Blood vessels

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

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

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

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

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)

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. 20/04/2017

Artery and heart disease Healthy artery Unhealthy (clogged) artery 20/04/2017

Artery and heart disease Unhealthy (clogged) artery 20/04/2017