出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/09/04 04:49:03」(JST)
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The 'Cardiac Cycle,' Is defined as the serial wise changes which occur in the heart in a beat. Its Time Duration is 0.8 sec. It has Following Stages:-
1) Atrial Diastole(0.7 sec):- In this atria recieve blood from pulmonary vein & VenaCava.
2) Ventricular Diastole(0.5 sec) :- In this ventricle relax so pressure in ventricle decline so tricuspid, bicuspid valve open & Semilunar valve close, due to this 70-75% Blood passively flow from atria into ventricle.
3) Atrial Systole(0.1 sec) :- In this SA Node Generate action potential so both atria contract simultaneously. Due to this 25-30% Blood Pumped into ventricle.
4) Ventricular Systole(0.3 sec) :- In this AV node generate action potential so both ventricles contract and blood is pumped into aorta. In This Atrio-ventricular Valve Close & Semilunar valve open.
The State Of Heart in which all the chambers are relaxed called joint diastole. Its time is 0.4 sec. Int his Atria & Ventricle both recieve blood. In this Atrio-Ventricular Valve Open & Semilunar Valve close
In A Cardiac Cycle, Joint Systol Absent As SA node & AV Node Can not function At the same time.
Ventricles fill up with blood in 3 steps:
1} Rapid Flow: (70% blood passively)
2} Diastesis: (5% blood slowely)
3} Atrial Systolr: (25% blood Actively) (0.1 sec)
Rapid flow + Diastesis = Joint Diastole ( 0.4 sec)
Maximum Amount Of blood is transfered from auricle to ventricle in auricular daistole stage.
The heart is a four-chambered organ consisting of right and left halves. Two of the chambers, the left and right atria, are entry-points into the heart, while the other two chambers, the left and right ventricles, are responsible for contractions that send the blood through the circulation. The circulation is split into the pulmonary and systemic circulation. The role of the right ventricle is to pump deoxygenated blood to the lungs through the pulmonary trunk and pulmonary arteries. The role of the left ventricle is to pump newly oxygenated blood to the body through the aorta.
| AV valves* | Semilunar valves† | Status of ventricles and atria | |
|---|---|---|---|
| 1. early diastole/joint diastole |
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• whole heart is relaxed
• ventricles are expanding and filling |
| 2. atrial systole |
|
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• atria contract and pump blood
• additional 10–40% filling of ventricles[1] |
| 3. isovolumic ventricular contraction |
|
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• ventricular myocytes begin to contract
• ventricle volume unchanged |
| 4. ventricular ejection |
|
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• ventricles fully contract
• pump blood to rest of body |
| 5. Isovolumic ventricular relaxation |
|
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• ventricles relax
• ventricle volume unchanged |
* AV (atrioventricular) valves:
† Semilunar valves:
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Atrial systole is the contraction of the heart muscle (myocardia) of the left and right atria. Normally, both atria contract at the same time. The term systole is synonymous with contraction (movement or shortening) of a muscle. Electrical systole is the electrical activity that stimulates the myocardium of the chambers of the heart to make them contract. This is soon followed by Mechanical systole, which is the mechanical contraction of the heart.
As the atria contract, the blood pressure in each atrium increases, forcing additional blood into the ventricles. The additional flow of blood is called atrial kick.
80% of the blood flows passively down to the ventricles, so the atria do not have to contract a great amount.[2]
Atrial kick is absent if there is loss of normal electrical conduction in the heart, such as during atrial fibrillation, atrial flutter, and complete heart block. Atrial kick is also different in character depending on the condition of the heart, such as stiff heart, which is found in patients with diastolic dysfunction.
Electrical systole of the atria begins with the onset of the P wave on the ECG. The wave of bipolarization (or depolarization) that stimulates both atria to contract at the same time is due to sinoatrial node which is located on the upper wall of the right atrium.
Ventricular systole is the contraction of the muscles (myocardia) of the left and right ventricles.
At the later part of the ejection phase, although the ventricular pressure falls below the aortic pressure, the aortic valve remains open because of the inertial energy of the ejected blood.[3]
The graph of aortic pressure throughout the cardiac cycle displays a small dip (the "incisure" or "dicrotic notch") which coincides with the aortic valve closure. The dip in the graph is immediately followed by a brief rise (the "dicrotic wave") then gradual decline. Just as the ventricles enter into diastole, the brief reversal of flow from the aorta back into the left ventricle causes the aortic valves to shut. This results in the slight increase in aortic pressure caused by the elastic recoil of the semilunar valves and aorta.[4][5][6]
The total volume of blood remaining in the ventricle just at the end of the ventricular contraction is called end-systolic volume (ESV).
The closing of the mitral and tricuspid valves (known together as the atrioventricular valves) at the beginning of ventricular systole cause the first part of the "lubb-dubb" sound made by the heart as it beats. Formally, this sound is known as the First Heart Tone, or S1. This first heart tone is created by the closure of mitral and tricuspid valve and is actually a two component sound, M1, T1.
The second part of the "lub-dubb" (the Second Heart Tone, or S2), is caused by the closure of the aortic and pulmonary valves at the end of ventricular systole. As the left ventricle empties, its pressure falls below the pressure in the aorta, and the aortic valve closes. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonary valve closes. The second heart sound is also two components, A2 and P2. The aortic valve closes earlier than the pulmonary valve and they are audibly separated from each other in the second heart sound. This "splitting" of S2 is only audible during inhalation. However, some cardiac conduction abnormalities such as left bundle branch block (LBBB) allow the P2 sound to be heard before the A2 sound during expiration. With LBBB, inhalation brings A2 and P2 closer together where they cannot be audibly distinguished.
In an electrocardiogram, electrical systole of the ventricles begins at the beginning of the QRS complex.
Cardiac Diastole is the period of time when the heart relaxes after contraction in preparation for refilling with circulating blood. Ventricular diastole is when the ventricles are relaxing, while atrial diastole is when the atria are relaxing. Together they are known as complete cardiac diastole.
During ventricular diastole, the pressure in the (left and right) ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the mitral valve opens, and the left ventricle fills with blood that was accumulating in the left atrium. The isovolumic relaxation time (IVRT) is the interval from the aortic component of the second heart sound, that is, closure of the aortic valve, to onset of filling by opening of the mitral valve.[7] Likewise, when the pressure in the right ventricle drops below that in the right atrium, the tricuspid valve opens, and the right ventricle fills with blood that was accumulating in the right atrium. During diastole the pressure within the left ventricle is lower than that in aorta, allowing blood to circulate in the heart itself via the coronary arteries.
Cardiac muscle has automaticity, which means that it is self-exciting. The muscle contractions are myogenic, or generated by the muscle cell itself. This is in contrast with skeletal muscle, which requires nervous stimuli (either conscious or reflex) for excitation. The heart's rhythmic contractions occur spontaneously, although the rate of contraction can be changed by nervous or hormonal influences. For example, the sympathetic nerve accelerates heart rate and the vagus nerve decelerates heart rate.
The rhythmic sequence of contractions is coordinated by the sinoatrial (SA) and atrioventricular (AV) nodes. The sinoatrial node, often known as the cardiac pacemaker, is located in the upper wall of the right atrium and is responsible for the wave of electrical stimulation that initiates atrial contraction by creating an action potential. Once the wave reaches the AV node, situated in the lower right atrium, it is delayed there before being conducted through the bundles of His and back up the Purkinje fibers, leading to a contraction of the ventricles. The delay at the AV node allows enough time for all of the blood in the atria to fill their respective ventricles. In the event of severe pathology, the AV node can also act as a pacemaker; this is usually not the case because their rate of spontaneous firing is considerably lower than that of the pacemaker cells in the SA node and hence is overridden.
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| リンク元 | 「収縮期」 |
| 関連記事 | 「ventricular」 |