physio - block 2 heart

Question 1

Threshold level of heart

Answer 1

-65

Question 2

Action potential looks like

Answer 2

At the initiation of the action potential, the fast sodium channels open first, followed later by the opening of the slow calcium channels.

Question 3

ventricle plateau level?

During which phase of the ventricularaction potential is the conductance to Ca2+ highest?

Answer 3

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.

Question 4

Phase 4 depolarization - NA+ inward current SA nodal

Answer 4

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.

Question 5

Action potential in atria, ventricles and purkinje due to?

Answer 5

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.

Question 6

The upstroke of the action potential in the sinoatrial (SA) node

Answer 6

is the result of an inward Ca2+ current.

Question 7

T tubules and the heart? Is it calcium or sodium

Answer 7

is

Question 8

membrane potential (threshold level) at which the S-A node discharges?

sinus fibers exhibit self-excitation from inward leaking of sodium ions.

Answer 8

-40, resting -55

CARDIAC muscle resting membrane - -85

Question 9

PR interval?

Answer 9

The cardiac action potential passes through the AV node

Question 10

The mitral and aortic valves are closed

Answer 10

during isovolemic con- traction, which occurs after the QRS complex has begun.

Question 11

The second heart sound occurs

Answer 11

at the end of systole.

Question 12

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

Answer 12

f. Voltage-dependent Ca2+ channel antagonist

Question 13

What is the normal total delay of the cardiac impulse in the A-V node plus bundle?

Answer 13

.13

Question 14

Which of the following structures will have the slowest rate of conduction of the cardiac action potential?

Answer 14

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

Question 15

What is the normal total delay of the cardiac impulse in the A-V node and the A-V bundle system?

Answer 15

.13

Question 16

What is the difference between EDV and ESV?

end diastolic - after ventricle full - before cxn

end systolic - after cxn- what’s left in ventricle

Answer 16

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.

Question 17

ventricles are totally depolarized when?

Answer 17

ST segment

Question 18

two P waves before QRS means?

Answer 18

reduced conduction thru AV node

Question 19

pulse pressure is determined by?

Answer 19

stroke volume

Question 20

propranolol inhibits?

Answer 20

b1 receptors

drug reduces cardiac output,

72yo can not keep up with exercise routine - because she is on this drug

Question 21

When is ventricular volume lowest?

Answer 21

right before filling begins - isovolumetric venticular relaxation

Question 22

cardiac glycosides do what?

increase intercellular ca+ by inhibiting Na+/K pump thereby inhibiting Na+/Ca+ exchange

Answer 22

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.

Question 23

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.

Answer 23

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.

Question 24

ADH?

Answer 24

when blood volume low, ADH is produced, to have aquaporins inserted in tubules to uptake more h20

Question 25

increases phosphorylation of phospholamben?

Answer 25

increases contractility

Question 26

diastasis

Answer 26

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.

Question 27

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?

Answer 27

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).

Question 28

Atrial fibrillation

Answer 28

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.

Question 29

Atrial fibrillation

Which of the following is most likely to accompany this condition?

a. An increased left atrial pressure

Answer 29

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.

Question 30

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

Answer 30

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.

Question 31

The ventricles are completely depolarized during which isoelectric portion of the electrocardiogram (ECG)?

Answer 31

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.

Question 32

Heart rate is determined by the formula 60/R-R interval,

this guy’s HR is

R-R interval of 0.55 sec.

Answer 32

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.

Question 33

When recording lead aVL on an EKG, the positive electrode is the

Answer 33

left arm

Question 34

A 30-year-old female patient’s electrocardiogram (ECG) shows two P waves preceding each QRS complex. The interpretation of this pattern is

Answer 34

decreased conduction through the AV node

Question 35

When recording lead II on an EKG, the positive electrode is the

Answer 35

left leg

Question 36

Which of the following conditions will usually result in right axis deviation in an EKG?

Answer 36

Pulmonary hypertension

Question 37

left axis deviation?

Systemic hypertension

Aortic valve stenosis and aortic valve regurgitation also result in a large left ventricle and left axis devia- tion.

Answer 37

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.