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Endocardium
Innermost layer of the heart. Lines the chambers.
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Pericardium
- Protective sac surrounding the heart
- Consists of the epicardium (touches the heart) and
- Parietal pericardium (outer layer)
- Containts 25 mL fluid between them
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Atrioventricular Valves
- Control blood flow between atria and ventricles
- Right: tricuspid
- Left: mitral
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Semilunar Valves
- Regulate blood flow from ventricles and the arteries
- Aortic: left ventricle to aorta
- Pulmonic: right ventricle to pulmonary artery
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Anastomosis
Communication between two or more vessels
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Cardiac Cycle
The period of time from the end of one cardiac contraction to the end of the next
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Diastole
The period of time when the myocardium is realxed and cardiac filling and coronary perfusion occur
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Systole
The period of the cardiac cycle when the myocardium is contracting
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Ejection Fraction
Ratio of blood pumped from the ventricle to the amount remaining at the end of diastole
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Stroke Volume
The amount of blood ejected by the heart in on cardiac contraction
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Preload
The pressure within the ventricles at the end of diastole; commonly called the end-diastolic volume
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Starling's Law of the Heart
Law of physiology stating that the more the myocardum is stretched, up to a certain amount, the more forcefull susbsequent contraction will be
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Afterload
The resistance against which the heart must pump
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Factors Effecting Strok Volume
- Preload
- Cardiac contractility
- Afterload
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Cardiac Output
The amount of blood pumped by the heart in one minute
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Chronotropy
Pertaining to heart rate
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Inotropy
Pertaining to cardiac contractile force
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Dromotropy
Pertaining to the speed of impulse transmission
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Intercalated Discs
Specialized bands of tissue inserted between myocardial cells the increase rate in which the action potential is spread from cell to cell.
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Syncytium
Group of cardiac muscle cells that physiologically function as a unit
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Cardiac Depolarization
A reversal of charges at a cell membrane so the the inside of the cell becomes positive relative to the outside; the opposite of the cell's resting state in theich the inside is negative in relation to the outside
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Resting Potential
The normal electrical state of cardiac cells
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Action Potential
The stimulation of myocardial cells, as evidenced by a charge in the membrane electrical charge, that subsequently spreads across the myocardium
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Repolarization
Return of a muscle cell to its preexcitation resting state
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Excitability
Ability of the cells to respond to an electrical stimulus
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Conductivity
Ability of the cells to propagate the electrical impulse from one cell to another
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Automaticity
Pacemaker cells' capability of self-depolarization
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Contractility
Ability of muscle cells to contract or shorten
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ECG Leads
- Bipolar (limb)
- Augmented (unipolar)
- Precordial
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Bipoar Limb Leads
EKG leads applied to the arms and legs that contain two electrodes of opposite (positive and negative) polarity (leads I, II, III)
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Einthoven's Triangle
The triangle around the heart formed by the bipolar limb leads
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Augmented Limb Leads (Unipolar)
EKG leads applied to the arms and legs, consisting of one positive electrode and a nonpolarized reference point that is created by the EKG machine combing two additional electrodes (aVR, aVL, aVF)
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Precordial (chest) Leads
EKG leads applied to the chest in a pattern that permits a view of the horizontal plane of the heart (V1, V2, V3, V4, V5, V6)
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EKG Components
- P wave
- QRS complex
- T wave
- U wave
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EKG Time Intervals
- PR Interval: 0.12-0.20 seconds (3-5 small boxes)
- QRS Segment: 0.08-0.12 seconds (2-3 small boxes)
- QT Interval: 0.33-0.42 seconds
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QT Interval
Period from the beginning of the QRS to the end of the T wave
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