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STUDY OF THE EFFECT OF
VARIOUS DRUGS AND IONS
ON THE FROGS HEART
Li Jingxin
Physiologcal Department
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THEORY
Ions 1.The fluids perfusing the heart must contain a proper
balance of the three essential ions i.e. sodium ions,
potassium ions and calcium ions.2. If these three ions are
present proper proportions, theheart is able to maintain its normal
contracti1ity forhours in an oxygenated environment.
3. If the concentrations of ions are abnormal, then theheart
will what happen?
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1). If concentration of these ions is
altered then heart rate andcontractility are changed.
e.g. excess of potassium ions in the
fluids perfusing the heart causes
the heart to become dilated and
slows the heart rate and may stopheart during diastole .
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2).An excess of sodium ions
depresses cardiac function likepotassium ions excess but for
an
entirely different reason. Sodium
ions compete with the calcium ions
at the same point in the excitatory
or contractile process of the heartmuscle .
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3).Excess calcium ions in the fluidsenhance myocardial
contractility .When large amount of calcium ionsare infused into
the experimentalanimals, the heart relaxes lessduring diastole and
eventually stopsin systole (calcium rigor). A
deficiency of calcium ions causescardiac flaccidity.
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Drugs
1.The intrinsic properties of theheart are inf1uenced by
autonomic nervous system.
Sympathetic and parasympathetic
nerve
2.Various drugs acting on specificreceptors present in the heart
also
influence the cardiac activity.
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Acetylcholine(Ach) acts on
the M- receptors present inthe heart and causes the
decrease in the heart rate andcardiac contractility.
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Adrenalin (Adr) acts on alpha
and beta-adrenergic receptors.It has positive chronotropic
(increased heart rate) andpositive inotropic (increased
force of contraction)effects .
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PROCEDURE 1.Expose the frogs heart
As compared to human heart, in the
frogs heart, there are five chambers
ie one ventricle, two atrium, one sinusvenosus ,one truncus
arteriosus
There is no special conducting tissue.
There is no coronary circulation in the
frogs heart
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ventricle
Truncus arteriosus
atrium
sinus venosus
ventricle
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a. The parietal layer of the membranous
pericardium if easily removable but the visceral
layer is firmly attached to the heart muscle.
b. The wall of single ventricle is thicker than
that of atria.
c. The truncus arteriosus lies anteriorly to the
ventricle near it base and divides into two aorta.
d. Sinus venosus lies posteriorly and superior
and inferior vena cava empty into it.
e. The color of the ventricle is seen to become
pale during contraction.
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f. During contraction, size of the ventricle is decreased
and during relaxation size is increased due to distension
g. The two atria are separated from the ventricle by
atrio-ventricular groove.
h. A careful observation will show a white line at the
junction of the sinus and atria.
i. Sequence of heartbeat is the sinus, atria, ventricle
andfinally the truncus arteries.
If we remove the heart from the animals body and
immerse it in Ringer solution placed, the various parts of
the heart are seen to continue to beat in the usual
regularsequence. This indicates that the heartbeat originates
from the heart itself.
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PROCEDURE
2. Connect the heart clip with theapex of the ventricle. Lift
the heartgently by raising the lever and
adjust its position so that thebeating heart produces
goodmovements. Pour Ringer solution
on the heart from time to time .3. Adjust the velocity and
sensitivity ,record normal curve.
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