Vasoconstriction and Vasodilation (Higher tier)

1. 1 State [1 mark]

   State what is meant by vasodilation.

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   Model answer

   The widening of the blood vessels in the skin.

   Mark scheme

   • Widening of blood vessels — 1 mark
2. 2 Describe [2 marks]

   Describe what happens to the blood vessels in the skin when the body is too cold.

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   Model answer

   The blood vessels in the dermis get narrower, which is vasoconstriction, so less blood flows near the surface of the skin.

   Mark scheme

   • Vessels get narrower — 1 mark
   • Less blood flows near the surface — 1 mark
3. 3 Explain [3 marks]

   Explain how vasodilation helps to cool the body.

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   Model answer

   The blood vessels in the skin get wider, so more blood flows close to the surface of the skin. More heat is transferred from the blood to the surroundings, so the body cools.

   Mark scheme

   • Vessels get wider — 1 mark
   • More blood near the surface — 1 mark
   • More heat lost to the surroundings — 1 mark
4. 4 Explain [3 marks]

   Explain why the skin of the fingers of a person outside in the snow looks paler than normal.

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   Model answer

   The hypothalamus detects that the body is cold, and vasoconstriction takes place. The blood vessels in the skin narrow, so less blood flows near the surface, which makes the skin look paler.

   Mark scheme

   • Vasoconstriction — 1 mark
   • Vessels narrow — 1 mark
   • Less blood near the skin surface — 1 mark
5. 5 Explain [4 marks]

   Explain the role of the hypothalamus in controlling the diameter of the blood vessels in the skin.

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   Model answer

   The hypothalamus has receptors that detect the temperature of the blood. If the temperature changes from normal, it sends impulses to the muscles in the walls of the blood vessels in the skin. In the cold, they contract and the vessels narrow, and when it is hot they relax and the vessels widen. The change in heat loss brings the temperature back to normal.

   Mark scheme

   • Detects the temperature of the blood — 1 mark
   • Sends impulses to the muscles in the vessel walls — 1 mark
   • Muscles contract or relax, changing the diameter — 1 mark
   • Heat loss changes, so the temperature returns to normal — 1 mark
6. 6 Evaluate [6 marks]

   A person goes from a warm room into snow. Explain how the body responds to prevent the body temperature from falling.

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   Model answer

   Temperature receptors in the skin detect the cold, and the hypothalamus detects that the temperature of the blood has fallen. The hypothalamus sends impulses to the effectors. The muscles in the walls of the blood vessels in the dermis contract, so the vessels narrow. This is vasoconstriction, and it reduces the blood flow near the surface of the skin, so less heat is lost. The skeletal muscles shiver, and respiration in the muscle cells releases heat, which warms the blood. The sweat glands release little sweat, so less heat is lost by evaporation. As the body temperature rises back towards 37 °C, the signals from the hypothalamus are reduced. The responses reverse the change, which is negative feedback.

   Mark scheme

   • Hypothalamus detects the fall — 1 mark
   • Impulses sent to effectors — 1 mark
   • Vasoconstriction reduces heat loss — 1 mark
   • Shivering releases heat from respiration — 1 mark
   • Less sweat — 1 mark
   • Negative feedback restores 37 °C — 1 mark

Quick check

1. 1

   What is vasoconstriction?

   1. AThe widening of the blood vessels
   2. BThe narrowing of the blood vessels in the skin
   3. CThe release of sweat
   4. DThe movement of hairs
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   B: The narrowing of the blood vessels in the skin

   The narrowing of the blood vessels in the skin.

2. 2

   When does vasodilation happen?

   1. AWhen the body is too hot
   2. BWhen the body is too cold
   3. CWhen the body is asleep
   4. DWhen the body is hungry
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   A: When the body is too hot

   When the body is too hot.

3. 3

   What does vasodilation do to heat loss?

   1. AIt stops heat loss
   2. BIt has no effect
   3. CIt increases heat loss
   4. DIt reduces heat loss
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   C: It increases heat loss

   It increases heat loss.

4. 4

   What controls the muscles in the walls of the blood vessels?

   1. AInsulin
   2. BGlucagon
   3. CSweat
   4. DImpulses from the hypothalamus
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   D: Impulses from the hypothalamus

   Impulses from the hypothalamus.

5. 5

   Why does the skin look red during vasodilation?

   1. AThe skin makes more melanin
   2. BMore blood flows near the surface
   3. CLess blood flows near the surface
   4. DThe sweat is red
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   B: More blood flows near the surface

   More blood flows close to the surface.

6. 6

   Why does the skin look pale during vasoconstriction?

   1. ALess blood flows near the surface
   2. BMore blood flows near the surface
   3. CThe skin is thicker
   4. DThe hairs stand up
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   A: Less blood flows near the surface

   Less blood flows close to the surface.

7. 7

   Which response warms the body in the cold?

   1. AVasodilation
   2. BSweating
   3. CShivering
   4. DHairs lying flat
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   C: Shivering

   Shivering releases heat from respiration.

8. 8

   How is most heat lost from the skin in vasodilation?

   1. AIt is made by the skin
   2. BIt is stored in fat
   3. CIt is carried by the nerves
   4. DIt is transferred from the blood to the surroundings
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   D: It is transferred from the blood to the surroundings

   Heat is transferred from the blood to the surroundings.

9. 9

   What type of control is shown by these responses?

   1. APositive feedback
   2. BNegative feedback
   3. CNo feedback
   4. DRandom control
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   B: Negative feedback

   Negative feedback.