STUDY OF THE EFFECT OF
VARIOUS DRUGS AND IONS
ON THE FROG’S HEART
Li Jingxin
Physiologcal Department
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, the heart is able to maintain its
normal contracti1ity for hours in an
oxygenated environment.
3. If the concentrations of ions are abnormal,
then the heart will what happen?
1). If concentration of these ions is
altered then heart rate and
contractility 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 stop
heart during diastole .
2).An excess of sodium ions
depresses cardiac function like
potassium 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 heart
muscle .
3).Excess calcium ions in the fluids
enhance myocardial contractility .
When large amount of calcium
ions are infused into the
experimental animals, the heart
relaxes less during diastole and
eventually stops in systole
(calcium rigor). A deficiency of
calcium ions causes cardiac
flaccidity.
Drugs
1.The intrinsic properties of the
heart are inf1uenced by
autonomic nervous system.
Sympathetic and parasympathetic
nerve
2.Various drugs acting on specific
receptors present in the heart also
influence the cardiac activity.
• Acetylcholine(Ach) acts on
the M- receptors present in the
heart and causes the decrease
in the heart rate and cardiac
contractility.
• Adrenalin (Adr) acts on alpha
and beta-adrenergic receptors.
It has positive chronotropic
(increased heart rate) and
positive inotropic (increased
force of contraction)effects .
PROCEDURE
1.Expose the frog’s heart
• As compared to human heart, in the
frog’s heart, there are five chambers
ie one ventricle, two atrium, one
sinus venosus ,one truncus arteriosus
• There is no special conducting tissue.
• There is no coronary circulation in
the frog’s heart
Truncus arteriosus
ventricle
atrium
ventricle
sinus venosus
• 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.
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 atrioventricular 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 and
finally the truncus arteries.
If we remove the heart from the animal’s body and
immerse it in Ringer solution placed, the various parts of
the heart are seen to continue to beat in the usual regular
sequence. This indicates that the heartbeat originates
from the heart itself.
PROCEDURE
2. Connect the heart clip with the
apex of the ventricle. Lift the heart
gently by raising the lever and
adjust its position so that the
beating heart produces good
movements. Pour Ringer solution
on the heart from time to time .
3. Adjust the velocity and
sensitivity ,record normal curve.
PROCEDURE
• 4. Pour 0.65% NaCl
solution(deficiency of calcium ) on
the frog’s heart and record its
effect on the cardiac activity.
• 5. 1%KCl solution
• 6. 1%CaCl2 solution
• 7.1/10000 acetylcholine solution
• 8. 1/10000adrenalin solution