The heart and Cardiac Cycle

Questions and Answers

What is the main purpose of diastole in the cardiac cycle?

To contract the heart chambers

To eject blood from the heart

To close the valves

To fill the heart chambers with blood (correct)

The entire heart undergoes systole during the cardiac cycle.

False

What characterizes ventricular systole?

Ventricles contract to eject blood out of the heart.

The __________ valves prevent backflow from the ventricles to the atria during ventricular systole.

atrioventricular Signup and view all the answers

Match the phase of the cardiac cycle with its description:

Atrial Systole = Atria contract to fill ventricles Ventricular Systole = Ventricles contract to eject blood Diastole = Heart relaxes to refill chambers Atrial Diastole = Atria fill with blood during ventricular systole Signup and view all the answers

Which statement correctly describes the role of aortic pressure in the cardiac cycle?

It reflects blood pressure in the aorta essential for outflow Signup and view all the answers

Atrioventricular valves close when ventricular pressure exceeds atrial pressure.

True Signup and view all the answers

How long does one complete cycle of the cardiac cycle approximately last?

0.7 to 0.8 seconds Signup and view all the answers

What is the role of the sinoatrial (SA) node in the heart?

To initiate electrical impulses and trigger atrial contraction Signup and view all the answers

The atrioventricular (AV) node allows the atria and ventricles to contract simultaneously.

False Signup and view all the answers

What is the function of the Purkinje fibers in the heart?

To distribute electrical impulses throughout the ventricles Signup and view all the answers

The _____ is known as the natural pacemaker of the heart.

sinoatrial node Signup and view all the answers

Match the following components of the heartbeat control mechanism with their functions:

SA Node = Initiates heartbeat AV Node = Delays electrical signals Bundle of His = Transmits impulses to the apex Purkinje Fibers = Stimulates ventricular contraction Signup and view all the answers

What ensures that blood is effectively pushed out from the bottom of the heart?

The Bundle of His Signup and view all the answers

Cardiac muscles are capable of generating their own electrical impulses.

True Signup and view all the answers

What prevents the ventricles from contracting until the electrical signal reaches the apex?

The insulating layer around the Bundle of His Signup and view all the answers

Which chamber of the heart receives deoxygenated blood?

Right Atrium Signup and view all the answers

The left ventricle has a thinner wall compared to the right ventricle.

False Signup and view all the answers

What is the role of the pulmonary artery?

It delivers deoxygenated blood from the heart to the lungs for oxygenation. Signup and view all the answers

The left atrium receives oxygenated blood from the __________.

lungs Signup and view all the answers

Match the heart valves with their locations:

Tricuspid Valve = Between right atrium and right ventricle Bicuspid Valve = Between left atrium and left ventricle Semilunar Valves = At the exit of right ventricle Atrioventricular Valves = Between atria and ventricles Signup and view all the answers

Which blood vessel is the largest in the body?

Aorta Signup and view all the answers

Veins are typically responsible for carrying oxygenated blood.

False Signup and view all the answers

What is the function of the septum in the heart?

It separates the left and right sides of the heart. Signup and view all the answers

What is the primary function of coronary arteries?

To supply oxygenated blood to the cardiac muscle Signup and view all the answers

The right ventricle has a thicker wall than the left ventricle.

False Signup and view all the answers

What do the semilunar valves prevent?

Backflow of blood from the arteries into the ventricles. Signup and view all the answers

The ____ valves are responsible for controlling blood flow between the atria and ventricles.

atrioventricular Signup and view all the answers

Match the following heart chambers with their characteristics:

Left Atrium = Receives oxygenated blood from the pulmonary veins Right Atrium = Receives deoxygenated blood from the body Left Ventricle = Pumps oxygenated blood to the body Right Ventricle = Pumps deoxygenated blood to the lungs Signup and view all the answers

What happens if there is a blockage in the coronary arteries?

Myocardial infarction (heart attack) can occur Signup and view all the answers

Atria are the lower chambers of the heart.

False Signup and view all the answers

What major blood vessel carries oxygenated blood from the left ventricle to the body?

Aorta Signup and view all the answers

The heart does not fatigue as long as oxygen and glucose are provided, allowing for __________ function.

continuous Signup and view all the answers

Which chamber contains thinner muscular walls?

Right ventricle Signup and view all the answers

What is the formula for calculating cardiac output?

Cardiac Output = Heart Rate x Stroke Volume Signup and view all the answers

Atrial systole occurs when the ventricles are contracting.

False Signup and view all the answers

What happens to the volume and pressure in the ventricles during ventricular systole?

Volume decreases and pressure increases. Signup and view all the answers

The __________ valves open when ventricular pressure rises above arterial pressure.

semilunar Signup and view all the answers

Match the phases of the cardiac cycle with their effects on the heart:

Diastole = Atria and ventricles relax, filling with blood Atrial Systole = Atria contract, pushing blood into ventricles Ventricular Systole = Ventricles contract, ejecting blood into arteries Signup and view all the answers

Which valves prevent backflow into the ventricles after blood has been ejected?

Semilunar valves Signup and view all the answers

A higher heart rate automatically leads to increased stroke volume.

False Signup and view all the answers

What occurs during diastole?

The heart chambers relax and fill with blood. Signup and view all the answers

The __________ valves are located between the atria and ventricles.

atrioventricular Signup and view all the answers

What is the primary function of the semilunar valves during the cardiac cycle?

To open when pressure in the ventricles exceeds pressure in the arteries Signup and view all the answers

Study Notes

Cardiac Cycle Overview

Cardiac cycle consists of diastole (relaxation) and systole (contraction) phases.
Diastole allows the heart chambers to fill with blood, while systole pushes blood out.

Diastole and Systole

Diastole is characterized by relaxation of the entire heart.
Systole can refer to atrial systole (atria contract) or ventricular systole (ventricles contract).
A situation where the whole heart undergoes systole does not occur; blood flow would cease.

Pressure Dynamics in the Cardiac Cycle

Atrial pressure (in blue) represents blood pressure within both the left and right atria.
Ventricular pressure (in green) is higher due to thicker ventricular walls allowing stronger contractions.
Aortic pressure (in red) reflects blood pressure in the aorta and is essential for understanding outflow.

Phases of the Cardiac Cycle

Cycle duration is approximately 0.7 to 0.8 seconds.
Major phases include:
- Atrial Systole: Atria contract forcing blood into ventricles; occurring during ventricular diastole.
- Ventricular Systole: Ventricles contract increasing pressure to eject blood out of the heart; occurring during atrial diastole.
- Diastole: The entire heart relaxes, allowing chambers to refill with blood.

Intersection Points in Graph

Understanding pressure relations at intersection points:
- When ventricular pressure exceeds atrial pressure, atrioventricular (AV) valves close to prevent backflow.
- As ventricular pressure rises further, it surpasses aortic pressure, causing semilunar valves to open for blood ejection.

Valve Functionality

Atrioventricular valves (bicuspid and tricuspid) prevent backflow from ventricles to atria during ventricular systole.
Semilunar valves open when ventricular pressure is higher than aortic pressure, allowing blood to flow into the arteries.
Semilunar valves close when ventricular pressure drops below aortic pressure, preventing backflow.

Final Notes on Blood Flow

The cycle is a continuous process with blood returning to the atria during diastole.
Atrial contraction facilitates the final blood push into the ventricles.
The heart sounds (thump-thump) attributed to the closing of valves during the cardiac cycle serve as an indicator of heart activity.

Summary of Heart Sounds

First heart sound corresponds to atrioventricular valves closing.
Second heart sound is due to semilunar valves closing.
Heart rate typically averages around 70 beats per minute.

Cardiac Cycle Overview

The cardiac cycle includes two main phases: diastole (relaxation) and systole (contraction).
Diastole enables heart chambers to fill with blood, while systole is responsible for ejecting blood from the heart.

Diastole and Systole

Diastole involves complete relaxation of the heart.
Systole can be subdivided into atrial systole (contraction of atria) and ventricular systole (contraction of ventricles).
Systolic state of the entire heart is impractical as it would halt blood flow.

Pressure Dynamics in the Cardiac Cycle

Atrial pressure indicates blood pressure in the left and right atria.
Ventricular pressure is higher due to the muscular strength of the ventricular walls, facilitating effective contractions.
Aortic pressure is critical for understanding the pressure dynamics of blood outflow from the heart.

Phases of the Cardiac Cycle

The cardiac cycle lasts about 0.7 to 0.8 seconds.
Atrial Systole: Atria contract to push blood into the ventricles during ventricular diastole.
Ventricular Systole: Ventricles contract, raising pressure to expel blood while atria are relaxed.
Diastole: The heart relaxes, promoting refilling of the chambers with blood.

Intersection Points in Graph

AV valves close when ventricular pressure exceeds atrial pressure, preventing backflow.
When ventricular pressure exceeds aortic pressure, semilunar valves open to allow blood ejection.

Valve Functionality

Atrioventricular valves (bicuspid and tricuspid) prevent blood from flowing back into the atria during ventricular systole.
Semilunar valves open when ventricular pressure surpasses aortic pressure, facilitating blood flow into the arteries.
Semilunar valves close when ventricular pressure is lower than aortic pressure to avoid backflow.

Final Notes on Blood Flow

The cycle is continuous, with blood returning to the atria during diastole.
Atrial contraction helps deliver the final amount of blood into the ventricles.
Heart sounds, described as "thump-thump," result from the closure of valves throughout the cardiac cycle.

Summary of Heart Sounds

The first heart sound occurs with the closure of the atrioventricular valves.
The second heart sound is produced by the closing of the semilunar valves.
The average heart rate is approximately 70 beats per minute.

Heartbeat Control Mechanism

Cardiac muscles possess myogenic properties, allowing them to autonomously generate electrical impulses.
Electrical excitation waves throughout the heart chambers promote contraction and facilitate effective blood circulation.

Sinoatrial Node (SA Node)

Acts as the heart's natural pacemaker, establishing the rhythm for heartbeats.
Initiates electrical impulses that propagate through the atrial walls.
Triggers atrial systole, leading to blood being pushed into the ventricles.

Atrioventricular Node (AV Node)

Introduces a delay in the electrical signal received from the SA node.
This delay ensures that the atria contract completely before ventricular contraction begins.
Prevents concurrent contraction of atria and ventricles, crucial for maintaining proper blood flow dynamics.

Bundle of His

Transmits electrical impulses from the AV node to the heart's apex.
Encased in an insulating layer to ensure that ventricles contract only after the signal reaches the apex.
Facilitates effective blood ejection from the lower chambers of the heart.

Purkinje Fibers

Extend from the heart's apex into the ventricular walls to distribute electrical impulses.
Stimulate contraction in the ventricles, known as ventricular systole.
Ensure efficient blood pumping through the aorta and pulmonary artery.

Overall Process

The heartbeat initiates at the SA node, followed by a crucial delay at the AV node.
Impulses travel through the Bundle of His and Purkinje fibers, coordinating a rhythmic contraction.
This well-orchestrated system optimizes blood circulation within the body.

Heart Structure and Function

Understanding various heart diagrams is crucial for success in exams.
The heart contains four chambers: two atria (upper) and two ventricles (lower).
Heart diagrams are often mirrored; the left and right sides may appear opposite to the viewer.
A septum separates the left and right sides; during fetal development, it has a hole to enhance blood flow.

Chambers of the Heart

Right Atrium receives deoxygenated blood from the body through the vena cava.
Right Ventricle pumps deoxygenated blood to the lungs via the pulmonary artery.
Left Atrium collects oxygenated blood from the lungs through pulmonary veins.
Left Ventricle distributes oxygenated blood to the body through the aorta.
The left ventricular wall is thicker than the right to accommodate higher pressure during systemic circulation.

Blood Vessels

Vena Cava has two parts: superior (from upper body) and inferior (from lower body), transporting deoxygenated blood to the right atrium.
Pulmonary Artery is unique as the only artery carrying deoxygenated blood from the heart to the lungs.
Pulmonary Veins carry oxygenated blood from the lungs back to the left atrium; these veins are uncommon for carrying oxygen-rich blood.
Aorta is the largest artery, featuring elastic walls to withstand high blood pressure generated by heart contractions.

Valves

Tricuspid Valve is situated between the right atrium and ventricle; it prevents backflow into the atrium during ventricular contraction.
Semilunar Valves are positioned at the right ventricle exit; they stop backflow into the ventricle after blood is ejected into the pulmonary artery.
Bicuspid Valve (Mitral Valve) is located between the left atrium and ventricle; it prevents backflow when the left ventricle contracts.

Blood Flow Pathway

Blood flow starts as deoxygenated blood enters the heart through the vena cava, moves to the right atrium, and then through the tricuspid valve into the right ventricle.
It is then pumped through the semilunar valve into the pulmonary artery and transported to the lungs for gas exchange and oxygenation.
Oxygenated blood returns via the pulmonary veins into the left atrium, passing through the bicuspid valve into the left ventricle.
The left ventricle then ejects blood through the semilunar valve into the aorta, distributing oxygenated blood throughout the body.

Summary of Blood Circulation

Blood circulation follows this loop: deoxygenated blood enters via vena cava → right atrium → right ventricle → lungs via pulmonary artery → oxygenated blood returns via pulmonary veins → left atrium → left ventricle → aorta → body.

Structure of the Human Heart

Comprised of cardiac muscle, which is distinct to the heart and exhibits myogenic contraction, functioning independently of external stimuli.
Cardiac muscle maintains function without fatigue as long as it receives sufficient oxygen and glucose.

Coronary Arteries

Supply oxygen-rich blood to cardiac muscle.
Blockages can result in myocardial infarction, leading to tissue death and potential heart failure.

Chambers of the Heart

Consists of four chambers: left atrium, right atrium, left ventricle, right ventricle.
Atria are the upper chambers with thinner walls, responsible for receiving and transferring blood to ventricles primarily by gravity.
Ventricles are lower chambers with thicker walls, built to pump blood against gravitational forces.

Ventricles

Right ventricle possesses a thinner wall, pushing blood to the lungs at lower pressure to protect against lung capillary damage.
Left ventricle has a thicker wall, necessary for generating high pressures to distribute oxygenated blood throughout the body.

Major Blood Vessels

Aorta is the main artery, conveying oxygenated blood from the left ventricle to the systemic circulation.
Pulmonary arteries transport deoxygenated blood from the right ventricle to the lungs for oxygenation.
Superior vena cava (from the upper body) and inferior vena cava (from the lower body) return deoxygenated blood to the right atrium.
Pulmonary veins carry oxygenated blood from the lungs back to the left atrium.

Heart Valves

Two main sets of valves: semilunar valves located between ventricles and arteries, and atrioventricular valves situated between atria and ventricles.
Atrioventricular valves include the bicuspid (mitral) valve on the left and the tricuspid valve on the right, characterized by their two and three flaps, respectively.
Valves ensure unidirectional blood flow, opening and closing in response to pressure changes within the heart.

Septum

A muscular wall that divides the heart into left and right sides, preventing the intermingling of oxygenated and deoxygenated blood.
Essential for maintaining concentration gradients required for efficient gas exchange at the cellular level.

Summary

Key structural components: four chambers (left/right atria and left/right ventricles) and four major blood vessels (aorta, pulmonary artery, pulmonary veins, vena cava).
Coronary arteries are crucial for supplying oxygenated blood to heart tissue.
Valves regulate blood flow direction, promoting efficient cardiac circulation.

Cardiac Cycle Overview

The cardiac cycle is the series of events in the heart that facilitate blood flow, characterized by changes in pressure and volume.
Key stages are diastole (relaxation), atrial systole (atria contraction), and ventricular systole (ventricles contraction).

Phases of the Cardiac Cycle

Diastole: A state of relaxation where both atria and ventricles fill with blood, leading to increased volume and rising pressure in the atria.
Atrial Systole: Atria contract, reducing their volume and elevating pressure, which opens the atrioventricular (AV) valves to allow blood flow into the ventricles.
Ventricular Systole: Ventricles contract from the bottom upwards, resulting in decreased volume and increased pressure, closing the AV valves and opening semilunar valves to eject blood into the pulmonary artery and aorta.

Cardiac Output

Cardiac output is the volume of blood ejected from a ventricle per minute.
Formula: Cardiac Output = Heart Rate x Stroke Volume.
Heart Rate refers to beats per minute; Stroke Volume is the amount of blood pumped with each heartbeat.

Valves in the Heart

Heart contains two sets of valves: semilunar valves (between ventricles and arteries) and atrioventricular valves (between atria and ventricles).
Atrioventricular valves open when atrial pressure exceeds ventricular pressure, consisting of the bicuspid (two flaps) and tricuspid (three flaps) valves.
Semilunar valves open when ventricular pressure surpasses arterial pressure, preventing backflow into the ventricles after ejection.

Pressure and Volume Changes

The cardiac cycle features significant pressure and volume fluctuations, ensuring one-way blood flow.
Pressure rises during chamber contraction and falls during relaxation, which regulates valve operation.

Graph Interpretation

Graphs may illustrate pressure variations throughout the cardiac cycle.
Understanding when valves open and close hinges on monitoring pressure levels across heart chambers.
AV valves open when atrial pressure exceeds ventricular pressure, while semilunar valves open with higher ventricular pressure compared to arterial pressure.

Atypical Heart Rate Example

An example involved a dog with a heart rate of 214 beats per minute during exercise, with a cycle duration of 0.28 seconds.
Heart rate can be computed using the formula: Heart Rate = 60 seconds / Cycle Duration.

Study Resources

Flashcards are available to help students memorize key points related to the cardiac cycle and A-Level biology topics.

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