Cardiovascular System Physiology Set 1

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Physiology (Cardio-Vascular System Set 1)

MCQ

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1. About the pacemaker potential, all the following are true except :

A) it's amplitude is - 80 to - 90 mv

B) it is unstable during rest

C) its slope is decreased by increased permeability to K+

D) the firing level occurs at a potential difference of about - 45 mv

E) repolarization is one slow phase

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2. Under normal conditions , the capillaries :

A) contain about 25% of the total blood volume

B) have a very rapid flow rate

C) have a higher pressure than that in the arterioles

D) are all opened at rest

E) contain about 5 % of the total blood volume

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3. The cardiac muscle fibers :

A) are unstriated muscle fibers

B) form true syncytium

C) are poor in mitochondria

D) have low resistance bridges & tight gap junctions

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4. The action potential of cardiac muscle differs from that
of skeletal muscles in:

A) it is propagated more slowly

B) it is shorter in duration

C) it has a higher amplitude

D) it has no plateau

E) all of the above

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5. Myocardial contractility is best correlated with the
intracellular concentration of :

A) Na+

B) K+

C) Ca++

D) Cl

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6. The fibers of the A-V bundle & its branches :

A) conduct impulses very slowly

B) are highly contractile

C) are modified muscle fibers

D) are nerve fibers

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7. About the purkinje tissue ,all the following are true except :

A) they are modified myocardial cells

B) they are confined to the ventricles

C) they are primitive nerve tissue

D) they conduct impulses as some nerves

E) they excite the interventricular septum before the ventricular walls

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8. Regarding the S-A node :

A) cells within the S-A node act as heart pace maker because their membrane depolarized to threshold and initiate an action potential

B) acetyl choline increases the slope of the pace - maker potential

C) sympathetic stimulation decreases the slope of the pace - maker potentia

D) the pace - maker cells within the S-A node are neurons rather than myocytes

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9. About the cardiac muscle all the following are true except :

A) It has low electric resistance of the membrane at the intercalated discs

B) It forms true syncytium

C) It obeys the all or none law

D) there is almost a special capillary for each muscle fiber

10 / 25

10. The cardiac muscle is characterized by having all the following
except :

A) intercalated disk connecting ms

B) A T system located at the Z line

C) The same refractory period characteristics as the skeletal ms

D) Acts as a physiological syncytium

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11. Propagation of the action potential through the heart is
fastest in the :

A) SA node

B) atrial muscle

C) AV node

D) purkinje fibers

E) ventricular muscle

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12. In the heart all the following are true except :

A) the right ventricle is thicker than the left ventricle

B) the excitation wave cannot spread directly from the atria to the ventricles

C) contraction normally begins in the right atrium

D) the ventricles contract almost stimultaneously

E) the S.A node is the normal pacemaker

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13. It is impossible to tetanize a heart because :

A) there is a long mechanical refractory period

B) the refractory period and the mechanical contractile response are of almost equivalent duration

C) the heart muscles do not contain Ca ++

D) the mechanical contractile event is usually shorter than the duration of the electrical depolarization

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14. The main function of the cardiac purkinje system is to :

A) prevent premature ventricular beats

B) coordinate the valve movements with myocardial contraction

C) enable all parts of the ventricle to contract simultaneously

D) delay the systole until the ventricles fill

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15. The SA node is the normal pacemaker because of its :

A) rate of impulse discharge

B) location in the atrium

C) neural control

D) muscular structure

E) relative position to the A.V node

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16. The absolute refractory period in the ventricle :

A) increases during sympathetic stimulation

B) coincides with the phase of rapid depolarization and the plateau

C) corresponds with the whole duration of action potential

D) it is shorter than the ARP of skeletal muscle

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17. The atrio-ventricular valves :

A) have three cusps for each valve

B) their closure is initiated when the ventricular pressure exceeds atrial pressure

C) open by contraction of papillary muscles

D) none of the above

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18. In the heart , all the following are true except :

A) the pericardium limits sudden dilatation of the ventricles

B) the left ventricle gives an aid to the right ventricle

C) the left atrium is the first part to contract

D) the left side of the intervent septum is depolarized before the right side

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19. The S.A node :

A) but not the A.V node receives a parasympathetic nerve supply

B) is connected by a thin band of purkinje fibers to the A.V node

C) has a faster rate of diastolic depolarization during vagal activity

D) has a faster rate of diastolic depolarization at 39 C than at 37 C

E) is a secondary cardiac pacemaker

20 / 25

20. When the bundle of His is completely interrupted ,the :

A) ventricles contract at a rate of 30-40 beats / minutes

B) atria beat irregularly

C) QRS complexes vary in shape from beat to beat .

D) P-R interval remains constant from beat to beat

E) S.A node stops discharging

21 / 25

21. The action potential of the cardiac muscle is characterized by
the presence of plateau which :

A) in the ventricular muscle it reached 100 m sec

B) in the artial muscle, it reached 300 m sec

C) it result from a balance between Ca++ influx and K+ efflux

D) it result from an inflow of Cl- and outflow of bicarbonate ions

22 / 25

22. About the cardiac conductivity, all the following are true except :

A) it is slowest in the A-V node

B) it is maximal in the purkinje fibers

C) it is slowest in the ventricular ms

D) it is decreased by vagal stimulation

E) it occurs through modified cardiac muscle fibers

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23. All the following are correct except

A) the left atrial wall is about the same thickness as the right atrium

B) the left ventricle is separated from the left atrium by a bicuspid valve

C) Purkinje system allows the excitation of all ventricular muscle fibers to occur at nearly the same time

D) the right heart receives oxygenated blood from the four pulmonary veins

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24. The left vent . has a thicker wall than the right ventricle because :

A) it is richer in blood supply

B) it ejects blood through a narrower orifice

C) it ejects a greater cardiac output

D) it ejects blood against a higher pressure

E) it contracts at a higher rate

25 / 25

25. The cardiac tissue with the slowest rhythmicity is the :

A) S.A node without vagal tone

B) S.A node with vagal tome

C) ventricular muscle

D) AV node

E) purkinje fibers

Your score is

The average score is 17%

Cardiovascular System Physiology Set 1

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