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D4 - The Heart (Cardiac Cycle (Electrocardiograms (ECG) (Measure electric…
D4 - The Heart
Cardiac Cycle
One heartbeat - a series of events from the beginning of one heartbeat to the beginning of the next heartbeat
72 cardiac cycles in a minute, meaning one occurs every 0.8 second on average
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SA node and AV node
SA node - inside the right atrium that acts as a pacemaker, causing both atria to contract
AV node - inside the right atrium, causes ventricles to contract. Impulses reach 0.03 seconds after being emitted from SA node
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Narrower conducting fibres branch out from these bundles and carry impulses to all parts of walls of the ventricle
Electrocardiograms (ECG)
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P wave - SA node fires, atrial systole
QRS complex - (Q) AV node fires, ventricular systole
T wave - ventricular diastole. AV node is repolarising, getting ready for the next cardiac cycle
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Blood Pressure
Cuff placed on the upper arm --> inflated to constrict blood in the arteries from reaching the forearm --> cuff deflated and the sound of blood flow is listened with a stethoscope --> cuff is further deflated when there is no sound
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Heart Diseases
Artificial pacemakers
Medical devices surgically fitted into patients with a malfunctioning SA node or a block in signal conduction pathway
Regulates heart beat, ensures a steady rhythm
Defirbillation
Used during a heart attack/ventricular fibrillation - twitching of the ventricles to rapid, chaotic contraction of muscle cells
Defibrillator first detects whether the ventricles are fibrillating, delivers electric discharge that stops defibrillation, resets signals from the SA node and resumes normal heartbeat
Hypertension
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Develops over many years, usually due to narrowing of blood vessels from plaque
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Thrombosis
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Usually develops when blood is allowed to sit in a vessel for prolonged period of time (lack of movement)
Can travel to the brain and block a blood vessel (stroke); lungs (embolism); coronary arteries (heart attack)
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Cardiac Muscles
Intercalated disc
Joins the cytoplasm to adjoining cells, they allow movement of ions --> transmit signals better
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Myogenic
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Does not become fatigue allow continuous, long contractions, unlike skeletal muscles