4.9.3Additional lessons
Thermoregulation — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 81 of 101
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.
Section 1 of 4Control of Body Temperature
Endotherms
- Endotherms Mammals and birds keep a fairly constant core temperature using heat released by their own metabolism, instead of relying on the environment.
Receptors
- Receptors Thermoreceptors in the skin detect external temperature and others in the hypothalamus detect the temperature of the blood.
Control centre
- Control centre The hypothalamus compares the information with the set point and sends signals to the effectors.
Hormonal route
- Hormonal route The hypothalamus can also trigger release of thyroid-stimulating hormone from the pituitary,
- which causes the thyroid to secrete thyroxine and raise the metabolic rate.
Ectotherms
- Ectotherms Reptiles and amphibians gain most body heat from the surroundings,
- so they control temperature mainly by behaviour such as basking in sun or sheltering in a burrow.
| Feature | Endotherm | Ectotherm |
|---|---|---|
| Main heat source | Own metabolism | Environment |
| Body temperature | Fairly constant | Varies with surroundings |
| Energy needs | High, needs much food | Lower |
Section 2 of 4Responses to Overheating
Responses to Overheating
Vasodilation
- Vasodilation Arterioles in the skin 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 uses up heat energy and cools the body.
Hair flattening
- Hair flattening Erector muscles relax so hairs lie flat, trapping less air and allowing heat to escape more easily.
Behaviour
- Behaviour Moving into shade, resting and drinking help to reduce heat gain and replace lost water.
Section 3 of 4Responses to Cold
Responses to Cold
Vasoconstriction
- Vasoconstriction Arterioles in the skin narrow, reducing blood flow near the surface and cutting heat loss.
Shivering
- Shivering Rapid involuntary contractions of skeletal muscles release heat from respiration.
Hair erection
- Hair erection Erector muscles contract and raise the hairs, which traps an insulating layer of air.
Non-shivering thermogenesis
- Non-shivering thermogenesis Brown adipose tissue oxidises lipids to release heat, which is especially important in newborn infants.
Raised metabolism
- Raised metabolism Thyroxine increases the metabolic rate of cells, and so heat production, over a longer period.
| Response | Too hot | Too cold |
|---|---|---|
| Skin arterioles | Dilate | Constrict |
| Sweat glands | Active | Inactive |
| Skeletal muscle | Normal | Shivering |
| Hairs | Flat | Erect |
Section 4 of 4Exam Checklist & Tips
4.9.3 – Key Points for the Exam
- Thermoregulation The control of internal body temperature within narrow limits.
- Hypothalamus The part of the brain that acts as the thermoregulatory control centre.
- Vasoconstriction Narrowing of blood vessels, reducing blood flow.
- Non-shivering thermogenesis Heat production by brown adipose tissue without muscle contraction.
Common Mistakes
- Saying that blood vessels 'move closer to the skin';
- arterioles dilate and more blood flows through the skin capillaries.
- Claiming that sweating cools the body by itself; the cooling occurs when the sweat evaporates.
- Forgetting that shivering produces heat through respiration in muscle.
- Saying that hairs 'warm' the body; they trap air, which insulates.
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