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Internal structure of the mammalian heart
Septum: Wall of tissue that separates the R and L sides of the heart so that deoxygenated and oxygenated blood are separate.
Tricuspid SL (pulmonic) Pulmonary
Tissues Vena cavae RA RV Lungs
valve valve artery
Pulmonary AV valve SL (aortic)
Lungs LA LV Aorta Body
vein (bicuspid) valve
The LV wall is thickest because it has to provide enough force to sufficiently pressurise blood to the
heart. The LV is thinner because it only has to pump blood a shorter distance to the lungs. The atria
have the thinnest walls because blood only has to travel to the ventricles.…read more

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Cardiac cycle
Cardiac cycle: The repeating sequence of events that make up one heart beat
Systole: Contraction
Diastole: Relaxation
Stage Atrial pressure Ventricular AV SL valves Blood flow
pressure valves
Atrial systole; High Low Open Shut atria ventricles
ventricular
diastole
Ventricular Low High Shut Open ventricles arteries
systole; atrial
diastole
Diastole Low Low Shut Shut veins atria…read more

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1o heart sound=SV closure
2oheart sound=AV closure…read more

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Electrical control of the heart
Cardiac muscle is myogenic: it can contract and relax autonomously without input from nerves
The Sino-atrial node (SAN) a small patch of myogenic muscle in the RA wall contracts and initiates a wave of depolarization.
The action potential travels across atrial walls
A band of non conducting collagen prevents direct passage to the ventricles.
The action potential must travel through the atrioventricular node (AVN). There is a 0.1s delay at the the AVN to ensure the atria have emptied.
The actions potentials travel down the Bundle of His along the septum to the apex of the ventricles.
Purkinje fibres conduct waves of depolarization to contract the vesicles from the apex.…read more

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Electrocardiogram
ECG: Trace showing the electrical activity of the heart in
a cycle. Measured by placing electrodes on the skin.
P wave = atrial depolarization
QRS complex = ventricular depolarization
T wave = ventricular repolarization
NB: The ECG reading proceeds pressure
increase because the depolarization wave
causes contraction.
Fibrillation (uncoordinated ventricles)
AV block: prolonged P-S region indicates failure
of stimulation to ventricles after atrial
contractions
Heart rate from an ECG (bpm): 60/time taken for 1 heart beat…read more

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