Download NAMES ___ . DATE __ _ CARDIAC CYCLE OF THE FROG

NAMES _ _ _.
DATE _ __
CARDIAC CYCLE OF THE FROG
PREPARATION: Know the answers to the following questions:
What is systole? diastole? In which direction does blood flow in the frog heart?
How does the blood leaving the lungs differ from that arriving?
Remember, the frog's heart has only one ventricle into which both the right and
left atria discharge their blood.
MATERIALS: Dissecting pan lined with moist paper toweling, thread, S-shaped pin hook,
blunt probes, soc and 3ooc water baths, urethane anesthetic, frog or toad
Anesthetize the frog with 1 mi. or urethane anesthetic per 100 g body weight into the dorsal
lymph sac. Let animal wait about 20 minutes before starting surgery. Check for alertness
by turning frog onto its back or touching its cornea for lack of a reflex blink.
Fasten the frog dorsal side down in the dissecting pan with pins through the wrists and
ankles. Lift up the skin over the ventral side of the abdomen and with scissors, slit the skin
from the lower abdomen up to the jaw. Next, make a longitudinal cut through the body
wall, keeping a little to one side of the midline to avoid cutting the large abdominal
vein.
Cut through the shoulder girdle. There is a reflex action of the frog adducting its arms when
the cut is made, but it doesn't mean that the frog is awake. Pull the forelegs well apart and
secure in this position with the pins. Try to cut the pectoral area open without cutting open
the pericardium. You may need to cut away the sternum and surrounding tissue to expose
the heart well.
Observe and answer numbered questions as you go along:
a) the pericardium: notice carefully the size of the heart in dilation. With a corner of a
piece of paper towel, wipe up any blood that may have accumulated . Notice the thinness,
strength, and inelasticity of the pericardium.
Slit open the pericardium without letting any blood into the sac. Pass the tip of
your finger gently over the heart and note the moisture on the surface of the heart.
1. When the pericardium has been well removed, note the size of the dilated heart. Did it
change size at all?_ _ _ _ _ _ _ _ _ _ _ _ __
2. What are the two functions of the pericardium did you just observe before and after
cutting open the perricardium?_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
Now apply Ringer's solution to keep the exposed heart moist.
b) Observe the two atria-3. Any difference in color between the right and left atria? Explain :_ _ _ _ __
c) Observe the ventricle as it beats.
4. Contrast its wall with that of the atria and explain:_ _ _ _ _ _ _ _ _ _ __
d) Observe the conus arteriosus--the vessel coming from the ventricle and dividing into
two aortae--one branch going to the body and the other dividing to go to the lungs.
e) On the dorsal side of the heart is the sinus venosus. To see it, you will need to lift up
the heart gently with the forceps and look at the dorsal side. The sinus is a very thin walled
sac in a triangular shape.
f) Draw the direction of blood flow in the frog heart and label the parts-abbreviations fine :
g) Notice the sequence of contraction of the parts in the following order--atria, ventricles, and
conus arteriosus. Determine the rate per minute (if the beat is regular, just count for 15 sec.
and convert to minutes.--all rates should be on a one minute rate
5. Normal rate per minute: _ _ _ _ _ __
6. Is the rate of the atria the same as that of the ventricle?_ _ _ _ __
7. Compare the rate of the right and left atria--same? _ _ _ _ _ __
8. What kind of blood is in the ventricle?_ _ _ _ _ __
9. How is the mammalian heart superior to the frog's heart in that respect?_ _ __
h) Notice the changes in the shape, size, and position of the ventricle during its systole and
diastole. Particularly notice the play of colors.
10. If the ventricle contracts and relaxes without this change in color, what may you
conclude?_ _ _ __ _ _ _ _ __
i) The pacemaker, the sinus venosus: put as-shaped hook barely into the apex of the
ventricle--just catch the muscular wall--do not puncture the ventricle chamber itself!!
Loop the tie around a T -pin just anterior to the head and lift the ventricle forward and
upward--pull just enough to lift the heart up to expose the sinus venosus.
Take 2-3 cooled (in ice bath at about soc) rods. Put the blunt end of the cooled rod on
the sinus and then start counting the ventricle for 1S seconds--you may change cool rods
half way to insure chilling.
Let the heart come back to normal before going to the next temperature test.
j) Repeat but apply the cooled rod to the ventricle only. Again count for 1S seconds.
k) Repeat i and j except use the warmed rod--3soc. Record your results in the table
below.
11 . Normal Heart Rate: _ _ _ __ _
soc Rod
3soc Rod
12. Rod on Sinus
Ventricle
AUTOMATICITY OF THE HEART
I) Remove the heart by cutting through arteries and veins--be sure to take the sinus
venosus. Place the heart in a small culture dish of Ringer's solution.
13. Count the rate once it resumes a regular beat. _ _ _ _ _ _ _ __
14. What have you proved as to the relation of the heart beating and the central nervous
system? _ __________________________
m) With scissors, carefully cut off the sinus from the rest of the heart.
1S. What is the rate of the heart now?_ _ _ __ _ Rate of the sinus?_ _ __
n) Now cut the atria apart from the ventricle-16. Rate of atria: _ _ _ ___ Rate of ventricle:________