2 Blood Vessels What are blood vessels? Arteries Veins Capillaries ContentsBlood VesselsWhat are blood vessels?ArteriesVeinsCapillariesSummary activities
3 Blood vessels and the circulatory system The circulatory system is made up of the heart, blood and blood vessels.What are blood vessels and what do they do?Blood vessels are the network of tubes that carry the blood, pumped by the heart, around the body.
4 What is the total length of blood vessels? Make a guess at the total length, in kilometres, of all the blood vessels in an adult human?100, 000 kilometresThat’s more than twice the distance around the Earthat the equator!There are a lot of blood vessels so they must be important.Are all blood vessels the same?
5 Different types of blood vessels There are three types of blood vessels, as shown in this magnified part of the circulatory system.blood from the heartblood to the heartarteryveinWhy are there different types of blood vessels?
6 Different types of blood vessels The different blood vessels have different jobs to do in carrying blood around the body.blood from the heartblood to the heartarteryveincarries blood away fromthe heartcarries blood back intothe heartcarries blood to and from the body’s cellsDo all blood vessels carry the same type of blood?
7 Blood Vessels What are blood vessels? Arteries Veins Capillaries ContentsBlood VesselsWhat are blood vessels?ArteriesVeinsCapillariesSummary activities
8 carries blood away from What is an artery?Arteries are the blood vessels that carry blood away from the heart.blood from the heartblood to the heartcarries blood away fromthe heartarteryBlood that is pumped from the heart to the body’s cells along the arteries is oxygen-rich.Is this oxygen-rich blood under high or low pressure whenit leaves the heart?
9 Cross-section of an artery The arteries carry blood at high pressure away from the heart.Looking at the cross-section of an artery, why is it suitable for carrying blood at high pressure?thick outer wallthick inner layerof muscle andelastic fibresnarrow central tube
10 Blood flow in arteries – high pressure Imagine using a hosepipe and covering half of the open end with your thumb. What happens to the pressure of the water?The water is released under higher pressure and flows faster.In the same way, arteries havea narrow central core and thick muscular walls.This means that blood from the heart is kept at high pressure and flows quickly to reach every part of the body, even the little toes!
11 Blood flow in arteries – stretching With each heartbeat, a surge of blood enters the arteries and they expand to cope with the increased blood flow.Which part of an artery allows it to expand?thick inner layerof muscle andelastic fibresincreasedblood flowThe elastic fibres allow the artery to stretch under pressure. The muscle fibres contract to push the blood along andkeep it flowing.
12 Blood flow in arteries – detecting There is a simple way of detecting how an artery stretches under the pressure of each heartbeat.What is it?You can feel your pulse because of the stretching of an artery that passes between bone and the surface of the skin.
13 Blood Vessels What are blood vessels? Arteries Veins Capillaries ContentsBlood VesselsWhat are blood vessels?ArteriesVeinsCapillariesSummary activities
14 carries blood back into What is a vein?Veins are the blood vessels that carry blood back into the heart.blood from the heartblood to the heartveincarries blood back intothe heartBlood that travels from the body’s cells to the heart along the veins is oxygen-poor.Is this oxygen-poor blood under high or low pressure as it returns to the heart?
15 Cross-section of a vein The veins carry blood at low pressure back into the heart.Looking at the cross-section of a vein, why is it suitable for carrying blood at low pressure?thin outer wallthin inner layerof muscle andelastic fibreswidecentral tube
16 Comparing cross-sections Compare the cross-section of a veinand an artery.Why are they different?Veins do not need to keep blood flowing quickly at high pressure and so they have much thinner walls than arteries.
17 Blood flow in veins – preventing backflow Blood travels back to the heart in veins at low pressure.If the blood pressure is too low, what, for example, might happen to the blood in leg veins?bloodto theheartpossible backflowof bloodgravityIf low-pressure blood has to move against gravity, it mightslow down further and even flow in the wrong direction!
18 Blood flow in veins – valves Veins have valves to prevent backflow.backflowpreventedvein valveopenvein valveclosedblood to the heartWhen blood flows along veins it pushes pastthe valves, which canonly open in one direction.If blood in a vein does flow backwards,it is trapped byclosed valves.
19 Blood flow in veins – muscle contraction Veins have valves to prevent backflow. They also have thin walls and so need help from nearby muscles to push blood towards the heart.How does this work? (Think of a tube of toothpaste!)blood to the heart
20 Blood flow in veins – muscle contraction Many veins are surrounded by muscles. When you move, these muscles contract and squeeze the veins.This pushes blood along the veins back towards the heart. (Just like squeezing a tube of toothpaste!)blood keeps flowingto the heartblood to the heart
21 Blood Vessels What are blood vessels? Arteries Veins Capillaries ContentsBlood VesselsWhat are blood vessels?ArteriesVeinsCapillariesSummary activities
22 What is a capillary? artery vein Capillaries are the tiny blood vessels that carry a blood supply to and from the body’s cells.What blood vessels are linked by capillaries?arteryveinCapillaries link arteries to veins.Capillaries are the only blood vessels where substances can be exchanged between the blood and body cells.
23 Cross-section of a capillary The capillaries carry blood to and from the body’s cells.Looking at the cross-section ofa capillary, why is it suitable for the exchange of substances between the blood and body cells?
24 What happens in a capillary? Capillaries have very thin walls for the exchange of substances between the blood and surrounding body cells.How does this happen?wasteproductsusefulsubstancesSubstances are exchangedby diffusion.Useful substances in the blood diffuse across the capillary wall into body cells.Waste products from the body cells diffuse across the capillary wall into the blood.
25 Gas exchange in a capillary bed A network of capillaries is called a capillary bed.What gases are exchanged by diffusion in a capillary bed?carbondioxideoxygenOxygen in the blood diffuses across the capillary wall into body cells for respiration.Carbon dioxide from the cells diffuses across the capillary wall into the blood.
26 Blood Vessels What are blood vessels? Arteries Veins Capillaries ContentsBlood VesselsWhat are blood vessels?ArteriesVeinsCapillariesSummary activities