7 Cardiac cycle & Blood vessels
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- 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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