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74 Cards in this Set
- Front
- Back
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What is a cardiac cycle?
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the period between the start of one heartbeat and the beginning of the next
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How do the contractions occur?
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two atria contract first pushing blood into the ventricles and then the two ventricles contract pushing blood through pulmonary and systemic circuits
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What provides the heart with normal spacing between atrial and ventricular contractions?
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pacemaking and conductng systems
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What two phases can a cardiac cycle be divided into?
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systole and diastole
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What occurs during systole?
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chamber contracts and pushes blood into adjacent chamber or trunk
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What occurs during diastole?
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chamber fills with blood and prepares for next contraction
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What happens to the cardiac cycle when the heart rate increases?
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all phasees of the cardiac cycle are shortened
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How much time is one complete cardiac cycle?
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800 msec
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What happens during atrial systole?
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the atria contract filling the relaxed ventricles with blood
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How long does ventricular systole last?
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270 msec
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What occurs during the first phase of ventricular systole?
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ventricles contract and push the AV valves closed
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What is the first phase of ventricular systole also known as?
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isovolumetric contraction
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What occurs in the second phase of ventricular systole?
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ventricular pressure rises and exceeds pressure in the arteries, semilunar valves open and blood is forced out of the ventricle
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What is another name for the second phase of ventricular systole?
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ventricular ejection
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What happens during early ventricular diastole?
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the pressure in the ventricles drop, blood flows back against the semilunar valves and forces them closed
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What happens at the period of isovolumetric relaxation?
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blood flows into the relaxed atria but the AV valves stay closed
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What happens during late ventricular diastole?
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all chambers are relaxed
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How long does ventricular diastole last?
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530 msec
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Are pressures lower in the right or left side of the heart?
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right
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What does S1 represent?
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the start of ventricular contraction, the sound is the AV valves closing
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When does S2 occur?
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when the semilunar valves close
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What is S3 associated with?
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blood flowing through the ventricles
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What is S4 associated with?
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atrial contraction
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How is the heart rate established?
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SA node
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What is the best indicator of overall blood flow?
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cardiac output
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What is cardiac output?
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the amount of blood pumped by the left ventricle in one minute
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What does cardiac output depend on?
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heart rate and stroke volume
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What is stroke volume?
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the amount of blood pumped out of the ventricle in a single heartbeat
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How do you calculate cardiac output?
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multiply heart rate by stroke volume
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How does the body adjust cardiac output?
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so that peripheral tissues receive an adequate circulatory supply in all conditions
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What is automaticity?
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the cardiac muscle tissue contracting on its own without any hormonal stimulation
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What is the network of cardiac muscle cells that are responsible for initiating and distributing the stimulus to contract?
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the conducting system
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How does each heartbeat begin?
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with an action potential created by the SA node
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Where is the SA node located?
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posterior wall of the right atrium
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How will the heart continue to beat if the SA node and internodal pathways are damaged?
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the AV node
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What distributes the contractile stimulus to atrial muscle cells?
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internodal pathways
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What are responsible for the depolarization of the ventricular myocardial cells?
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purkinje fibers
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What is the only electrical connection between the atria and the ventricles?
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AV bundle
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When does atrial contraction begin?
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50 msec after an impulse is generated at the SA node
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What is the maximum heart rate?
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230 bpm
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Why do cardiac muscle cell contractions last longer than skeletal muscle fiber contractions?
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differences in membrane permeability
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How is the action potential prolonged in a cardiac muscle cell?
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calcium ions continue to enter the cell
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Why does the refractory period continue until relaxation is well under way?
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summation cant occur and and tetanic contractions cant occur
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What are the three stages of an action potential in a cardiac muscle cell?
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rapid depolarization, plateau, repolarization
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What is the gradual depolarization that occurs after each repolarization?
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prepotential or pacemaker potential
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Where is the rate of spontanious depolarization the fastest?
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SA node
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Why does the SA node establish the heart rate?
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because it reaches threshold first
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What causes a decline in heart rate?
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acetylcholine released by parasympathetic neurons
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What causes an increase in heart rate?
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norepinephrine released by sympathetic neurons
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What is the normal range of heart rates?
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60-100 bpm
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Where are the autonomic headquarters for cardiac control located?
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medulla oblongata
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How do cardiac centers of the medulla oblongata innervate the heart?
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cardiac plexus
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What controls the parasympathetic neurons that slow the heart rate?
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cardioinhibitory center
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What controls the sympathetic neurons that increase the heart rate?
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cardioacceleratory center
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Where does sympathetic innervation arrive at the heart?
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postganglionic fibers within the cardiac nerves
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Where does parasympathetic innervation arrive at the heart?
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through the vagus nerve and synapses with gangion cells in cardiac plexus
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What do sympathetic fibers innervate?
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-nodes
-conducting system -atrial and ventricular myocardium |
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What do parasympathetic fibers innervate?
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-SA and AV node
-atrial musculature -a little ventricular musculature |
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What are activities of the cardiac centers regulated by?
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reflex pathways and input from higher centers
*mostly parasympathetic and sympathetic in the hypothalamus |
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Is the normal resting heart rate slower or faster than the intrinsic SA nodal stimulation rate?
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slower
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How is stroke volume changed?
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altering the end diastolic volume, the end systolic volume, or both
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What is the end diastolic volume influenced by?
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venous return and filling time
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What are the three major factors of venous return?
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1. blood volume
2. muscular activity 3. rate of blood flow through peripheral capillaries |
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When is venous return decreased?
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when blood volume goes down significantly
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When is venous return increased?
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-when skeletal muscles contract
-peripheral tissues increase their activities |
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Does slowing the heart rate increase or decrease the end diastolic volume?
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increase
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Does increasing the heart rate increase or decrease diastolic volume?
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decrease
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What is the relationship between end diastolic volume and preload?
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the greater the EDV, the larger the preload
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What is the amount of myocardial stretching called?
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preload
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What is the end systolic volume influenced by?
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contractility and the afterload
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What is contractility?
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the amount of force produced during a contraction at a given amount of preload
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What is afterload?
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the amount of tension the contracting ventricle must produce to force open the semilunar valve and eject blood
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If the afterload increases, what happens to the stroke volume?
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decreases
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What is afterload increased by?
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any factor that restricts blood flow through the arterial system
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