Term
| what does electrical activity precede in the heart? |
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Definition
| mechanical activity -> which causes blood flow |
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Term
| how does pascal's law of pressure inform the movement of blood in the body? |
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Definition
| PV=nRT, if volume goes up, pressure goes down and higher pressure to lower pressure pushes blood through |
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Term
| what are important distinguishing factors of myocytes? distinguishing behavior? |
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Definition
| myocytes intercalated discs, central nuclei that can form a meshwork/electrical syncytium where one cell activates another distally through gap junctions |
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Term
| what does it mean to say tha cardiac muscle has inherent automaticity? can this be manipulated? |
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Definition
| the heart will continue to beat at 105 bpm if taken out of the body and placed in solution. these electrical impulses can be manipulated by changing ionic fluxes in the body (which both drugs and disease can do), leading to cardiac dysrhythmias/arhythmias |
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Term
| what does it mean to say that cardiac tissue has inherent excitability? |
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Definition
| the myocytes electrically activate each other, which also means if you put an electrode on a heart, you can make it go faster or slower (pacemaker) |
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Term
| what does it mean to say that cardiac tissue has inherent conductivity? |
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Definition
| one cell can affect another via intercalated discs, gap junctions and impulses can go from point A -> B |
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Term
| what does it mean to say that cardiac tissue has inherent contractility? |
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Definition
| biochemically, the heart recieves signals and is able to contract (1/3 systole, 2/3 diastole; again, electrical events produce mechanical events) |
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Term
| what does the heart have inherently? |
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Definition
| automaticity, excitability, conductivity, contractility |
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Term
| do different regions of the heart respond differently to electrical stimulus? |
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Definition
| yes; for example, the SA node, AV node, conduction fibers, and myocytes respond differently and therefore have different looking APs -> all of which compile to produce the EKG |
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Term
| what is normal heart rate? bradycardia? tachycardia? |
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Definition
normal: 60-90 bpm
bradycardia: <60 bpm
tachycardia: >100 bpm |
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Term
| what happens if you block blood flow in a coronary artery with a thrombus? how is this treated? |
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Definition
| that region of the myocardium can become ischemic and may lead to a MI, which will give an abberant EKG. (the vessel diameter will get smaller (resistance goes up), oxygen and blood flow will be lacking and APs will change). clot busters like streptokinase, t-PA, cath-labs, stents, balloons, or bypasses can all treat this condition |
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Term
| what is phase 0 of the cardiac AP? |
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Definition
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Term
| what is phase 1 of the cardiac AP? |
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Definition
|
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Term
| what is phase 2 of the cardiac AP? |
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Definition
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Term
| what is phase 3 of the cardiac AP? |
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Definition
| repolarization (or downstroke) |
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Term
| what is phase 4 of the cardiac AP? |
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Definition
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Term
| what happens during phase 0-1 of the cardiac cycle? |
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Definition
| sodium channels are activated. |
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Term
| what happens during phase 2 of the cardiac cycle? |
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Definition
| there is an influx of Ca++ which enters the myocytes -> turns an electrical event into a mechanical event |
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Term
| what happens during phase 3 of the cardiac cycle? |
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Definition
| K conductance increases even more, and Na permeability dwindles. the Ca++ channels are beginning to close and eventually the cell repolarizes back to resting state |
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Term
| what happens during phase 4 of the cardiac cycle? |
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Definition
| at rest, Na wants to get in/K wants to get out; but they are kept where they are due to the fact that non-stimulated cells are impermeable. proteins on the inside of the cell are anionic (7.4 intracellular pH), and this keeps the K+ where it is. the Na+ wants to come in b/c of the high extracellular Na+ conc. |
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Term
| what is the progression of ion conductance in a cell through a cardiac AP? |
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Definition
| first, a steep drop in K that slowly goes back up, this is quickly followed by a rapid influx of Na+ followed by a short drop-off, a slower and delayed influx of Ca++ which dies off around the same time that the K+ level is regained |
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Term
| what would happen if Na conductance was slowed? |
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Definition
| phase 0 would be longer and less steep |
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Term
| what would happen if there was an increase in K+ permeability? |
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Definition
| Na would have a problem depolarizing |
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Term
| what would happen if K channel permeability was enhanced? |
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Definition
| the cell could repolarize more quickly |
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Term
| why would a large dose of potassium kill someone? what kinds of things can cause an electrolyte imbalance? |
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Definition
| all the injected K+ would keep the intracellular K+ from wanting to leave the cell. dysfunctioning kidneys that don't excrete enough K+ can cause this, as well as medications that cause you to lose K+, and diarrhea/vomiting |
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Term
| what 2 things happen when calcium enters cells in phase 2? |
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Definition
| when Ca++ enters in the presence of ATP, it binds to sites allowing actin and myosin to interact. Ca++ also causes more Ca++ to be released from the sarcoplasmic reticulum/cell membrane |
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Term
| what do drugs like epinephrine/atropine do? |
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Definition
| these remove vagal(CN-10) effects on the heart |
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Term
| what do ionotropes do? when might they be useful? |
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Definition
| positive/negative ionotropes cause heart contraction to be more/less effective, which in the case of a pt treated with epinephrine to change heart rate, can help each contraction to be more efficient |
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Term
| what will the sum of the cardiac action potentials lead to? |
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Definition
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Term
| what is important in placement of EKG leads? |
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Definition
| they need to be placed in the same place/way each time |
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Term
| what is the EKG wave progression? |
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Definition
| P (little wave up) Q (little bit down) R (up a lot) S (little bit down) T (little wave up) |
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Term
| what is a signal toward the heart? |
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Definition
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Term
| what is a signal away from the heart? |
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Definition
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Term
| what is einthoven's triangle? |
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Definition
| lead I: red across to the left, lead II: blue from the right down, and lead III: green from the left down |
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