contraction Flashcards
What are the five periods of the cardiac cycle, and what happens during each phase?
The cardiac cycle is the sequence of events that occur during one complete heartbeat, including the contraction and relaxation of the heart chambers. It ensures that blood is pumped efficiently throughout the body. The cycle can be divided into several phases:
- Atrial Systole (Contraction of the Atria)
Start: The cycle begins when the atria contract to push the remaining blood into the ventricles.
Pressure Changes: Atrial pressure increases, and the AV (atrioventricular) valves are open, allowing blood to flow from the atria into the ventricles.
End: This phase contributes to about 20% of the total ventricular filling. - Ventricular Diastole (Relaxation of the Ventricles)
Start: After the atria contract, the ventricles are relaxed, and they start filling with blood from the atria.
Pressure Changes: As the ventricles relax, the pressure inside them drops, causing the AV valves to open and blood to flow passively from the atria into the ventricles.
End: The ventricles are almost completely filled at the end of this phase. - Isovolumetric Contraction
Start: The ventricles begin to contract, but the pressure inside them is not yet high enough to open the semilunar valves (pulmonary and aortic valves). The AV valves are closed to prevent blood from flowing back into the atria.
Pressure Changes: The pressure in the ventricles rises rapidly during this phase, but the volume of blood remains constant since no valves are open yet.
End: When ventricular pressure exceeds the pressure in the arteries, the semilunar valves open. - Ventricular Ejection
Start: The pressure in the ventricles exceeds the pressure in the pulmonary artery and aorta, causing the semilunar valves to open.
Pressure Changes: Blood is pumped from the ventricles into the arteries (pulmonary artery from the right ventricle and aorta from the left ventricle). Ventricular pressure rises and then starts to fall as the blood is ejected.
End: The ventricles are emptied, and the semilunar valves close as the pressure in the ventricles drops below the pressure in the arteries. - Isovolumetric Relaxation
Start: After ventricular ejection, the ventricles relax, and the semilunar valves close to prevent blood from flowing back into the ventricles.
Pressure Changes: The pressure in the ventricles falls, but the AV valves remain closed.
End: As ventricular pressure continues to fall and becomes lower than atrial pressure, the AV valves open, and the cycle begins again.
Summary of the Phases:
Atrial Systole: Atria contract to fill ventricles.
Ventricular Diastole: Ventricles relax and fill with blood.
Isovolumetric Contraction: Ventricles contract, but no blood is ejected yet.
Ventricular Ejection: Blood is pumped into the arteries.
Isovolumetric Relaxation: Ventricles relax, and semilunar valves close.
This cycle repeats continuously and is responsible for maintaining blood flow throughout the body. The entire cycle takes about 0.8 seconds in a normal heart rate of 75 beats per minute.
What are the two distinct heart sounds heard with a stethoscope, and what causes them?
When using a stethoscope, you can hear two distinct sounds during each cardiac cycle. These heart sounds are often described by the two syllables “lub” and “dup,” and the sequence is lub-dup, pause, lub-dup, pause, and so on. The first heart sound (lub) is caused by the closing of the AV valves. The second heart sound (dup) occurs when the semilunar valves close at the end of ventricular systole. The first heart sound is longer and louder than the second heart sound, which tends to be short and sharp.
What are heart murmurs, and what causes them?
Heart Murmurs: Abnormal or unusual heart sounds caused by turbulent blood flow. Normally, blood flow is silent, but when it encounters obstructions, it generates sounds that can be heard with a stethoscope.
Common Causes:
In young children and some elderly people with healthy hearts, murmurs can occur because the heart walls are relatively thin, causing them to vibrate with rushing blood.
In Adults (Not in the Young or Elderly):
Valve Problems: Most murmurs in adults indicate valve issues, such as:
Incompetent Valve: If a valve does not close tightly, blood flows back through it after it has supposed to close, creating a swishing sound.
Stenosed Valve: When a valve is narrowed, blood flows turbulently through it, creating distinct sounds.
What is cardiac output (CO), and how is it calculated?
Cardiac Output (CO): The amount of blood pumped out by each side of the heart (each ventricle) in 1 minute. It is the product of:
Heart Rate (HR): The number of heartbeats per minute.
Stroke Volume (SV): The volume of blood pumped by a ventricle with each heartbeat.
How does cardiac output (CO) vary with the body’s demands, and how are stroke volume and heart rate regulated?
The normal adult blood volume is about 6,000 ml, so nearly the entire blood supply passes through the body once each minute. Cardiac output varies with the demands of the body. It rises when the stroke volume is increased, or the heart beats faster, or both; it drops when either or both of these factors decrease.
What percentage of blood does a healthy heart pump with each heartbeat, and what factors influence stroke volume?
A healthy heart pumps out about 60 percent of the blood present in its ventricles. As noted previously, this is approximately 70 ml (about 2 ounces) with each heartbeat. Three factors influence stroke volume: preload, contractility, and afterload.
What is the Frank-Starling law of the heart, and how does preload affect stroke volume?
The Frank-Starling law of the heart is essentially about how the heart works more effectively when it fills up with the right amount of blood before it contracts.
Here’s a simpler breakdown:
Preload: This is the amount of blood that fills the heart’s ventricles before it pumps. The more blood the heart gets, the more the heart muscle stretches, and this stretching leads to a stronger contraction. Think of it like pulling a rubber band—if you stretch it more, it snaps back stronger.
Factors that affect preload:
Venous return: This is how much blood is returning to the heart. The more blood that comes back, the more the heart stretches and the stronger the contraction.
Heart rate: If the heart beats slowly, it gives the ventricles more time to fill with blood. If it beats quickly, there’s less time to fill, which can affect how much the heart stretches.
Muscular pump: When you exercise, your muscles help push blood back to the heart through the veins. This is like a pump that increases the amount of blood returning to the heart, which helps it contract more powerfully.
What happens with low venous return: If there’s less blood coming back to the heart (like in cases of blood loss or a very fast heartbeat), the heart can’t stretch as much, and the stroke volume (amount of blood pumped) decreases.
In short, when the heart fills with more blood, it can contract more forcefully and pump more blood. Factors like venous return and heart rate influence how much blood the heart gets, and how well it pumps.
