Chapter 20 Physiology (cardiac cycle)

Created by lshows 

Upgrade to
remove ads

What is the cardiac cycle?

All of the events that amke up one heart beat (lub-dub)

What is the average duration of the cardiac cycle?

*~0.75 - 1 second in length

***This time frame can vary widely

How is heart rate calculated?

*Heart rate is dictated by the cardiac cycle

*Divide cardiac cycle time into 60

EXAMPLE:
-Cardiac cycle is 0.75 seconds long
-60 seconds in a minute
-Divide 60 by 0.75 to get heart rate

60/0.75= 80 beats/minute

Approximately how much of the cardiac cycle does the heart spend in systole?

~ 1/3 of its time

Approximately how much of the cardiac cycle does the heart spend in diastole?

~ 2/3 of its time

What does systole mean?

Contracting

What does diastole mean?

Relaxing

What is atrial systole?

Time the atria are contracting

What is ventricular systole?

Time the ventricles are contracting

***If the term systole is used without specifying atrial or ventricular, ventricular systole is ALWAYS implied

What is atriole diastole?

Time the atria are relaxing

What is ventricular diastole?

Time the ventricles are relaxing

******If the term diastole is used without specifying atrial or ventricular, ventricular diastole is ALWAYS implied

What are the five periods of the cardiac cycle?

1. Isovolumic contraction (systole)
2. Period of ejection (systole)
3.Isovolumic relaxation (diastole)
4. Passive ventricular filling (diastole)
5. Active ventricular filling (diastole)

***The cardiac cycle only focuses on events occurring in the ventricles, NOT atria)

What occurs during the isovolumic contraction period?

*Ventricles begin to contract, causing vetricular pressure to increase

*AV valves snap shut

*ALL HEART VALVES ARE NOW CLOSED so no blood flow out of the ventricle

***Blood volume does not change (isovolumic)

***First heart sound is heard (S₁)

***AV insufficiency can be heard at this time

What occurs during the period of ejection?

*First heart sound (S₁) still evident

*Further contraction of ventricles causes further increase in ventricular pressure

*Increase in pressure forces the pulmonary valve and aortic valve to open

*Blood empties from ventricles into the pulmonary trunk and aorta

*AV insufficiency can still be heard

*Semilunar stenosis is now heard

What is stroke volume?

*Stroke volume (SV) is the volume of blood pumped from one ventricle of the heart with each beat

Do the ventricles pump the same or different quantities of blood with each beat?

*Approximately the same amount of blood is pumped by each ventricle, even though the ventricles apply vastly different amounts of pressure when contracting

What is the end-diastolic volume?

*End-diastolic volume (EDV) is the volume of blood present in each ventricle at the end of diastole (relaxing) and beginning of systole (contracting)

What is the average value of end-diastolic volume?

~ 120 ml

What is the average stroke volume?

~ 70 ml is ejected by EACH ventricle with each heart beat

What is the ejection fraction?

*Percent of end-diastolic volume (EDV) left in each ventricle after the stroke volume (SV) has been ejected

*Based on normal EDV and SV values, the ejection fraction is 55%

How is the ejection fraction calculated?

Stroke volume (SV) = 70 ml
End-diastolic volume (EDV) = 120 ml

Divide SV by EDV x 100

(70ml / 120ml) x 100 = 55%

What is end-systolic volume?

*End-systolic volume is the volume of blood left in the ventricle at the end of systole (contacting) and the beginning of diastole (relaxing)

What is the average value of end-systolic volume?

~ 50ml

How is end-systolic volume calculated?

(End-diastolic volume) - (Stroke Volume) = End-systolic volume

(120 ml) - (70 ml) = 50 ml

What occurs during the isovolumic relaxation period?

*Relaxation of the ventricles

*Ventricular pressure decreases below pulmonary trunk and aortic pressures

*Semilunar valves snap shut

*ALL HEART VALVES ARE NOW CLOSED (isovolumic)

*Second heart sound (S₂) is heard ("dub")

*Semilunar insufficiency is heard at this time

What occurs during the passive ventricular filling period?

*Pressure within relaxed ventricles is lower than atrial pressure (because the atria are currently filling with blood)

*AV valves open (but atria is not yet contracting)

*Blood flows passively from the atria to the ventricle

*Semilunar insufficiency can still be heard

*AV stenosis heard at this time

What occurs during the active ventricular filling period?

*Atria contract and actively fill ventricles with blood

*At the end of this period, ventricles usually contain ~ 120 ml of blood (end-diastolic volume)

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set