7.5 - Blood vessels

Question 1

Size comparison of venules and veins - walls and muscles

Answer 1

Venules are smaller than veins. They have very thin walls, and very little smooth muscle. Both venules and veins have valves.

Question 2

Valves in the veins structure compared to valves in the heart

Answer 2

The pocket valves in veins are similar in structure to valves in the heart, but pocket valves are the only type of valve controlled by skeletal muscle.

Question 3

Veins and venules function and adaptations

Answer 3

Veins are adapted to carry blood towards the heart at low pressure.

Adaptations of veins:

1. Collagen- Provides strength to prevent the vessel from bursting and maintain vessel shape.
2. Little smooth muscle and elastic fibre- Not much is needed due to low blood pressure, and thinner walls allow veins to be easily compressed, aiding the flow of blood.
3. Valves- Pocket valves shut to prevent the backflow of blood when veins are squeezed by surrounding skeletal muscle.

Question 4

What are capillaries and adaptations of them?

Answer 4

Capillaries form extensive networks between arterioles and venules, providing an area between blood and tissues where exchange of substances like gases and nutrients can occur.

Adaptations of capillaries:
1. Lumen is very narrow- This allows red blood cells to be close to body cells.
1. Walls are thin- Substances can be exchanged across a short distance by diffusion.
1. Highly branched- This provides a large surface area for diffusion.

Question 5

Main type of blood vessels (5)

Answer 5

1. Arteries- Carry blood away from the heart.
2. Arterioles- Carry blood from arteries into capillaries.
3. Capillaries- Site of diffusion between blood and body tissues.
4. Venules- Carry blood from capillaries into veins.
5. Veins - Return blood to the heart.

Question 6

How is blood flow controlled in the arteries?

Answer 6

• Vasoconstriction- Smooth muscle contracts, constricting the blood vessel and decreasing blood flow.
• Vasodilation - Smooth muscle relaxes, dilating the blood vesseland increasing blood flow.

Question 7

What do arteries do and how are they adapted?

Answer 7

Arteries are adapted to carry blood at high pressure away from the heart.

Adaptations of arteries:

1. Collagen- Provides strength to prevent the vessel from bursting and to maintain vessel shape.
2. Elastic fibres- Contain elastin that lets them stretch and recoil to minimise changes in pressure.
3. Thick smooth muscle layer- Contracts/relaxes to constrict/dilate the lumen and control blood flow.

Arterioles are smaller than arteries, but with a comparatively larger lumen. Their walls have more smooth muscle and less elastin as they do not need to withstand such high pressures.