Lesson 5

What is the mechanical activity of the heart?

Alternating contraction and relaxation (systole and diastole).

What is the mechanical activity of the heart a consequence of?

Electrical activity.

What is the cardiac cycle?

Time between one systole and the next.

What does one cardiac cycle include?

All events of one heartbeat.

What phases make up the cardiac cycle?

Atrial systole/diastole and ventricular systole/diastole.

Do atria and ventricles contract at the same time?

No, due to AV node delay.

What happens when a heart chamber contracts?

Pressure inside increases.

What drives blood flow in the heart?

Movement from high to low pressure.

How many phases does the cardiac cycle have?

5

What are the phases of the cardiac cycle?

Atrial contraction, Isovolumetric contractrion, Ventricular ejection, Isovolumetric relaxation, Ventricular filling

What is atrial systole or contraction phase?

Doplarization of SA node causes depolarization and Contraction of atria and opening of AV valve pushing blood into ventricles

What marks atrial depolarization?

P wave.

How much blood does atrial systole add?

~25 mL to each (to the 105ml that ar already in the ventricle)

What is end-diastolic volume (EDV)?

Volume in ventricle at end of filling (~130 mL).

What is ventricular systole?

Contraction of ventricles.

What is ventricular diastole?

Relaxation of ventricles.

What is isovolumetric contraction?

Early ventricular contraction with all valves closed.

What happens to volume during isovolumetric contraction?

Remains constant

What happens to pressure during this phase?

Increases.

What heart sound begins here?

First heart sound (S1).

What causes S1?

Closure of AV valves.

What is the ejection phase?

semilunar valves open And Blood is expelled from ventricles to the aorta and pulmonary arteries

What causes semilunar valves to open?

Ventricular pressure exceeds arterial pressure.

Where does blood go during ejection?

Aorta and pulmonary arteries.

How much blood is ejected per beat?

~70 mL.

What is stroke volume (SV)?

EDV − ESV.

What is end-systolic volume (ESV)?

Blood remaining after contraction (~60 mL).

What closes semilunar valves?

Arterial pressure exceeding ventricular pressure.

What heart sound is produced here?

Second heart sound (S2).

What causes S2?

Closure of semilunar valves.

What is isovolumetric relaxation?

Relaxation phase with all valves closed.

What happens to volume?

Remains constant.

What happens to pressure?

Decreases.

What happens when ventricular pressure falls below atrial pressure?

AV valves open.

What phase begins then?

Ventricular filling.

What is ventricular filling?

Blood flows from atria to ventricles.

How much filling occurs passively?

~75%.

What drives ventricular filling?

Atrial pressure > ventricular pressure.

What happens at the end of relaxation period?

New cardiac cycle begins.

How long is atrial systole?

~0.1 seconds.

How long is ventricular systole?

~0.3 seconds.

How long is relaxation period?

~0.4 seconds.

What happens to relaxation time at high heart rate?

It shortens significantly.

What is the relationship between EDV, ESV, and SV?

SV = EDV − ESV.

What is EDV?

Maximum ventricular volume.

What is ESV?

Minimum ventricular volume after systole.

Does the heart empty completely?

No, blood always remains (ESV).

What causes heart sounds?

Turbulent blood flow from valve closure.

What is S1?

Closure of AV valves ("lubb").

What is S2?

Closure of semilunar valves ("dupp").

What is S3?

Sound from rapid ventricular filling.

What is S4?

Sound from atrial contraction.

Are S3 and S4 normally heard?

No, usually not audible.

What is auscultation?

Listening to heart sounds with stethoscope.

Where are heart sounds best heard?

At specific chest locations, not exactly at valves.

What are heart murmurs?

Abnormal turbulent blood flow sounds.

What can murmurs indicate?

Valve problems or abnormal flow.

Are murmurs always pathological?

No, often normal in children.

What is the Wiggers diagram?

Graph showing all events during cardiac cycle.