Cardiac Cycle and Control Mechanisms

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Questions and Answers

What occurs during atrial systole?

A massive increase in ventricular pressure.

The closure of the aortic valve.

A rapid decrease in pressure.

A very slight increase in pressure. (correct)

What happens immediately after ventricular systole begins?

The aortic valve opens.

Blood flows back into the ventricles.

The atria begin to contract.

The AV valve closes due to increased pressure. (correct)

How is diastolic pressure defined?

The pressure during atrial systole.

The pressure between ventricular contractions. (correct)

The pressure during blood filling in the ventricles.

The pressure when the heart is at rest.

What is the role of the sphygmomanometer in measuring blood pressure?

To occlude blood flow and determine the pressure at which a pulse is first heard. Signup and view all the answers

What sound is typically used to ascertain systolic pressure during measurement?

The sound of blood pulsing through the brachial artery. Signup and view all the answers

What causes the first heart sound ('lubb') during the cardiac cycle?

Closure of the atrioventricular valves Signup and view all the answers

Which of the following accurately describes the sinoatrial node?

It serves as the heart's pacemaker Signup and view all the answers

During which phase does the second heart sound ('dupp') occur?

Start of ventricular diastole Signup and view all the answers

What defines myogenic contraction?

Contraction that occurs rhythmically and automatically Signup and view all the answers

What is primarily responsible for the changes in blood pressure during the cardiac cycle?

Contraction and relaxation of heart chambers Signup and view all the answers

What regulates the rate of heartbeats?

Nerves connected to the sinoatrial node Signup and view all the answers

What is the role of the electrical signal propagated from the sinoatrial node?

To initiate and coordinate cardiac muscle contractions Signup and view all the answers

What causes systolic blood pressure?

Force of blood against arterial walls during heart contractions Signup and view all the answers

What prevents the action potential from traveling directly to the ventricles?

A layer of fibrous tissue Signup and view all the answers

In which order do the events of the cardiac cycle occur?

Atrial systole -> Ventricular systole -> Diastole Signup and view all the answers

What is the role of the sinoatrial node in the cardiac cycle?

To initiate an action potential Signup and view all the answers

When does the atrioventricular valve close during the cardiac cycle?

When pressure increases in the ventricle during ventricular systole Signup and view all the answers

What happens when the pressure in the ventricle becomes less than that in the aorta?

The semilunar valve closes Signup and view all the answers

During which phase does pressure increase in the left atrium?

Atrial systole Signup and view all the answers

How does blood flow from the left atrium to the left ventricle during diastole?

Through passive flow due to pressure difference Signup and view all the answers

What initiates the contraction of the ventricles during the cardiac cycle?

An action potential from the atrioventricular node Signup and view all the answers

Study Notes

Cardiac Cycle

The heart beats with two sounds: “lubb-dupp”.
The first heart sound, “lubb”, is caused by the closure of the atrioventricular valves at the beginning of ventricular systole.
The second heart sound, “dupp”, is caused by the closure of the semilunar valves at the beginning of ventricular diastole.

Control of the Cardiac Cycle

Cardiac muscle is myogenic, meaning it contracts without stimulation.
The sinoatrial node (pacemaker) controls the rate of heartbeat.
The sinoatrial node initiates an action potential that rapidly spreads across the atria, causing atrial systole (contraction).
A layer of fibrous tissue prevents the action potential from directly traveling to the ventricles.
The action potential travels to the ventricles via the atrioventricular node.
The action potential travels down the Purkinje fibers to the apex of the heart, then up the walls of the ventricles, initiating ventricular systole from the apex, pumping all of the blood out of the ventricles.

The Cardiac Cycle

Systole is the contraction of heart muscles.
Diastole is the relaxation of heart muscles.
During diastole, most of the blood flow directly through the atrium to the ventricle.
An action potential from the sinoatrial node causes the left atrium to enter systole, increasing pressure in the atrium and forcing all of the blood into the ventricle.
An action potential from the atrioventricular node causes the ventricle to enter systole, increasing pressure.
When the ventricle contracts, higher pressure in the ventricle closes the atrioventricular valve.
As ventricular pressure continues to increase, the semilunar valve opens, allowing blood to move into the aorta.
When ventricular pressure decreases as the ventricle enters diastole, the semilunar valve closes.
The atrioventricular valve opens when pressure in the ventricle is lower than the atrium.

Measuring Blood Pressure

Blood pressure measurements include systolic pressure (caused by ventricular systole) and diastolic pressure (between ventricular contractions).
Blood pressure is measured in arteries using a sphygmomanometer (blood pressure cuff).
To measure blood pressure, the cuff is inflated, cutting off circulation to the brachial artery in the arm.
The cuff pressure is slowly released until a pulse can be audibly detected with a stethoscope, which is the systolic pressure.

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Description

This quiz covers the cardiac cycle, including the sounds of the heart and the role of the sinoatrial node. It explains how electrical impulses initiate heart contractions and the flow of action potentials through the heart's conduction system. Test your understanding of these crucial heart functions.