Cardiac cycle

Definition

The cardiac cycle is the series of events that occur in the heart during one complete heartbeat, including the contraction and relaxation of the heart muscles. This cycle consists of two main phases: systole, where the heart contracts to pump blood out, and diastole, where the heart relaxes and fills with blood. Understanding the cardiac cycle is essential for grasping how the heart functions to maintain blood circulation throughout the body.

5 Must Know Facts For Your Next Test

1. The entire cardiac cycle lasts about 0.8 seconds at a normal resting heart rate of around 75 beats per minute.
2. During systole, the ventricles contract with higher pressure than during diastole, which is crucial for effective blood ejection into the aorta and pulmonary artery.
3. The atrioventricular (AV) valves close at the beginning of systole, producing the 'lub' sound of the heartbeat, while closure of the semilunar valves at the end of systole creates the 'dub' sound.
4. The cardiac cycle is influenced by various factors including neural and hormonal signals that can increase or decrease heart rate and contractility.
5. An efficient cardiac cycle ensures adequate perfusion of organs and tissues, adjusting according to physiological needs during activities like exercise or rest.

Review Questions

• How do systole and diastole differ in terms of their role in the cardiac cycle?
  • Systole and diastole are two critical phases of the cardiac cycle that serve distinct roles. Systole involves the contraction of heart muscles, specifically pushing blood out from the ventricles into the arteries, which is essential for circulation. In contrast, diastole is when the heart relaxes, allowing the chambers to fill with blood from the atria. Both phases are necessary for maintaining effective blood flow and ensuring that all areas of the body receive oxygenated blood.
• Discuss how changes in heart rate can affect the duration of the cardiac cycle and overall cardiovascular function.
  • Changes in heart rate directly influence the duration of both systole and diastole, thereby altering the overall length of the cardiac cycle. For instance, an increased heart rate shortens both phases but particularly decreases diastolic filling time, which can lead to reduced stroke volume if there isn’t enough time for adequate ventricular filling. Conversely, a slower heart rate allows more time for filling during diastole, potentially improving stroke volume. These adjustments are crucial for ensuring that oxygen delivery meets metabolic demands during various activities.
• Evaluate how understanding the cardiac cycle can aid in diagnosing cardiovascular diseases.
  • Understanding the cardiac cycle is fundamental for diagnosing cardiovascular diseases as it helps clinicians interpret abnormal heart sounds, assess valve function, and evaluate cardiac output. For example, abnormalities in systolic or diastolic function can indicate conditions such as hypertension or heart failure. Additionally, monitoring changes in heart rate during different phases of the cardiac cycle can provide insights into arrhythmias or other electrical conduction issues. Thus, a comprehensive grasp of these processes enables healthcare professionals to identify issues early and implement appropriate interventions.

Related terms

Systole: The phase of the cardiac cycle where the heart muscles contract, pumping blood from the chambers into the arteries.

Diastole:

The phase of the cardiac cycle in which the heart muscles relax, allowing the chambers to fill with blood.

Heart Rate: The number of times the heart beats per minute, which is influenced by the duration of the cardiac cycle.