Physiology of the Cardiovascular & Pulmonary Systems Flashcards
Why does the first part of the P-wave represent R atrial depolarization and the second part L atrial depolorization
- Sinus node is located n the R atrium and therefore begins to depolarize before the L atrium & finishes earlier as well
What is the role of the Bachman bundle
- Allows for rapid activation of the L atrium from the R
- May be implicated in atrial fibrillation
What is the pause the separates the conduction from the atria into the ventricles
- Wave of depolarization is briefly held up at the AV node
- Permits the atria to empty their volume of blood completely into the ventricles before the ventricles contract
- Seen on EKG/ECG following the P-wave
What is repolarization
- After myocardial cells depolarize, they pass through a brief refractory period during which they are resistant to further stimulation
Describe the difference b/w the PR interval and PR segment
- Interval: includes the P-wave & the horizontal line connecting it to the QRS complex; measures the time from the start of atrial depolarization to the start of ventricular depolarization
- Segment: measures the time from the end of atrial depolarization to the start of ventricular depolarization
What does the ST segment measure
- Measures the time from the end of ventricular depolarization to the start of ventricular repolarization
What does the QT interval measure
- Measures the time from the beginning of ventricular depolarization to the end of ventricular repolarization
What does the QRS interval measure
- Measures the duration of ventricular depolarization
What 3 factors effect stroke volume
- Preload
- Contractility
- Afterload
Describe the sympathetic and parasympathetic impact on heart rate
- Sympathetic: release of epinephrine from the adrenal medulla of the adrenal gland and norepinephrine from the sympathetic axons open channels of the pacemaker cells of the SA node and increase the rate of depolarizations, resulting in an increase in heart rate
- Parasympathetic: release of acetylcholine released by vagus nerve endings that bind to acetylcholine receptors, slowing down the rate of action potential production at the level of the SA node, thereby depressing heart rate
What is preload correlated with
- End diastolic volume (EDV) which is the max amount of blood that can be in the ventricles at the end of diastole immediately before contraction
What is the Frank-Starling mechanism of preload
- Strength of ventricular contraction increases as the pre contractile myocardial cell length increases (influenced by ventricular filling)
What intrinsic factors effect contractility
- Degree of myocardial stretch caused by change sin the EDV
- Force frequency relationships: higher HR (>120 bpm) and increased availability of calcium ions allows for excitation-contraction coupling & a resultant stronger contraction
What extrinsic factors effect contractility
- Epinephrine from adrenal medulla & norepinephrine from sympathetic nerve endings produce pos. ionotropic effect (increased contractility) by promoting an influx of calcium available to the sarcomeres of the myocardial cells
- Reduction in sympathetic stimulation/reduction in HR results in reduced myocardial contractility
Describe what afterload is
- Pressure generated within the ventricle must exceed the pressure within the systemic vasculature
-Total peripheral resistance: pressure within arterial system during the diastolic phase of the cardiac cycle while the heart is filling; presents a hindrance to the ejection of blood from the ventricles - Afterload is inversely proportional to stroke volume (increase in after load/total peripheral resistance reduces the amount of blood ejected with each contraction)
What si the best indicator of cardiac function
- Ejection fraction
- Percentage of the volume of blood ejected out of the ventricles relative to the volume of blood received by the ventricles before contraction
- EF = stroke volume/end diastolic volume
Describe normal, reduced, and preserved ejection fraction
- Normal = 60-70%
- Heart failure w/reduced EF = systolic dysfunction (can’t squeeze)
- Heart failure w/preserved EF = diastolic dysfunction (can’t fill/stretch): due to HTN, hypertrophy
What is end systolic volume
- Volume of blood that remains in the ventricle following contraction
- ~30% of the end diastolic volume