: medium

In great heat and effort the body loses water and salt; if it can no longer cool down, temperature climbs out of control and damages organs.

Updated 2026-11-01

Also called: Hyperthermia, Heat illness

**See it in 3D:** [Skin](https://durgical.com/en/anatomy/skin/) · [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Key points

- Heat stroke = core temperature >40 °C + CNS dysfunction (confusion, seizures, coma).
- Classic (older adults, heat waves): skin often dry. Exertional (young people exercising): sweating may persist.
- Heat exhaustion: temperature
- Environmental and muscle heat load the body; the hypothalamus dilates skin vessels and turns on sweating.
- Sweat (up to 1–2 L/h) removes water and sodium: plasma volume and preload fall.
- To hold blood pressure, cardiac output cannot supply skin and muscle at once: skin flow falls and cooling capacity is lost.
- Core temperature rises; above ≈40–42 °C proteins and membranes are directly damaged.
- Gut ischemia lets endotoxin through; cytokines and endothelial injury lead to multi-organ failure.

### Starling forces along a capillary

**Arteriolar NFP** +4 mmHg **Venular NFP** −13 mmHg **Filtration** 0.5 **Reabsorption** 5.0 **Net absorption** 4.5 a.u.

Dehydration: the blood is concentrated (↑ πc) and Pc falls: absorption wins and fluid moves from the interstitium into the plasma (the same happens after a hemorrhage).

Tap a force (Pc, πc, Pif, πif), the lymph or the net pressure value.

- Filtration (fluid out)
- Absorption (fluid in)
- Net filtration pressure
- Normal net pressure
- Lymphatic (returns the excess)
- Edema

Heat dehydration lowers capillary pressure: try «Normal» to compare.

## The spectrum of heat illness

| Condition | Core temperature | Mind | Mechanism |
| --- | --- | --- | --- |
| Heat cramps | Normal | Normal | Sodium lost in sweat |
| Heat syncope | Normal or slightly high | Brief loss of consciousness | Skin vasodilation and venous pooling |
| [Heat exhaustion](https://durgical.com/en/conditions/hypernatraemia/) | 40 °C | Altered | Failed thermoregulation, cell damage |

## Clinical notes

- Antipyretics do not work: the set point is normal; temperature falls only with physical cooling.
- Drinking large volumes of plain water during long efforts can cause hyponatremia.
- Acclimatization (10–14 days) expands plasma volume and makes sweating earlier and less salty.

## Memory aid

«If the mind fails in the heat, it's a stroke»: mental status separates exhaustion from heat stroke.

## Test yourself

Think of the answer, then tap the question to see it.

## Which clinical finding separates heat exhaustion from heat stroke?

Nervous system dysfunction (confusion, seizures, coma) with a core temperature >40 °C defines heat stroke.

## Why does dehydration impair the ability to cool down?

With less plasma volume the heart cannot perfuse skin and muscle together; compensatory skin vasoconstriction cuts heat loss and sweating.

## Why does a soldier with exertional heat stroke in the Llanos pass dark urine and have a high creatinine?

Rhabdomyolysis releases myoglobin, which injures the renal tubule, and hypovolemia lowers renal perfusion: acute kidney injury.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/physiology/heat-exhaustion-and-heat-stroke/)

## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Related topics

- [Body temperature regulation](https://durgical.com/en/physiology/body-temperature-regulation/)
- [Fever](https://durgical.com/en/physiology/fever/)
- [Exercise and training physiology](https://durgical.com/en/physiology/exercise-and-training-physiology/)

## Related conditions

- [Hypernatraemia](https://durgical.com/en/conditions/hypernatraemia/)
- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)
- [Hyponatraemia](https://durgical.com/en/conditions/hyponatraemia/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [Heat emergencies: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000056.htm) (MedlinePlus, US National Library of Medicine, 2026); [24.6 Energy and Heat Balance](https://openstax.org/books/anatomy-and-physiology-2e/pages/24-6-energy-and-heat-balance) (OpenStax (Rice University), 2022); [Dehydration: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000982.htm) (MedlinePlus, US National Library of Medicine, 2026); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 74). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/physiology/heat-exhaustion-and-heat-stroke/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/heat-exhaustion-and-heat-stroke/