1. Blood vessels

2. Arteries
Thick muscular walls which can contract and relax to squeeze blood along artery
Small lumen
No valves
Carries oxygenated blood (except pulmonary artery) at high pressure away from the heart

3. Veins
Large lumen
Have valves to prevent back flow of blood as pressure is low and blood is flowing against gravity
Carries deoxygenated blood (except pulmonary vein) at low pressure in towards the heart

4. Capillaries One cell thick vessels
Blood changes from oxygenated to deoxygenated
Transported substances enter and leave the blood here – i.e. substances are exchanged through capillary beds
Large surface area – rapid exchange of materials

5. Functions of blood vessels
Arteries – carry blood away from the heart
Veins – carry blood into the heart
Capillaries – exchange surfaces between body cells & blood
Arterioles – connects arteries to capillaries & regulates blood flow into capillary beds
Venules – connects capillaries to veins

7. Veins Capillaries Arteries Function
carry blood from tissues to the heart
allow exchange of materials between the blood and the tissues
carry blood from the heart to the tissues
Structure of walls
Thin walls, since blood at low pressure
Very thin, permeable walls, only one cell thick to allow exchange of materials
Thick walls with smooth elastic layers to resist high pressure and muscle layer to aid pumping
Lumen size
Large lumen to reduce resistance to flow.
Very small lumen. Blood cells must distort to pass through.
Small lumen
Valves
Many valves to prevent back -flow
No valves
No valves (except in heart)
Pressure & blood flow
Blood at low pressure; flow is slow
Blood pressure falls in capillaries; flow is slow
Blood at high pressure; flow is fast
Type of blood
Usually deoxygenated (except in pulmonary vein)
Changes from oxygenated to deoxygenated (except in lungs)
Usually oxygenated (except in pulmonary artery)

8. Summary: arteries, veins and capillaries
Capillaries have thin walls (one cell thick) to allow glucose and oxygen to pass through. They connect arteries to veins.
Arteries carry high pressure blood away from the heart. They have smaller lumen and no valves. They have thick walls made from muscle and elastic fibres.
“Lumen”
Veins carry low pressure blood in to the heart. They have thinner, less elastic walls and have valves to prevent blood going backwards.
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9. Artery and heart disease
Healthy artery
Unhealthy (clogged) artery
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10. Artery and heart disease
Unhealthy (clogged) artery
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