Term
| how long is the complete cardiac cycle? |
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Definition
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Term
| what are the typical systemic and pulmonary circulation pressures? |
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Definition
RA - 2
RV - 25/0
Pulm Art - 15
Lungs - 10
Pulm Vein - 6
LA - 5
LV - 120/0
Aorta - 120/80
Arteries - 93
Capillaries - 20 |
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Term
| what drives blood flow in the circulatory system? |
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Definition
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Term
| what three factors are required for effective heart pumping? |
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Definition
| AV contraction delay, synchronous contraction of ventricular cells, no tetanus |
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Term
| how long is the absolute refractory period in the heart? |
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Definition
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Term
| what type of cells are purkinje fibers made of? |
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Definition
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Term
| what role do the SA and AV nodes, and purkinje fibers play in heart contraction? |
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Definition
SA node acts as pacemaker
AV node delays AP to ventricles
purkinje fibers relay AP to ventricles |
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Term
| what path do electrical impulses follow in the heart? |
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Definition
| SA node, atrial muscle, AV node, purkinje fibers, ventricular muscle |
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Term
| what type of channels contribute to a fast action potential? |
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Definition
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Term
| what channels are responsible for the plateau of the AP in cardiomyocytes? |
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Definition
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Term
| What channels are responsible for inducing diastole? |
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Definition
| inward rectifier K channels |
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Term
| name the different phases of the ventricular cell AP and which parts are considered systole? |
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Definition
phase 0 - depolarization
phase 1 - peak
phase 2 - plateau
phase 3 - repolarization
phase 4 - diastole |
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Term
| describe how the voltage gated K channels (inward rectifier) function during the ventricular AP. |
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Definition
| during systole they are inactivated, when the cell becomes repolarized enough during phase 3 the channels open again and are able to maintain the polarized state (diastole) |
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Term
| what phase of the ventricular AP is important for heart arrythmias and is the target of anti-arrhythmics? which channels does this correspond with? |
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Definition
| phase 3, delayed rectifier K channels |
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Term
| describe the order of ion channels during the ventricular AP. |
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Definition
| Na, T-Ca, and L-Ca channels open (influx) causing spike and plateau, delayed rectifier K channels open repolarizing cell, inward rectifier K channels then open inducing diastole |
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Term
| describe the flow of the Na/Ca channel during ventricular AP. |
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Definition
| during systole the rapid influx of Na forces Ca out (phase 0-1), then the influx of Ca forces Na out (phase 1-2) |
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Term
| when are leak channels active during the ventricular AP and what role do they play? |
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Definition
| they are constitutively expressed, to maintain the resting membrane potential |
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Term
| what actions are responsible for phase 3 of the ventricular AP? |
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Definition
| inactivation of Ca channels, delayed rectifier K channels, and finally inward rectifier K channels |
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Term
| what are the similarities/differences between delayed and inward rectifier K channels? |
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Definition
| both are voltage dependent, but delayed channels are activated by depolarization, whereas inward channels are inactivated by depolarization |
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Term
| what role do ATP gated K channels play in the ventricular AP? |
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Definition
| they are normally closed due to presence of ATP, but open during ischemia |
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Term
| what role does increasing the activity of delayed K channels play in the ventricular AP duration? |
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Definition
| it decreases the duration and increases HR |
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Term
| list the flow of ions during the different ventricular AP phases. |
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Definition
0 - influx Na
1 - eflux K
2 - influx Ca, eflux K
3 - eflux K
4 - eflux K |
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Term
| how does the tension in purkinje fibers upon excitation compare to other muscle fibers and what implications does this have? |
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Definition
| it is much smaller, it is meant for conduction not contraction |
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Term
| what plays a role in the delayed response between the AP and contraction of cardiac muscle fibers? |
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Definition
| the series elastic element |
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Term
| how does the duration of the cardiomyocyte AP prevent tetanus? |
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Definition
| it overlaps and often exceeds the contractile response preventing temporal summation |
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Term
| true or false, the cardiac muscle cell does not have a membrane potential threshold for contraction? |
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Definition
| false, it does have a threshold |
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Term
| true or false, the pacemaker cells and ventricular cells have similar depolarization curves and why? |
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Definition
| false, ventricular cells have fast depolarization whereas pacemaker cells have gradual depolarization |
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Term
| what role does depolarization play in pacemaker cardiomyocytes? |
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Definition
| the gradual depolarization prevents Na channels from producing a sharp spike |
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Term
| what channels are utilized in pacemaker depolarization/repolarization? |
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Definition
| Ca and K channels, respectively |
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Term
| what channels are not present in pacemaker cardiomyocytes? |
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Definition
inward rectifier K channels
voltage dependent Na channels |
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Term
| list the phases of the pacemaker cardiomyocyte AP and which is responsible for controlling the HR? |
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Definition
phase 1 - polarized state
phase 2 - gradual diastolic depolarization
phase 3 - threshold resulting in self induced AP |
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Term
| what three factors contribute to the rate of the pacemaker AP? |
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Definition
| magnitude of diastolic prepotential, rate of diastolic depolarization, the level of the threshold potential |
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Term
| describe the role of funny currents in the pacemker AP. |
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Definition
| they are active during diastole, allowing influx of ions and helping to contribute to gradual depolarization |
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Term
| describe the role flow of Ca during pacemaker cell depolarization and the Na/Ca exchange pump. |
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Definition
| an initial influx of Ca near edge of cell triggers the internal release of Ca as well as the Ca/Na exchange pump to take in Na and kick out Ca near the edge |
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Term
| true or false, the heart is controlled by both the sympathetic and parasympathetic nervous systems? |
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Definition
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Term
| what affect does acetylcholine/epinephrine have on HR and what part of the AP cycle is affected? |
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Definition
| they slow it down and speed it up, respectively; the diastolic depolarization phase |
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Term
| what branch of nervous system is acetylcholine/epinephrine from? |
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Definition
| vagal innervation of parasympathetic, and sympathetic innervation respectively |
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Term
| define chronotropic affect. |
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Definition
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Term
| define dromotropic affect. |
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Definition
| enhances AV node conduction |
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Term
| define spontaneous affect. |
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Definition
| enhances automatic activity |
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Term
| define ionotropic affect. |
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Definition
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Term
| phosphorylation of what channel helps to control the diastolic depolarization timeframe and what affect does it have? |
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Definition
| L type Ca channel, it causes the channels to be open longer causing a more dramatic membrane current |
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Term
| what is overdrive suppression? |
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Definition
| the difference in firing rates of the various pacemaker cells in the heart, because the SA node fire the fastest they assume control of the HR, and if the heart slows down too much the next pacemaker cells take over |
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Term
| what happens to AP duration as the HR increases, what causes this and why is it important? |
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Definition
| the duration shortens due to K channels being activated sooner; because the heart needs time to fill the ventricles, if duration didn't change heart would always be in systole |
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Term
| which region of the heart has a longer conduction pathway, the endocardium or epicardium? |
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Definition
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Term
| what three factors affect cardiomyocyte conduction? |
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Definition
| AP upstroke velocity, cell size and cytoplasmic complexity, number and complexity of gap juncitons |
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Term
| true or false, the upstroke velocity and conduction velocity is determined by inward current? |
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Definition
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Term
| true or false, the smaller the cell diameter the faster the conduction velocity? |
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Definition
| false, the larger the diameter the faster the velocity |
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Term
| true or false, cardiomyocytes are electrically isolated from each other? |
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Definition
| false, they are connected via gap junctions |
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Term
| true or false, gap junctions can close? |
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Definition
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Term
| list some potential causes for MI. |
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Definition
reduction of blood flow/lack of O2
intracellular pH and ATP decrease
opening of ATP gated K channels
membrane pump failure (K leaks out)
decrease in resting membrane potential
AP decrease
conduction velocity decrease |
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Term
| what affect does and increase in extracellular K have on cardiomyocyte AP and what can the cells do to try and prevent its affects? |
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Definition
the AP is reduced in size
the AP is delayed
the AP duration shortens
cells close gap junctions to prevent spread of depolarization |
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