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Lecture 6 & 7- circulatory function cont'd

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Question Answer
Systole
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period during which ventricles contract
diastole
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period during which verntricles relax and fill
CO=HRXSV
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cardiac output= heart rate x stroke volume -amount of blood heart pumps each minute.
What happens to cardiac output when the heart rate increases?
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Increased heart rate results in increased cardiac output (to a point).
What happens to cardiac output when the heart rate increases?
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Increased heart rate results in increased cardiac output (to a point).
When heart rate is >200 (younger) or > 170 (older), what happens?
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At high rates, less time is spent in diastole resulting in decreased filling time which leads to decreased stroke volume and decreased cardiac output.
What determines the heart rate?
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ANS activity :balance between sympathetic and parasympathetic activity. Increased stimulation of sympathetic results in faster heart rate. Increased stimulation of parasympathetic results in slower heart rate.
What is stroke volume?
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Amount of blood pumped out with each heart beat (contraction).
What do loading conditions affect?
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Stroke volume (workload)
Explain preload.
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1. size of load that must be moved by heart muscle (determined by amount of vnous blood return to ventricles prior to contraction. 2. bigger load = increased force of contraction resulting in incrased stroke volume (within limits)"starlings' law of the heart" or "Frank Starling mechanism" 3. Maxium force of contraction occurs when muscle fibers are stretched 2.5x normal resting length. Decreased filling or overfilling beyond that result in decreased cardiac output.
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Underfilling or overfilling result in...
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decreased cardiac output.
What affect does increased arterial blood pressure have on the efficiency of the heart as a pump?
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Increased arterial blood pressure leads to increased workload which leads to decreased stroke volume and decreased cardiac output.
What two conditions affect afterload?
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1. blood pressure 2. narrowing/stenosis of aortic/pulmonic valves
Define afterload
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resistance the heart must pump against to mvoe the "load" (blood). it is the force or pressure the heart must generate to eject blood from the heart.
What occurs with inotropic influences?
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change in cardiac contractility.
What occurs with inotropic influences?
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change in cardiac contractility.
What determines the afterload?
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1. Blood pressure, which presents resistance to ejection of blood from heard. The increased pressure means the heart must work harder which decreases stroke volume and decreases cardiac output. 2. An increase in resistance also occurs from stenosis of aortic/pulmonic valves.
Define contractility.
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the force with which ventricles pump, independent of effects of preload and afterload. Factors that affect contractility are called inotropic influences.
What is the difference between positive and negative inotropes?
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Sympathetic stimulation is a positive inotrope (increases contractility). Negative inotropes include hypoxia/ischemia (interferes with generation of ATP need for muscle contraction ( decreased energry=decreased muscle contraction force). Disease effects are also negative inotropes.
What do inotropic influences do?
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Change cardiac contractility.
  
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