Explain vasodilation supplying surface capillaries
Identify the controlled arteriole and the conditional heat-loss effect.
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall hormone production and blood transport, respiration, liver storage and electrical impulses along neurones.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which vessel has the controlled smooth-muscle widening?
What you will learn
- Describe arteriole widening
- Connect increased skin flow with heat transfer
Explain vasodilation supplying surface capillaries
| Feature | Meaning |
|---|---|
| Controlled vessel | Arteriole supplying surface capillaries |
| Wall / lumen | Muscle relaxes; lumen widens |
| Surface flow | Increases through the fixed capillary network |
| Condition | Cooler surroundings support outward heat loss |
Describe arteriole widening
Vasodilation in this syllabus account is widening of the arterioles supplying skin surface capillaries. Smooth muscle in the arteriole wall relaxes, increasing its lumen diameter and allowing more blood flow through the surface capillary network. The capillaries themselves do not need to contract or move closer to the surface.
Warm blood carried nearer the skin surface can transfer more heat to surroundings that are cooler than the body. Increased surface blood flow therefore helps increase heat loss in the stated cooler-surroundings model. The temperature difference matters: this is not a claim that increased flow always loses heat regardless of how hot the surroundings are.
Connect increased skin flow with heat transfer
Keep vessel identification and flow effect together. Arterioles supply capillaries, and the controlled smooth-muscle change occurs in the arteriole wall. The drawing represents a wider feeding lumen with an unchanged-position capillary network. It is qualitative, not a measured human artery diameter or a calculation of exact heat loss.
When internal temperature rises above its regulated level, coordinated vasodilation can contribute to correction. As the temperature departure reduces, the increased corrective response diminishes. This mechanism complements sweat evaporation but does not replace it: increased blood flow changes heat transfer, whereas evaporation requires a change of state and energy from the skin.
Pause and explain
When does increased surface flow support outward heat loss in this model?
Worked example
Explain how vasodilation can increase heat loss.
Show the worked solution
- Arteriole smooth muscle relaxes, widening the lumen and increasing surface capillary flow.
- In cooler surroundings, this increases transfer of body heat outwards.
Answer Arterioles supplying skin surface capillaries widen; more blood flows through them, increasing heat loss when the surroundings are cooler than the body.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain vasodilation and its temperature-control effect in cooler surroundings.
Give me a hint
Include controlled vessel, flow and transfer.
Compare my reasoning
- Arteriole wall muscle relaxes and lumen widens.
- More surface capillary flow allows more outward heat transfer.
Arterioles supplying skin surface capillaries widen, increasing surface blood flow and heat loss to cooler surroundings.
Look for these in your work
- Name arterioles
- Connect increased flow and conditional heat loss
Correct: skin capillaries move upwards and contract to lose heat.
Give me a hint
The controlled feeding vessel and mechanism are different.
Compare my reasoning
- Arterioles widen by wall muscle relaxation.
- Surface capillaries remain in position and carry increased flow.
The supplying arterioles widen; surface capillaries stay in position and receive more flow. They do not migrate or contract to cause vasodilation.
Look for these in your work
- Correct the vessel action
- Keep network position fixed
Why should the heat-loss explanation state that surroundings are cooler?
Give me a hint
Heat transfer depends on a temperature difference.
Compare my reasoning
- Outward heat transfer is supported by cooler surroundings.
- A hotter environment cannot be assigned the same outward-loss effect without further analysis.
Cooler surroundings support outward heat transfer. Increased skin flow does not guarantee the same heat-loss effect in surroundings hotter than the body.
Look for these in your work
- State the thermal condition
- Avoid an unconditional heat-loss claim
Common mistakes
- Saying capillaries contract to cause dilation.
- Claiming vessels physically move towards the surface.
What can you explain now?
When does increased surface flow support outward heat loss in this model?
Compare with the explanation
When surroundings are cooler than the body
The temperature difference allows outward transfer.
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Make it stick
Explain vasodilation with the correct vessel and an explicit temperature-difference condition.
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