Transcript Physiological Properties Of Heart Muscle Frog Dissection

Physiological Properties Of
Heart Muscle
Frog Dissection
Background
Frog’s myocardiogram gives the medical students a
clear understanding of the normal sequence of atrial
and ventricular contraction and the effect of
temperature, sympathetic stimulation and
parasympathetic stimulation on frog’s heart.
The Frog Heart And Circulation
The frog heart has 3 chambers:
two atria ( Rt and Lt) and a single ventricle.
The Rt atrium receives deoxygenated blood from
the blood vessels (veins) that drain the various
organs of the body.
 The Lt atrium receives oxygenated blood from the
lungs and skin
 Both atria empty into the single ventricle.
While this might appear to waste the opportunity
to keep oxygenated and deoxygenated bloods
separate, the ventricle is divided into narrow
chambers that reduce the mixing of the two blood
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So when the ventricle contracts oxygenated
blood from the left atrium is sent, relatively
pure, into the carotid arteries taking blood to
the head (and brain)
Deoxygenated blood from the right atrium
is sent, relatively pure, to the pulmocutaneous
arteries taking blood to the skin and lungs
where fresh oxygen can be picked up.
Only the blood passing into the aortic arches
has been thoroughly mixed, but even so it
contains enough oxygen to supply the needs
of the rest of the body
Frog Heart
Frog Circulation
Physiology Of Heart
The heart's primary function is simply to act
as a pump that provides pressure to move
blood to its ultimate destination.
Cardiac muscle differs from skeletal muscle
both morphologically and functionally. It is
able to initiate its own rhythmic
contractions without requiring a stimulation
from outside the heart. This is due to "leaky"
cell membranes, in which calcium and
sodium ions slowly leak into the cells. This
leaking causes a slow depolarization to
threshold, thus firing an action potential and
initiating contractions of cardiac muscle
The cells that are most leaky to ions
and that depolarize fastest , control the rate
of contraction of all other cardiac cells; thus,
they act as pacemakers for the rest of the
heart. In the mammalian heart, the pacemaker
is the sinoatrial (SA) node.
In the frog heart, the pacemaker is the
sinus venosus, an enlarged region between the
vena cava and the right atrium, that receives
blood from the anterior and posterior caval
veins and empties blood into the right atrium.
Equipments
Frog
 Dissection set
 Kymograph
 Frog Ringer solutions
 Pins
 Droppers
 Suture thread
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Composition of frog ringer solution
Ringer’s solution, composed of:
– NaCl: 200 ml
– KCl: 20 ml
– MgCl2: 20 ml
– CaCl2: 4 ml
– NaOH: 25.8 ml
– Glucose: 1.8 g
– pH: 7.4
– Distilled water: to make 2 L
– Total Volume: 2 L.
Frog Preparation And Dissection
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Prepare the frog for dissection by PITHING the frog
Fix the frog on its back using the big needles
Open the thorax of the frog with a central incision and
two flaps
Hold the pericardium with forceps and carefully cut away
the sac from the heart, using scissors
Do not cut or remove any organs other than the skin and
some of the ribs covering the heart
Keep the heart ,moist during the procedure by putting
drops of ringer lactate by syringe
Cont…
Attach a clip to frogs heart and by thread
connect it to your kymograph machine.
 Now start your experiment.
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A- Heart Beat
Identify the part of the heart and examine its beating
 Measure the normal heart rate
 Using single stimuli of 100mV and 1-msec duration,
stimulate the ventricle at different times in the cardiac
cycle, and note the following
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 What
is the result of stimulating during the
systolic phase of the cycle?
 What is the result of stimulating during the
diastolic phase of the cycle?
 Can a second contraction be elicited before
the normal rhythmic contraction occurs
B- Temperature effect
Record the heart contractions at room
temperature.
 Drop warm (40oC) frog Ringer's solution on
the heart until significant changes are seen
in rate and contractility.
 Drop cold (5oC)) Ringer's on the heart and
record when changes are observed. Then
rinse the heart with room-temperature
Ringer's to return the beat to normal before
continuing the
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Temperature is always a controlling factor for
chemical reactions.
the heart beat is a function of chemical processes. Ca2+
protein interaction brings about the contractile event
and is a chemical reaction using ATP as the energy
source to drive each contraction.
A chemical reaction approximately doubles its rate
every time you increase the temperature 10 degrees
centigrade, and approximately halves its rate every time
you decrease the temperature 10 degrees centigrade.
THE COOLER THE SLOW
THE WARMER THE FAST
C- Drug effect (NEUROTANSMITTERS)
Using a syringe apply the following drugs to the heart
until you see significant changes in rate, contractility,
or tone.
Acetylcholine 0.1 mg/ml in Normal Frog Ringer
Atropine 1 mg/ml in Normal Frog Ringer
Epinephrine 1mg/ml in Normal Frog Ringer
 Note:
Best results are seen if the drug is dropped on the sinus
venosus.
After the effect is recorded, rinse the heart with frog
Ringer's and allow the heart to return to normal before
the next drug is applied.
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D- Propagation Heart Block
Using a heavy thread, tie a loose single-loop ligature around the
heart at the junction of the atria and ventricle.
 Note the following type of heart block:
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First-degree block. The interval between atrial and
ventricular contraction is prolonged.
• Second-degree block. Some impulses fail to reach the
ventricle so that the ratio of atrial to ventricular beats
is altered. You may see 2:1, 3:1, 5:1, 8:1 types of heart
block.
• Third-degree block. Impulses fail to pass through the
AV node and bundle of His and the ventricle may
start its own independent rhythm of beating, or you
may see only the atria contracting.
After producing a complete heart block (third degree),
release the ligature , and see if a normal AV beat is
restored.
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