Download Mechanical Properties MCQ

2/28/2008
Mechanical Properties
MCQ
1- Regarding the excitation-contraction coupling in
cardiac muscle:
a- Cardiac cells directly trigger Ryanodine (Ry)
channel Ca2+ release.
b- Is an example of Ca induced Ca release (CICR)
as all excitable muscles.
c- Blocked by dihydropyridine (DHP).
d- Calmodulin sufficiently induced relaxation.
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2- The followings are the mechanisms lower intracellular
Ca2+ and produce relaxation EXCEPT:
a- Sarcoplasmic reticulum ATP-dependent Ca2+
reuptake.
b- Na+-Ca2+ exchanger.
c- Calmodulin.
d- Inhibition of Na-K pump.
3- Ca2+ released from Sarcoplasmic reticulum
(SR) in cardiac cells:
a- Binds with tropomyocin to initiate contraction.
b- Partially buffered by mitochondria.
c- Pumped back to SR that inhibited by digitalis.
d. Exchanged with extra- cellular K+.
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4- When a cardiac muscle strip is stretched by a load and
stimulated:
a-
Maximal
developed
tension
occurs
with
maximal stretching length.
b- The tension increases without shortening
causing isometric contraction.
c-
The
muscle
contracts
and
shortens
isotonically with further increase in tension.
d. The length at which the load is lifted is the
afterload.
5- In the whole intact heart all the followings are
correct EXCEPT:
a- The length of the muscle fiber is
proportionate to the end-diastolic volume.
b- The tension developed is proportionate to
the pressure developed in the ventricle..
c- The preload is the degree to which the
myocardium is stretched before it contracts
d. The afterload
pressure.
equals the end diastolic
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6- Regarding the afterload in the whole intact
heart :
a- Is the resistance against which blood is
expelled.
b- It equals the end systolic pressure
c- Approximately equals the aortic pressure.
pressure
d. All of the above.
7- The performance of the cardiac muscle can be measured
by the followings EXCEPT:
a- The ejection fraction (EF).
(EF)
b- The extent of shortening (ΔL) .
c- The velocity of shortening (dl/dt).
d The
dTh rate off frequency
f
(b/ i )
(b/min).
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8- The performance of cardiac muscle is affected
by:
a
a-
Mechanical
determinants
(preload
and
contractility).
b- Heart rate.
c- Contractility that depends on preload and
afterload
d- All of the above
9- Regarding the extent and velocity of shortening of the
cardiac muscle:
a- Increased by increments in preload.
b- Decreased by increments in after-load.
c- Raised by decrease in after-load.
d- All of the above.
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10- In length-tension curve of the cardiac muscle
all of the followings are correct Except:
a-
Increasing
preloads
is
associated
with
increasing in extent of shortening.
b-
Increasing
afterloads
is
associated
with
decreasing in extent of shortening.
c- At the same level of preload and afterload,
c
afterload -ve
ve
inotropic stimulus shifts the curve upwards and
to the left.
d- More shortening occurs with +ve inotropic
stimulus.
11-
The
load-velocity curve
of
the
cardiac
muscle
describes:
a- Direct relation with afterload.
b- Inverse relation with preload.
c- The muscle is faster and can shorten more at
higher preload.
d- The muscle is faster with digitalis when
afterload increased.
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Passive: without stimulation
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Simple Curve
Isometric Contraction
Isotonic Contraction
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Function curve
1
1
Length‐tension curve: Length‐shortening curve.
Length‐tension curve: Load‐shortening curve.
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Effects of alternations of inotropic state (+ve & ‐ve) on length‐tension curve 10