T2: Cardiac Cycle Flashcards
What 3 major types of cardiac muscle is the heart composed of?
- atrial muscle
- ventricular muscle
- specialized excitatory and conductive muscle fibers
What is the structure of cardiac myocytes?
- striated (thin actin and thick myosin fillaments)
- no gap junctions
- intecallated disks
What is the name of the valves seperating the atria and ventricles?
atrioventricular valves
left: mitral valve
right: tricuspid valve
What valve does blood exit the heart through?
- pulmonary valve (to pulmonary trunk)
- aortic valve (to aorta)
What does the cardiac conduction system contain?
- sinoatrial node
- atrioventricular node
- bundle of His (atrioventricular bundle)
- purkinje fibers
What is the pacemaker? What does it do?
- the sinoatrial node
- sends electrical impulses which initiate the heart beat
What does the atrioventricular node do?
delays the SA node’s electrical signal
What does the bundle of His do?
- recieves electrical signals from the AV node
- carries electrical impulses to the Purkinje fibers
What are Purkinje fibers? What are their functions?
- branches of specialized nerve cells
- send electrical impulses to the right and left ventricles
What does each cardiac cycle have? What phases? What occurs during each phase?
Diastolic phase:
- relaxation
- filling of heart with blood
Systolic phase:
- contraction
- exiting of blood
Explain the steps of the cardiac cycle?
1) atrial systole
2) ventricular systole
3) atrial diastole
4) ventricular diastole
What are the three phases of ventricular systole?
1) isovolumic contraction (pressure builds in the ventricle)
2) ventricular ejection (ventricles eject blood)
3) isovolumic relaxation
What happens during ventricular contraction?
atria relax (atrial diastole)
State, in order, the different phases of the cardiac cycle.
- atrial diastole
- atrial systole
- isovolumic contraction
- ventricular ejection
- isovolumic relaxation
- ventricular filling
Approximately how long is a heart cycle?
0.8 seconds
Why is diastole important?
- for chambers to refill again (without it, there wouldn’t be blood to push out during the next systole)
- essential for proper blood circulation
- essential for the nourishing of the body’s tissues and organs
What are the 3 stages of a single heart beat?
- atrial depolarization
- ventricular depolarization
- atrial and ventricular repolarization
What nervous system controls the firing of the sinus node to trigger the start of the cardiac cycle?
autonomic nervous system
What is an electrocardiogram (ECG)?
a graphic record of the electrical activities of the heart, as monitored at specific location son the body surface
What are ECG’s used for?
diagnosing cardiac arrhythmias
What are cardiac arrhythmias?
abnormal patterns of cardiac electrical activity
State the different parts of the ECG.
1) P wave
2) PR interval
3) QRS complex
4) ST segment
5) T wave
What does the P-wave refer to?
- atrial depolarization
- SA node trigerring
What does the PR-inteval refer to?
- delay of the AV node
- alows filling of ventricles
What does the QRS-complex refer to?
- depolarization of the ventricles
- triggers the main pumping contractions
What does the ST-segment refer to?
- beginning of ventricle repolarization
- should be flat
What does the T-wave refer to?
- ventricular repolarization
Does the heart undergo tetany or summation?
NO!
no tetany or summation possible as the heart has a long absolute REFRACTORY PERIOD.
What is tetany?
involuntary muscle contractions and overly stimulated peripheral nerves
What is summation?
the additive effect of electrical impulses in multiple numbers coming on a neuromuscular junction
What does the “starling’s law” state?
the more the heart is filled during diastole, the greater the volume pumped out.
What is “cardiac output”?
the amount of blood that the heart pumps in a unit of time (usually ml or L per minute)
What is “stroke volume”?
the amount of blood pumped out of the heart with each individual beat of the heart
How is cardiac output calculated?
stroke volume x heart rate
- units: ml/minute
What is “tachycardia”?
abnormally fast heart beat
What is “bradycardia”?
abnormally slow heart beat
What are “atrial fibrillations”?
- the irregular contraction of atria
- blood cannot effectively flow out of atria
What are “ventricular fibrillations”?
- the irregular contraction of ventricles
- blood cannot effectively flow out of ventricles
- leads to death unless corrected
