4.8.3Additional lessons
Thermoregulation — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 131 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Control Pathway
1
Thermoreceptors in the skin detect the temperature of the surroundings, and others monitor the temperature of blood.
2
The hypothalamus in the brain receives impulses and compares the temperature with the set point near 37 °C.
3
If the temperature has moved away from the set point, the hypothalamus sends nerve impulses to effectors.
4
Effectors in the skin and muscles change heat loss or heat production.
5
Core temperature returns to the set point and the response fades by negative feedback.
Part 2 of 5Responses to Cold
Vasoconstriction
- Vasoconstriction Arterioles supplying skin capillaries narrow, so less blood flows near the surface and less heat is lost.
Shivering
- Shivering Rapid involuntary muscle contractions release heat from respiration.
Hair erection
- Hair erection Hair erector muscles raise body hairs, trapping an insulating layer of air.
Sweating stops
- Sweating stops Sweat glands become less active, so less heat is lost by evaporation.
Brown fat
- Brown fat Brown adipose tissue can release heat through non-shivering thermogenesis, especially in infants.
Part 3 of 5Responses to Heat
Vasodilation
- Vasodilation Skin arterioles widen, so more blood flows near the surface and heat is lost by radiation.
Sweating
- Sweating Sweat glands secrete sweat, and evaporation of water from the skin removes heat.
Hairs flat
- Hairs flat Hair erector muscles relax, so hairs lie flat and trap less air.
Behaviour
- Behaviour Moving into shade, removing clothing and drinking cold water also help lower temperature.
| Response | Too cold | Too hot |
|---|---|---|
| Arterioles | Vasoconstriction | Vasodilation |
| Sweat | Reduced | Increased |
| Muscles | Shivering | No shivering |
Part 4 of 5Why Temperature Control Matters
Why Temperature Control Matters
Enzymes
- Enzymes Too low a temperature slows enzyme reactions; too high a temperature can denature enzymes.
Efficiency
- Efficiency A stable temperature keeps metabolism predictable, regardless of the surroundings.
Endotherms
- Endotherms Humans generate heat internally from metabolism, which allows activity in cold conditions but needs a high energy intake.
Negative feedback
- Negative feedback Both heating and cooling responses end when the temperature returns to the set point.
Part 5 of 5Exam Checklist & Tips
4.8.3 – Key Points for the Exam
- Thermoregulation Control of body temperature within limits.
- Hypothalamus Brain region that acts as the control centre for temperature.
- Vasoconstriction Narrowing of arterioles to reduce blood flow.
- Vasodilation Widening of arterioles to increase blood flow.
- Thermoreceptor Sensory cell that detects temperature.
Common Mistakes
- Saying that capillaries move up and down in the skin; it is arterioles that constrict or dilate.
- Stating that shivering cools the body; it produces heat.
- Saying that the skin controls temperature; the hypothalamus is the control centre.
- Claiming that sweating cools the body because sweat is cold; heat is lost as the water evaporates.
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