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Cardiac cycle
Series of events form one heart beat to the next
Ensure blood flows in co-ordinated manner from pulmonary veins & superior/inferoir vena cava into atria, ventricles and out into aorta & pulmonary arteries.
Two contractions to assist blood flow
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Contraction 1:
Atrial contraction
R & L atria contract to force blood into ventricles
Each contraction is systematically-contract/relaxe
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Process of blood entering and leaving the heart
- >deoxygenated blood enters R atrium via inferior/superior vena cava
- >passes through tricuspid valve into R ventricle
- >Heart contracts to push deoxygenated blood through pulmonary valve and pulmonary arteries
- >Deoxygenated blood diffuses through lungs to get oxygen via alveoli
- >Blood enters L atrium
- >Passes through mitral valve & into left ventricle
- >Heart contracts causing aortic valve to open to allow oxygenated blood to flow throughtout the body via aorta
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Contraction 2:
Ventricle contraction
R & L ventricles contract to force blood into the vessels
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Atrial systoles (Mid-late diastole) (1)
- >Heart is relaxed/ pressure low
- >Ventricles have approx 100ml of blood in chamber
- >Blood passively flow into atria
- >Av valves open
- >Blood flow into ventricles
- >semi lunar valves are closed
- >complete emptying of atria occurs
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Ventricular systole (2)
- >Atria are in diastole
- >Ventricles begin to contract,pressure increases
- >Av valves are forced shut
- >Semilunar valves are force open
- >Blood forced from ventricles into pulmonary arteries and aorta
- >at the same time relaxed atria are receiving blood from pulmonary veins and vena cava
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Complete diastole (Early diastole) (3)
- >ventricles pressure drops
- >Ventricles are relaxed
- >Semilunar valves close
- >Blood begins to move from atria and cycle begins again
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Preload
Maximum amount of blood received by ventricles just prior to contraction
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Afterload
The amount of pressure needed by the ventricles as they contract to ensure semilunar valves are open and blood is forced out of the ventricles into the vessels.
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when can preload/afterload be altered?
During exercise, change in heart beats and pulse
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Contractility
Amount of force that produced by the heart during contraction
>to ensure blood is forced out of ventricles into pulmonary arteries and aorta
> ensure av valves are closed to prevent backflow
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Intrinsic/ cardiac Conduction
- > group of specialised myocardial cells responsible for action potential that cause heart rate.
- >Begins when cells are depolarised ( + charge) as Na infuse into cell
- >membrane permeability changes to allow movement to K ions across membrane
- >Ends at repolarisation and ions balance is restored.
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Action potential
- >Begins when cells are depolarised resulting in positive electricle charges within the cell.
- >This occurs as Na ions infuse into the cell causing action potential to fire.
- >The change in membrane permability change again and K ions move across the membrane causing repolarisation and ion balance is restored.
- >Gap junctions ensure the movement of action potentials is in one co-ordinated direction.
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Action potential (AP) pathway
- SA Node
- > SA node fires an AP causing wave of electrical currents throughout atria stimulating systole.
- AV Node > electrical currents travels to AV node
- >to complete systole,signal is paused at Avnode
- AV bundle>signal travels to AV bundle carrying it to interventricular septum
- Bundle branches
- >AV bundle divides into R&L bundle
- branches into pukinji fibres
- Purkinji Fibres
- >carry it into apex of ventricle to conducting cell of the ventricles
- >Ventricles contracts to forced blood out of vessels.
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ECG
Electrical record of heart beat
represent action potential and sys/dia throughtout heart
P Wave - beginning of Atrial action potential/ depolarisation
QRS wave - Depolarisation of ventricles when ventricle contract to push blood out of ventricles and atria relax
T wave- Ventricular repolarisation- end of action potential
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Cardia output
Amount of blood forced out of L ventricle into aorta over a minute resulting in heart rate
Heart pumps 5-6000ml blood per min, 70ml per beat
Dependent upon stretch of cardiac muscle cells as ventricles fills blood
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Hear rate
HR shows how efficient blood is flowing thru artery
It measures expansion
HR maintain via action potential/ electrical impulse
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What influence HR?
- Higher in foetus, decrease throughtout life
- Gender
- disease
- medications
- Temperature- fever
- exercise
- hormones
- electrolytes- na,ca, k
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Nervous system & HR
- Sympathetic nervous system
- Stimulates the SA & AV nodes to speed up HR
- Parasympathetic nervous system
- Slows HR until it returns to normal
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Peripheral resistance
Amount of restriction that blood may encounter as it flows around the body
Restriction is caused by change in vessel diameter (constriction or dilation) or viscosity
Temperature mau constrict or dilate vessels
Nicotine cause vasoconstriction
Alcohol & histamine cause vasodilation
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BP
The measurement of pressure exerted by the blood as it is being pushed throught arteries against inner vessel walls
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Sympathetic nervous system and BP
Uses nerves to influence BP by causing vasoconstriction of vessels
- ie laying down - BP drops
- n arteries send messages to brain causing vasoconstriction. The blood in the peripheries is pused back into systemic circulation and back towards the heart.
- BP returns to normal
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Kidneys and BP regulation
Blood volume increases = increase in CO = increase in BP= kidney increase urine output
Blood volume drops= decrease CO= BP drops = kidneys decrease urine output
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