3. blood circulation (vessels)

ARTERIES

• carry blood away from heart to cells of body

• almost all arteries carry oxygenated blood

ARTERIES- EXCEPTIONS

• pulmonary artery- carry deoxygenated blood from heart to lungs

• umbilical artery- during pregnancy, carry deoxygenated blood from fetus to placenta

ARTERIAL SYSTEM

• arteries leaving heart branch off in every direction, and diameter of lumen (central space inside blood vessel) gets smaller the further it is from heart

• very smallest branches of arterial system, furthest from heart, are arterioles

ARTERIES- DIAGRAM

ARTERIES- LAYERS

• elastic fibres allow vessels to stretch then recoil– vessels can accommodate a greater vol of blood w/out being damaged

• helps as pressure surges in vessels as heart beats

• between surges recoil of elastic fibres squeezes blood and keeps it flowing

• collagen fibres provide general strength/support so that vessels don’t burst and allow flexibility- can be found in middle and outer layer

PERIPHERAL ARTERIES/ARTERIOLES

• small arteries further away from heart

• have the same basic structure as other arteries except…

  • have a greater proportion of smooth muscle in relation to size which allows constriction of lumen to restrict blood flow into capillaries supplying tissues with blood (vasoconstriction)

  • have a smaller proportion of elastic fibres in relation to size bc blood pressure is lower

VEINS

• carry blood back towards heart

• most veins carry deoxygenated blood

VEINS- EXCEPTIONS

• pulmonary vein- carry oxygenated blood from lungs back to heart

• umbilical vein- during pregnancy, carry oxygenated blood from placenta to fetus

VEINS- DIAGRAM

VEINS- CHARACTERISTICS

• hold large vol of blood

• low blood pressure in veins- blood surges from heart are eliminated as blood passes from capillary beds

• this blood at low pressure must be returned to heart to be oxygenated again and recirculated

VEINS- VALVES

• when blood moves in right direction, valve (semilunar) is forced open

• but if blood tries to flow in wrong direction, it gets trapped in curved ‘doors’ of valve, closing the valve (prevents backflow)

• many larger veins are surrounded by skeletal muscle– when we move our arms/legs muscles contract and squeeze veins, helping force blood through in right direction

CAPILLARIES

• capillaries branch between cells- no cell is far from capillary, so substances can diffuse between cells and blood quickly

• small diameter- blood travels slowly through them- gives more opportunity for diffusion to occur

• smallest capillary no wider than single red blood cell

CAPILLARIES- ADAPTATIONS

• thin walls (one cell thick) and contain no elastic fibres, smooth muscle or collagen- helps fit between individual cells and allows rapid diffusion of substances between blood and cells

• O2 and other molecules quickly diffuse out of blood in capillaries into body cells

• CO2 and other waste molecules diffuse in

• blood entering capillary network from arteries is oxygenated- by time it leaves, carries less O2 and more CO2

CAPILLARIES- DIAGRAM

GRAPHS AND BLOOD VESSELS

• velocity (A)

  • highest in arteries as blood pumped out of heart at high pressure so travels faster

  • lowest in capillaries as these vessels are so narrow and offer most resistance

  • velocity increases in veins as they are wider so offer less resistance than capillaries

• cross-sectional area (C)

  • highest in capillaries as these vessels are the most numerous by far– thus providing a large SA for diffusion

• permeability (D)

  • highest in capillaries as walls are only one cell thick so diffusion pathway is short

  • other vessels are not permeable

• pressure (B)

  • highest in arteries since these lead out of the heart

  • pressure fluctuates in arteries w/ every beat due to elastic nature of arteries

  • pressure decreases further away from heart the blood goes