physio - block 2 heart Flashcards
Threshold level of heart
-65
Action potential looks like
At the initiation of the action potential, the fast sodium channels open first, followed later by the opening of the slow calcium channels.
ventricle plateau level?
During which phase of the ventricularaction potential is the conductance to Ca2+ highest?
the conductance to Ca2+ increases transiently. Ca2+ that enters the cell during the plateau is the trigger that releases more Ca2+ from the sarcoplasmic reticulum (SR) for the contraction.
Phase 4 depolarization - NA+ inward current SA nodal
is responsible for the pacemaker property of sinoatrial (SA) nodal cells. It is caused by an increase in Na+ conductance and an inward Na+ current (If), which depolarizes the cell membrane.
Action potential in atria, ventricles and purkinje due to?
action potential in the atria,ventricles, and Purkinje fibers is the result of a fast inward Na+ current. The upstroke of the action potential in the sinoatrial (SA) node is the result of an inward Ca2+ current. The plateau of the ventricular action potential is the result of a slow inward Ca2+ current. Repolarization in all cardiac tissues is the result of an outward K+ current.
The upstroke of the action potential in the sinoatrial (SA) node
is the result of an inward Ca2+ current.
T tubules and the heart? Is it calcium or sodium
is
membrane potential (threshold level) at which the S-A node discharges?
sinus fibers exhibit self-excitation from inward leaking of sodium ions.
-40, resting -55
CARDIAC muscle resting membrane - -85
PR interval?
The cardiac action potential passes through the AV node
The mitral and aortic valves are closed
during isovolemic con- traction, which occurs after the QRS complex has begun.
The second heart sound occurs
at the end of systole.
A 66-year-old man with hypertension is prescribed a drug that inhibits depolarization of the sinoatrial (SA) node of the heart, thereby decreasing impulse conduction of the atria and ventricles. What is the most likely mechanism of action of this drug?
Select one:
a. Voltage-dependent Na+ channel agonist
b. Voltage-dependent K+ channel antagonist
c. β 1 adrenergic agonist
d. Funny (f) channel agonist
e. β 2 adrenergic antagonist
f. Voltage-dependent Ca2+ channel antagonist
f. Voltage-dependent Ca2+ channel antagonist
What is the normal total delay of the cardiac impulse in the A-V node plus bundle?
.13
Which of the following structures will have the slowest rate of conduction of the cardiac action potential?
AV bundle
The atrial and ventricular muscles have a relatively rapid rate of conduction of the cardiac action potential, and the anterior internodal pathway also has fairly rapid conduction of the impulse. However, the A-V bundle myofibrils have a slow rate of conduction because their sizes are considerably smaller than the sizes of the normal atrial and ventricular muscle. Also, their slow conduction is partly caused by diminished numbers of gap junctions between successive muscle cells in the conducting pathway, causing a great resistance to conduction of the excitatory ions from one cell to the next
What is the normal total delay of the cardiac impulse in the A-V node and the A-V bundle system?
.13
What is the difference between EDV and ESV?
end diastolic - after ventricle full - before cxn
end systolic - after cxn- what’s left in ventricle
The EDV is the filled volume of the ventricle prior to contraction and the ESV is the residual volume of blood remaining in the ventricle after ejection. In a typical heart, the EDV is about 120 mL of blood and the ESV about 50 mL of blood. The difference in these two volumes, 70 mL, represents the SV.V.
ventricles are totally depolarized when?
ST segment
two P waves before QRS means?
reduced conduction thru AV node
pulse pressure is determined by?
stroke volume
propranolol inhibits?
b1 receptors
drug reduces cardiac output,
72yo can not keep up with exercise routine - because she is on this drug
When is ventricular volume lowest?
right before filling begins - isovolumetric venticular relaxation
cardiac glycosides do what?
increase intercellular ca+ by inhibiting Na+/K pump thereby inhibiting Na+/Ca+ exchange
increase the output force of the heart and increase its rate of contractions by acting on the cellular sodium-potassium ATPase pump. They are selective steroidal glycosides and are important drugs for the treatment of heart failure and cardiac rhythm disorders.
aldosterone and Na+?
response to hemorrhage
Aldosterone is a steroid hormone. Its main role is to regulate salt and water in the body, thus having an effect on blood pressure.
increases sodium and water reabsorption leading to expansion of the extracellular fluid volume.
Aldosterone is an hormone secreted by the outermost portion of the adrenal cortex and participates to regulation of blood pressure by exerting its main effects on the distal nephron.
Aldosterone excess, whether from genetic causes or primary aldosteronism (hyperplasia or aldosterone-secreting adenomas), is well documented to cause hypertension. Hypertension, in turn, has significant adverse effects on the cardiovascular system, including left ventricular hypertrophy and cardiac fibrosis.
ADH?
when blood volume low, ADH is produced, to have aquaporins inserted in tubules to uptake more h20
increases phosphorylation of phospholamben?
increases contractility
diastasis
is the middle stage of diastole during the cycle of a heartbeat, where the initial passive filling of the heart’s ventricles has slowed, but before the atria contract to complete the active filling.
A 63-year-old woman with congestive heart failure is given digitalis. Positive inotropic drugs can reduce ischemic cardiac pain (angina) in a dilated failing heart by doing which of the following?
a. Decreasing preload
In heart failure, positive inotropic agents reduce oxygen demand by reducing end- diastolic volume (preload) and thus the wall stress that must be developed by the heart with each beat. Reducing volume decreases wall stress because, according to the law of Laplace, the wall stress is proportional to the product of force and radius (which is proportional to ventricular volume).
Atrial fibrillation
is an arrhythmia in which the electrical activity of the atrium becomes disorganized and therefore unable to produce a coordinated atrial contraction. The absence of an atrial pulse reduces the emptying of the atria during diastole and results in an enlarged left atrium and increased left atrial pressure. The venous A wave represents atrial contraction and disappears due to the absence of an atrial beat. Decreased filling of the heart results in a decrease in stroke volume. Heart rate increases because the continuous electrical activity of the atria initiates a high rate of ventricular activity. Systemic blood pressure typically falls because of inadequate filling of the ventricles and the resulting decrease in stroke volume.
Atrial fibrillation
Which of the following is most likely to accompany this condition?
a. An increased left atrial pressure
is an arrhythmia in which the electrical activity of the atrium becomes disorganized and therefore unable to produce a coordinated atrial contraction. The absence of an atrial pulse reduces the emptying of the atria during diastole and results in an enlarged left atrium and increased left atrial pressure. The venous A wave represents atrial contraction and disappears due to the absence of an atrial beat. Decreased filling of the heart results in a decrease in stroke volume. Heart rate increases because the continuous electrical activity of the atria initiates a high rate of ventricular activity. Systemic blood pressure typically falls because of inadequate filling of the ventricles and the resulting decrease in stroke volume.
A person’s electrocardiogram (ECG) has no P wave, but has a normal QRS complex and a normal T wave. Therefore, his pacemaker is located in the
AV node
The absent P wave indicates that the atrium is not depolarizing and, therefore, the pacemaker cannot be in the sinoatrial (SA) node. Because the QRS and T waves are normal, depolarization and repolarization of the ventricle must be proceed- ing in the normal sequence. This situation can occur if the pacemaker is located in the atrioventricular (AV) node. If the pacemaker were located in the bundle of His or in the Purkinje system, the ventricles would activate in an abnormal sequence (depending on the exact location of the pacemaker) and the QRS wave would have an abnormal configu- ration. Ventricular muscle does not have pacemaker properties.
The ventricles are completely depolarized during which isoelectric portion of the electrocardiogram (ECG)?
ST segment
The PR segment (part of the PR interval) and ST segment are the only portions of the electrocardiogram (ECG) that are isoelectric. The PR interval includes the P wave (atrial depolarization) and the PR segment, which represents con- duction through the atrioventricular (AV) node; during this phase, the ventricles are not yet depolarized. The ST segment is the only isoelectric period when the entire ventricle is depolarized.
Heart rate is determined by the formula 60/R-R interval,
this guy’s HR is
R-R interval of 0.55 sec.
and the heart rate for this patient is 109 beats/ min. is is a fast heart rate, which would occur during fever. A trained athlete has a low heart rate. Excess parasympathetic stimulation and hyperpolarization of the S-A node both decrease heart rate.
When recording lead aVL on an EKG, the positive electrode is the
left arm
A 30-year-old female patient’s electrocardiogram (ECG) shows two P waves preceding each QRS complex. The interpretation of this pattern is
decreased conduction through the AV node
When recording lead II on an EKG, the positive electrode is the
left leg
Which of the following conditions will usually result in right axis deviation in an EKG?
Pulmonary hypertension
left axis deviation?
Systemic hypertension
Aortic valve stenosis and aortic valve regurgitation also result in a large left ventricle and left axis devia- tion.
Systemic hypertension results in a left axis deviation because of the enlargement of the left ventricle. Aortic valve stenosis and aortic valve regurgitation also result in a large left ventricle and left axis deviation. Excessive abdominal fat, because of the mechanical pressure of the fat, causes a rotation of the heart to the left resulting in a leftward shift of the mean electrical axis.
