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Cardiovascular System (Phases of cardiac cycle (Heart is at rest, blood…
Cardiovascular System
Phases of cardiac cycle
- Heart is at rest, blood flowing into atria and AV valves are open allowing blood to passively flow through to the ventricles
- SA nodes fire and atrial systole results
- Isovolumetric contraction of ventricles occupies after ventricles depolarize. Av valves close as ventricular blood surges back against the cusps. No change in volume eventhough they are contracting
- Ventricular ejection: stroke volume passes into major vessels on top of the heart
- Isovolumetric relaxation and ventricular filling follow, complete one cardiac cycle. Pressure changes that occur coincident with these events
Diastole /daɪˈæstəliː/ is the part of the cardiac cycle during which the heart refills with blood after the emptying done during systole (contraction)
A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized (contraction in heart)
Cardiac muscle
Myocytes (cardiac muscle cells) are different from skeletal muscle fibres, as they are shorter, thicker and the branching cells have one nucleus. Each myocyte is surrounded by CT endomysium, allowing access to blood capillaries. Myocytes are joined by intercalated discs with three distinct features: plasma membranes of adjacent cells display interdigitating folds, cells joined by desmosomes and gap junctions between cells
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The cardiac conduction system controls route and timing of electrical conduction. The four chambers must contract in coordinated fashion. Failure to the cardiac conduction system to transmit signals is called a heart block
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Electrocardiogram
electrical currents in the heart can be detected by recording electrodes on the skin. The electrocardiograph amplifies these signals and produces an ECG
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QRS: marks ventricular depolarization, atrial repolarization occurs simultaneously but signal is hidden by the strong wave of depolarization seen in ventricles
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