Heart Part 2 Flashcards
(32 cards)
What occurs in the pacemaker potential step in autorhythmic cells?
Slow Depolarization due to:
- opening of Na+ channels, Closing of K+ channels
- becomes LESS negative
What occurs in the depolarization step in autorhythmic cells?
- Depolarization due to Ca2+ influx
- AP begins when pacemaker reaches -40mV
- Becomes POSITIVE
What occurs in the Repolarization step in autorhythmic cells?
- Ca2+ channels close
- K+ channels open
- Returns to negative
Explain sinoatrial SA node in the sequence of excitation.
- In top right of heart (right atrium), inferior to SVC entrance
- FASTEST node (75 times/min)
Explain Atrioventicular AV node in the sequence of excitation.
- Between Right atrium & left ventricle
- completely depolarizes atrium
- 0.1 second delay is beneficial
- 50 impulses/min
Explain Atrioventicular AV bundle (bundle of His) in the sequence of excitation.
- only electrical pathway between atria & ventricles
- insulate by fibrous skeleton of heart to make sure ventricles depolarize AFTER atria
Explain Right and Left bundle branches in the sequence of excitation.
- carry impulses toward heart apex
Explain the purkinje fibers in the sequence of excitation.
- complete pathway into apex & ventricular walls
- very slow 30 impulses/min (without AV node input)
What is the conduction delay in the heart? Where does ventricular contraction start?
0.22 sec delay between SA node and last ventricular muscle
- starts at apex (bottom of heart)
Explain the innervation of the heart from PSNS and SNS (3)
PSNS
- travels through vagus nerve
- ONLY reduces heart rate
- innervates nodes
SNS
- travels through spinal cord
- increases heart rate AND force of contraction
- innervates muscle fibers + nodes
Where does the stimulus for the heart’s rhythmic contractions comes from?
a pacemaker potential
What do the P, QRS, T wave refer to? how long?
P wave: atrial depolarization (0.08s)
QRS complex: ventricular depolarization (0.08s)
T wave: ventricular repolarization (0.16s)
Explain the ECG intervals
P-R (0.16s)
S-T (0.08s)
Q-T (0.38s)
P-R: start of atrial excitation to ventricular excitation
S-T: Ventricles depolarized
Q-T: start of ventricular depolarization to end of ventricular repolarization
What is the order of ECG heart beat (6)
- Atrium depolarizes, initiated by SA NODE, causes P wave
- With atrial depolarization complete, impulse is delayed at AV NODE
- Ventricular depolarization begins at apex, causing QRS complex. also atrial repolarizes
- Ventricles fully depolarized
- Ventricle repolarizes at apex, causing T wave
- Ventricles fully repolarized
What does systole and diastole refer to? what does our heart spend more time doing?
Systole = contraction
Diastole = relaxation
1/3 time contracting
2/3 time relaxing
Explain the ventricular filling (mid-late diastole) in the phases of the cardiac cycle
- AV valves open, semilunar valves closed
- 80% of blood passively flows into ventricles
- ATRIAL SYSTOLE pushes remained 20%
- End diastolic volume: volume of blood in each ventricle at end of ventricular diastole phase
Explain the ventricular systole phase in the phases of the cardiac cycle
- Atria relax (atrial diastole), ventricles contract
- Increase of ventricular pressure closes AV valves
- Isovolumetric contraction phase: all valves closed
- Ejection phase: ventricular pressure > pressure in arteries = semilunar valves open
- End systolic volume: volume of blood in each ventricle at end of ventricular systole
Explain the isovolumetric relaxtion phase in the phases of the cardiac cycle?
- ventricles relax, blood pushes back against semilunar valves
- Causes dicrotic notch (brief rise in aortic pressure)
Explain S1 and S2 heart sounds
S1 (lub)
- when AV valves close
- signifies beginning of ventricular systole (contraction)
S2 (dub)
- occurs when SL valves close
- signifies beginning of ventricular diastole (relaxation)
What is the equation for Stroke Volume SV
EDV - ESV
What is the equation for ejection fraction EF? What does it mean
SV/EDV
- % of total ventricular volume ejected in 1 contraction
- EF will increase with exercise
What is the equation for cardiac output?
Heart rate x stoke volume
What is cardiac reserve?
- difference between resting & maximal CO
Explain preload in regulation of stroke volume
Preload: degree of stretch of cardiac muscle BEFORE they contract
- exhibit a length-tension relationship
- at rest, cardiac muscle are shorter than optimal length
