Systole and Diastole, Range, Blood Pressure, Cardiac Cycle

Systole and Diastole: Systole and diastole are fundamental aspects of the heart's function. Diastole refers to the phase when the heart muscles relax, allowing the chambers to fill with blood. Conversely, systole is when the heart muscles contract, propelling blood out of the chambers into the arteries. The balance between diastolic and systolic pressure is essential in determining a person's blood pressure.

The heart serves as the body's primary pump, ensuring that all tissues and organs receive a steady supply of oxygen-rich blood. The rhythmic contraction and relaxation of the heart muscles drive this process. Diastole represents the relaxation phase, allowing the heart to refill with blood. In contrast, systole denotes the contraction phase, where the heart expels blood into the circulation.

NEET Biology Notes on systole and diastole are essential in comprehending blood pressure, are given below. The significance of these phases, normal blood pressure ranges, and the potential risks and complications associated with hypertension (high blood pressure) and hypotension (low blood pressure) are also provided in the article below.

Systole and Diastole Range

Systole and diastole are two essential cardiac cycle phases regulating your blood pressure. During systole, the heart contracts, exerting pressure to pump blood into the circulatory system. Diastole is the phase when the heart relaxes, allowing it to refill with blood before the next contraction.

Blood pressure readings are typically presented as two numbers, such as 120/80 mmHg. The first number represents systolic pressure, while the second represents diastolic pressure. For instance, a 120/80 mmHg reading indicates a systolic pressure of 120 mmHg and a diastolic pressure of 80 mmHg.

Maintaining a healthy blood pressure is crucial for overall health. According to the American Heart Association (AHA), a healthy blood pressure range is less than 120/80 mmHg. Here is a breakdown of the categories:

• Normal: Less than 120 systolic and 80 diastolic.
• Elevated: 120–129 systolic and less than 80 diastolic, indicating a potential risk of developing high blood pressure.
• Stage 1 hypertension: 130–139 systolic or 80–89 diastolic, suggesting the need for lifestyle changes to manage blood pressure.
• Stage 2 hypertension: At least 140 systolic or at least 90 diastolic, requiring medication and lifestyle modifications.
• Hypertensive crisis: Higher than 180 systolic and/or higher than 120 diastolic, requiring immediate medical attention.

It's important to remember that these are general guidelines, and your doctor will determine your ideal blood pressure range based on your unique health circumstances.

If you have any concerns regarding your blood pressure, consult your doctor. They can help you interpret your blood pressure readings and provide guidance on maintaining a healthy blood pressure level.

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The Cardiac Cycle

The cardiac cycle describes the series of events occurring from one heartbeat to the next. It commences with the depolarization of the SA node, followed by atrial systole (0.1 seconds), ventricular systole (0.3 seconds), and ultimately, the diastole of the complete heart (0.4 seconds). These events encompass both electrical (action potential) and mechanical (changes in volume, pressure, and sound) processes.

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Calculating the Duration of the Cardiac Cycle

The duration of a complete cardiac cycle can be determined using the formula: duration = 60/HR. For instance, if an individual has a heart rate (HR) of 72 beats per minute (bpm), the duration of their cardiac cycle would be 60/72 = 0.83 seconds. It is important to note that the duration is inversely proportional to the HR.

Fundamentals of the Cardiac Cycle

The heart primarily functions to pump blood through the body via the pulmonary and systemic circulations. Its contraction generates pressure fluctuations, facilitating the movement of blood. Blood flow occurs from areas of high pressure to those of low pressure. Although events in the left and right ventricles are similar, there are lower pressure gradients in the right side. While relaxations occur simultaneously during the diastole of the complete heart lasting for 0.4 seconds, atrial and ventricular systoles do not occur simultaneously.

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Mechanism of the Cardiac Cycle

Physiologically, the contraction of both atria precedes that of both ventricles. This sequential contraction enables the separation of the right and left heart (functionally, at least) into two distinct circuits. The cardiac cycle events can be divided into diastole and systole. Diastole indicates ventricular filling, while systole indicates ventricular ejection or contraction. Despite varying pressures, both systole and diastole occur in both the right and left heart.

Diastole commences with the closing of the aortic valve and concludes with the closing of the tricuspid or mitral valve. This period encompasses ventricular filling and relaxation, preparing for the subsequent ventricular contraction. Systole begins with the tricuspid or mitral valve's closure and ends with the aortic valve's closing. During ventricular contraction, blood is forced into the arteries as the pressure in the ventricles exceeds that of the adjacent blood vessels, allowing blood to flow out.

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Phases of the Cardiac Cycle

The cardiac cycle progresses through the following stages:

1. Atrial and Ventricular Diastole – relaxed chambers filling with blood
2. Atrial Systole – contraction of the atria, pushing remaining blood into the ventricles
3. Ventricular Systole – contraction of the ventricles, forcing blood out through the aorta and pulmonary artery

The distinct phases of the cardiac cycle are:

Stage 1 – Early joint diastole, late joint diastole

Stage 2 – Atrial systole

Stage 3 – Early ventricular systole, late ventricular systol

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Systole and Diastole Pressure

Systolic Pressure

Systolic pressure is the dynamic force exerted by the blood flow against the artery walls when the heart contracts to eject blood into the arteries (systole). This dynamic ejection causes a temporary increase in arterial pressure, known as systolic blood pressure.

In a resting individual, the normal systolic blood pressure is 120 mmHg or below.

Diastolic Pressure

Diastolic pressure, on the other hand, is the pressure exerted by the blood in the arteries when the heart is in a state of relaxation between contractions (diastole).

During diastole, the heart's ventricles briefly relax, allowing them to fill with blood in preparation for the next contraction. The blood pressure measured during this relaxation phase is called diastolic blood pressure.

In a resting individual, the normal diastolic blood pressure is 80 mmHg or below. However, this pressure can increase during periods of hypertension, even when the individual is at rest.

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