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m Relation of heart rate on the duration of the cardiac cycle Tags: Visual edit Mobile edit Mobile web edit |
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{{Infobox body process
|name = Cardiac cycle
|image =
|caption =
|organisms = [[Animalia]]
|biological system = [[Circulatory system]]
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{{listen|filename=Emily's heartbeat.wav|title=A heartbeat|description=Auscultation of a healthy 16-year-old girl's heartbeat|format=[[wav]]}}
The '''cardiac cycle''' is the performance of the [[heart|human heart]] from the beginning of one heartbeat to the beginning of the next.<ref name=pollock/> It consists of two periods: one during which the heart muscle relaxes and refills with blood, called [[diastole]], following a period of robust contraction and pumping of blood, called [[systole]].<ref name=pollock/> After emptying, the heart relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems.
Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 second to complete the cycle.<ref name="wiggers">{{cite journal |last1=Silverthorn |first1=DU |title=Constructing the Wiggers diagram using core concepts: a classroom activity |journal=Advances in Physiology Education |date=10 November 2022 |volume=46 |issue=4 |doi=10.1152/advan.00046.2022 |url=https://journals.physiology.org/doi/full/10.1152/advan.00046.2022}}</ref><ref>{{cite book|last1=Gersh|first1=Bernard J|title=Mayo Clinic Heart Book|date=2000|publisher=William Morrow|location=New York|isbn=0-688-17642-9|pages=[https://archive.org/details/mayoclinicheartb00bern/page/6 6–8]|url=https://archive.org/details/mayoclinicheartb00bern/page/6}}</ref> Duration of the cardiac cycle is inversely proportional to the heart rate.<ref>{{Cite book |
==Description==
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Next is the ''isovolumic relaxation'', during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the [[Atrium (heart)|right atrium]] (from the [[vena cavae]]) and into the [[Atrium (heart)|left atrium]] (from the [[pulmonary vein]]s).<ref name=pollock/> As the ventricles begin to relax, the mitral and tricuspid valves open again, and the completed cycle returns to ventricular diastole and a new "Start" of the cardiac cycle.<ref name=pollock/><ref name=wiggers/>
Throughout the cardiac cycle, [[blood pressure]] increases and decreases. The movements of [[cardiac muscle]] are coordinated by a series of electrical impulses produced by specialized [[cardiac pacemaker|pacemaker cells]] found within the [[sinoatrial node]] and the [[atrioventricular node]]. Cardiac muscle is composed of [[
In an [[electrocardiogram]], electrical systole initiates the atrial systole at the P wave deflection of a steady signal; and it starts contractions (systole).<ref name=wiggers/>
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===Physiology===
[[File:Cardiac-Cycle-Animated.gif|thumb|[[
The [[heart]] is a four-chambered [[organ (anatomy)|organ]] consisting of right and left halves, called the [[right heart]] and the [[left heart]]. The upper two chambers, the left and right [[Atrium (heart)|atria]], are entry points ''into'' the heart for blood-flow returning from the [[circulatory system]], while the two lower chambers, the left and right [[Ventricle (heart)|ventricles]], perform the contractions that eject the blood ''from'' the heart to flow through the circulatory system. Circulation is split into [[pulmonary circulation]]—during which the right ventricle pumps oxygen-depleted blood to the lungs through the [[pulmonary trunk]] and arteries; or the [[systemic circulation]]—in which the left ventricle pumps/ejects newly oxygenated blood throughout the body via the [[aorta]] and all other arteries.<ref name=pollock/><ref name=wiggers/>
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{{main|Electrical conduction system of the heart}}
In a healthy heart all activities and rests during each individual cardiac cycle, or heartbeat, are initiated and orchestrated by signals of the heart's electrical conduction system, which is the "wiring" of the heart that carries electrical impulses throughout the body of [[cardiomyocyte]]s, the specialized muscle cells of the heart.<ref name=pollock/><ref name=wiggers/> These impulses ultimately stimulate heart muscle to contract and thereby to eject blood from the ventricles into the arteries and the cardiac [[circulatory system]]; and they provide a system of intricately timed and persistent signaling that controls the rhythmic beating of the heart muscle cells, especially the complex impulse-generation and muscle contractions in the atrial chambers.
The rhythmic sequence (or [[sinus rhythm]]) of this signaling across the heart is coordinated by two groups of specialized cells, the [[sinoatrial]] (SA) node, which is situated in the upper wall of the right atrium, and the [[atrioventricular node|atrioventricular]] (AV) node located in the lower wall of the [[right heart]] between the atrium and ventricle.<ref name=pollock/><ref name=wiggers/> The sinoatrial node, often known as the ''[[cardiac pacemaker]]'', is the point of origin for producing a wave of electrical impulses that stimulates atrial contraction by creating an [[action potential]] across myocardium cells.<ref>{{cite book|last1=Gersh|first1=Bernard J|title=Mayo Clinic Heart Book|date=2000|publisher=William Morrow|location=New York|isbn=0-688-17642-9|page=A12|url=https://archive.org/details/mayoclinicheartb00bern}}</ref><ref name="auto">{{cite book|last1=Bellenir|first1=Karen|title=Heart Diseases and Disorders Sourcebook, 2nd ed.|date=2000|publisher=Frederick G. Ruffner, Jr./Omnigraphics|location=Detroit|isbn=0-7808-0238-1|pages=[https://archive.org/details/heartdiseasesdis0000unse/page/65 65–67]|url=https://archive.org/details/heartdiseasesdis0000unse/page/65}}</ref>
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