SIKLUS JANTUNG

Summary

The cardiac cycle is a critical process that involves the heart's phases of contraction (systole) and relaxation (diastole). During diastole, blood fills the heart as the atria relax, while systole pumps blood into the arteries as the ventricles contract. Blood moves through the heart, with about 80% filling the ventricles passively and 20% through atrial contraction. The cycle is marked by various phases, including isovolumic phases and ejection phases, and produces key values like end-diastolic volume (120 mL) and stroke volume (70 mL). The heart's rhythmic electrical impulses coordinate these events, which enable blood circulation and oxygen transport.

Takeaways

• 😀 The cardiac cycle consists of two main phases: diastole (heart relaxation) and systole (heart contraction).
• 😀 Diastole involves the heart muscle relaxing, allowing blood to fill the atrium and ventricles.
• 😀 Systole is when the heart contracts, pumping blood from the ventricles into the arteries.
• 😀 Blood flows from the body into the heart through veins, with the higher pressure in veins pushing blood into the atrium.
• 😀 About 80% of blood flows into the ventricle during diastole, while the remaining 20% is pushed by atrial systole.
• 😀 The impulse in the SAN (Sinoatrial Node) initiates atrial depolarization, resulting in atrial systole.
• 😀 Ventricular systole, marked by QRS complex in an ECG, pumps blood into the arteries after ventricular contraction.
• 😀 The end-diastolic volume (EDV) refers to the 120 mL of blood in the ventricles before systole.
• 😀 The early phase of ventricular systole is called isovolumic contraction, where pressure builds and valves close.
• 😀 The late phase of ventricular systole is the ejection phase, where blood is pumped out into the arteries, with a stroke volume of 70 mL.
• 😀 After systole, the ventricles relax, and during ventricular diastole, blood re-enters the ventricles, restarting the cycle.

Q & A

What is the cardiac cycle, and how long does it last?

The cardiac cycle refers to the process of blood pumping and filling in the heart. It lasts about 0.8 seconds in one heartbeat.

What is diastole, and what happens during this phase?

Diastole is the phase of the cardiac cycle where the heart muscle relaxes and stretches. During this time, blood fills the atrium and ventricle, with the atrium receiving blood from the veins.

How does blood flow into the atrium during diastole?

Blood from the veins, which have higher pressure than the atrium, flows into the atrium due to the pressure difference, accounting for about 80% of the blood volume entering the ventricle.

What is atrial systole and its role in the cardiac cycle?

Atrial systole is the contraction of the atrium that occurs after atrial depolarization (P wave on ECG). It pumps the remaining 20% of blood into the ventricle.

What happens during ventricular systole?

Ventricular systole occurs when the ventricle contracts after depolarization (QRS complex on ECG). This phase has two stages: the isovolumic contraction phase and the ejection phase.

What is the significance of the first heart sound (S1)?

The first heart sound (S1) occurs during the early phase of ventricular systole when the tricuspid and mitral valves close to prevent blood from flowing back into the atrium.

What is the stroke volume, and how much is ejected during the ejection phase?

Stroke volume is the volume of blood pumped by the ventricle during one heartbeat. During the ejection phase, approximately 70 mL of blood is ejected into the arteries.

What is the end-systolic volume?

The end-systolic volume is the remaining blood in the ventricle after ventricular systole, which is around 50 mL.

How does the second heart sound (S2) occur?

The second heart sound (S2) happens during the early phase of ventricular diastole when the aortic and pulmonary valves close due to higher pressure in the arteries compared to the ventricle.

What happens during the isovolumic relaxation phase?

During the isovolumic relaxation phase, both the pulmonary and aortic valves remain closed, and the blood volume in the ventricle stays constant until the ventricle begins to relax further and blood re-enters during the final phase of ventricular diastole.