7 Cardiac cycle & Blood vessels

  • Created by: lee8444
  • Created on: 11-03-20 11:34

Relaxation of the heart (diastole)

  • Blood returns to the heart via the pulmonary vein and the vena cava
  • As the atria fill, the pressure increases
  • When this pressure exceeds the pressure of the ventricles, the atrioventricular valves open
  • This allows blood to pass through into the ventricles which is aided by gravity
  • All muscular walls of the heart are relaxed
  • Semi-lunar valves are closed
  • 'dub' sound
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Contraction of the atria (atrial systole)

  • Atrial walls contract
  • Ventricle walls are relaxed
  • All remaining blood in the atria is forced into the ventricles
  • This is due ot the increased pressure produced by the contraction
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Contraction of the ventricles (ventricular systole

  • After a short delay after atrial systole
  • Ventricles are allowed to fill with blood
  • Walls contract simultaneously
  • this increases the pressure inside the ventricles shutting the atrioventricular valves which prevents backflow
  • 'lub sound'
  • Rising pressure forces the semi-lunar valves open
  • Blood flows through the aorta and the pulmonary artery
  • Ventricles have thick walls to provide enough contraction to provide a large amount of pressure forcing the blood out
  • the left ventricle muscle wall is especially quick as it needs to provide enough pressure to send the blood to the extremities of the body
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Valves in the control of blood

  • Blood will always move from a region of high blood pressure to low pressure
  • Sometimes, this pressure difference would cause the flow of blood to go in the wrong direction
  • Valves are open when the difference in pressure favours the required movement of blood
  • When pressure differences are reversed, the valves shut to prevent backflow
  • Made from tough, flexible, fibrous flaps
  • Cusp-shaped so change in pressure on convex/concave
  • Atrioventricular valves
    • in between the atria and ventricles
    • prevent backflow during ventricular systole
    • ensures blood flows out of the aorta and pulmonary artery
  • Semi-lunar valves
    • in the aorta and pulmonary artery
    • prevents backflow into the ventricles
    • happens when elastic walls of the vessels recoil increasing the pressure
  • Pocket valves
    • throughout the venous system
    • ensures that when veins are squeezed, blood flows back towards the heart
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Pressure and volume changes of the heart

  • Mammals have a closed circulatory system
  • This allows volumes and pressures to be maintained and regulated throughout
  • Cardiac output = Heart rate X Stroke volume
  • Measured in dm3min-1
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Structure of blood vessels

  • Tough, fibrous outer layer - resists changes to pressure from inside and outside
  • Muscle layer - can contract to control the flow of blood
  • Elastic layer - maintains blood pressure by stretching and recoiling
  • Endothelium - smooth to reduce friction and thin to llow diffusion
  • Lumen - central cavity of the blood vessel
  • Arterioles are similar to arteries but have smaller diameters but larger muscle layer and lumen
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Artery structure and function

  • Thick muscle layer compared to veins
    • smaller arteries can be constricted and dilated
    • controls the volume of blood passing through
  • Thick elastic layer compared to veins
    • important that blood pressure remains high to reach the extremities
    • stretched during systole
    • springs back during diastole
    • maintains smooth pressure surges created by the heart
  • Overall thickness of the wall is large
    • prevents arteries from bursting under high pressure
  • No valves (other than aorta and pulmonary artery)
    • doesn't tend to flow backwards due to high pressure cuased b the heart
    • threfore they do not need valves
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Arteriole structure and function

  • Arterioles carry blood under lower pressure than arteries
  • Transfer blood from arteries to capillaries
  • Thick muscle layer compared to arteries
    • contraction allows constriction of the lumen
    • this restricts blood flow
    • controls the blood supply to capillaries and tissues
  • Thin elastic layer compared to arteries
    • due to the lower blood pressure
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Vein structure and function

  • Thin muscle layer
    • veins carry blood away from tissues
    • contriction and dilation wouldn't affect the flow of blood to tissues
  • Thin elastic layer
    • low blood pressure doesn't cause them to burst
    • pressure is too low to create a recoil action
  • Small overall thickness of wall
    • no need for a thick wall as low blood pressure prevnts the vein from bursting
    • allows them to be flattened easily aiding the flow of blood
  • Has valves
    • to prevent the backflow of blood
    • low pressure increases the likelihood of backflow
    • when muscles contract, veins are compressed pressurising the blood inside
    • thie valves ensure that the direction of blood flow is only in the right direction
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Capillary structure and function

  • Function is to exchange metabolic materials such as oxygen, carbon dioxide and glucose between the cells and the circulatory system
  • Slow flow of blood
  • Walls consist mostly of lining layer (endothelium)
    • extremely thin overall
    • short diffusion distance
    • allows for rapid diffusion
  • Numerous and highly branched
    • provides a large surface area for diffusion
  • Narrow diameter
    • they can permeate into tissues so cells are never far away from a capillary
    • short diffusion pathway
  • Narrow lumen
    • squeezes red blood cells flat against the side of the capillary
    • brings red blood cells closer to the cells requiring oxygen
    • reduces diffusion distance
  • Spaces inbetween endothelial cells
    • allows white blood cells to escape and deal with infections
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Tissue fluid

  • Watery liquid
  • Contains glucose, amino acids, fatty acids, ions and oxygen
  • Supplies substances to the tissues
  • Recieves carbon dioxide and other waste material such as urea
  • It is the immediate environment of the cells
  • Formed by blood plasma
  • Tissue fluid is mostly a constant environment for the cells
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Formation of tissue fluid

  • When the blood passes into the capillaries, hydrostatic pressure is high on the arteriole side
  • Hydrostatic pressure is created by the pumping of the heart
  • This hydrostatic pressure causes tissue fluid to move out of the blood plasma
  • The outward pressure is opposed by:
    • hydrostatic pressure of the tissue fluid outside the capillaries
    • the lower water potential of the blood due to plasma proteins that causes water to move back into the blood within the capillaries
  • Overall, pressure pushes tissue fluid out of the capillaries at the arterial end
  • Pressure only pushes small molcules out of the capillaries leaving cells and proteins in the blood as they are too large to pass through the membrane
  • This is called ultrafiltration
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Return of tissue fluid to the circulatory system

  • Once tissue fluid has exchanged metabolic materials with the cells, it needs to be returned to the circulatory system
  • Most tissue fluid returns to the blood plasma back through the capillaries
    • loss of tissue fluid from the capillaries reduces the hydrostatic pressure within them
    • by the time the blood has reached the venour end of the capillary, the hydrostatic pressure is lower inside, than outside of the capillary
    • therefore, tissue fluid is returned back into the capillary due to the hydrostaic pressure difference
    • plasma has lost water and still contains protein so the lowered water potential causes water to diffuse back in via osmoss
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Lymphatic system

  • The remainder of tissue fluid is returned to the circulatory system via the lymphatic system
  • These vessels begin in the tissues and initially resemble capillaries
  • Gradually merge into larger vessels that form a network
  • larger vessels drain their contents back into the blood stream via two ducts that join the veins close to the vena cava
  • Contents in the lymphatic ststem are moved by hydrostatic pressure of the tissue fluid that left the capillaries and the contractuon of body muscles which creates pressure
  • The lymphatic systems have valves to prevent the backflow
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