Observational experiments on the pacing point of cardiac activity in the toad, Bufo vulgaris
Observational experiments on the pacing point of cardiac activity in the toad, Bufo vulgaris
This experimental method was obtained from the official website of the Fourth Military Medical University
Operation method
Observational experiments on the pacing point of cardiac activity in the toad, Bufo vulgaris
Principle
The special conduction system of the heart has autorhythmicity, but the autorhythmicity of each part is different, with the highest autorhythmicity in the venous sinus of amphibians (and the highest autorhythmicity in the sinus node of mammals). Each excitation of the normal heart starts from the part with the highest autoregulation and passes to the atria and ventricles in turn, successively causing atrial and ventricular contractions. The site of highest autoregulation is called the pacemaker of the heart. When the normal autoregulation is affected and changed, the activity of the atria and ventricles also changes accordingly; if the downward transmission of excitement from the pacemaker is blocked, the activity of the lower part of the heart will temporarily stop, or even show its own autoregulation. In this experiment, the frequency of the activities of the various parts of the heart (the number of activities in one minute) is used as an indicator, and the local temperature of the surface structure of the heart is changed, combined with the use of ligature, to observe the effect on the auto-rhythmic activities in different parts of the heart, to understand the auto-rhythmicity of the different parts of the frog's heart, and to analyze the parts of the frog's heart that are at the point of pacing.
Materials and Instruments
Frogs Toads Move I. Separating the heart Caveat 1. Do not make too large an incision to avoid injury to blood vessels. Be careful when cutting the pericardium to avoid injury to the heart. 2. the ligation site should be accurate, do not ligate the venous sinus. 3. keep the exposed tissues moist by adding drops of Ren's solution during the experiment. 4. Each experiment should be performed after the cardiac activity has stabilized after the previous experiment. For more product details, please visit Aladdin Scientific website.
Ren's solution Warm water and ice Commonly used frog surgical instruments Frog plate Frog leg retaining clips Frog heart clip Stopwatch Drip tube Silk wire
1. Expose the heart
A toad was taken, and the brain and spinal cord were destroyed with a frog needle through the foramen magnum of the occipital bone, and then fixed dorsally on a frog plate. With the left hand, lift the skin at the lower end of the sternal raphe with a pair of toothed forceps and make a small incision with surgical scissors. Then insert the scissors into the subcutaneous area from the incision, and cut the skin in the direction of the clavicle on the left and right sides. The skin was lifted to the cephalic end, and then the abdominal muscle at the lower end of the sternal raphe was lifted with toothed forceps, and a bite was cut in the abdominal muscle, and the scissors were inserted into the thoracic cavity (do not injure the heart and blood vessels), and the thoracic wall was cut along the direction of the skin incision, and the right and left rostral and clavicular bones were clipped, so that the incision was in the shape of an inverted triangle. The pericardium was lifted with ophthalmic forceps, and the heart was exposed by carefully cutting the pericardium with ophthalmic scissors. The structure of the heart is shown in Figure 1.
2. Observation of the external structure of the heart
The atria, ventricles and atrioventricular groove can be seen from the ventral surface of the heart. In the upper right part of the ventricle there is an enlargement at the root of the artery, called the arterial cone. The trunk of the artery emanates from this and divides upward into right and left branches. Turning the heart cephalad with a glass minute needle reveals a rhythmically pulsating venous sinus at the inferior end of the atrium. Between the atria and the venous sinus is a white half-moon shaped boundary called the sinusoidal groove.
II. Observation Items
1. Observe the course of the heartbeat Carefully observe and record the frequency, sequence and interrelationship of the venous sinus, atrial and ventricular contractions.
2. Touch the bottom of a small test tube containing 37℃ hot water or 4℃ cold water to the venous sinus in order to change the local temperature, and observe and record the changes of the heart beating activities.
3. Remove the test tube and wait for the heartbeat to return to normal, from the ventral surface with ophthalmic forceps in the aortic trunk below a line, turn the heart to the head end, and accurately in the sinusoidal groove to make a ligation, blocking the conduction between the venous sinus and the atrium, known as Sclerotinia first ligation. Observe and record the changes in the rhythm of activity of each part of the heart and the number of beats per minute. After the atria and ventricles have resumed beating, count the frequency of their beats separately.
4. Thread a wire through the atrioventricular junction to accurately ligate the atrioventricular groove, known as the second ligature of the sigmoid. After the ventricles have resumed beating, record the number of beats per minute of each part of the heart, and observe the pattern of activity of each part and its relationship to each other.
5. Fill in the following table with the results of the above recordings.