Abstract
The functioning of the heart is affected by a number of factors. This paper presents a study in which the heart of a toad is used to study the functioning of the heart with a focus on the effects of temperature, drugs, and calcium concentration. The characteristic of the heart of a frog being myogenic is applied in conducting the experiment. It involves the use of MacLab apparatus to understand the impacts of these factors on the functions of the heart. This results in the conclusion regarding the topic thus providing insight on the impacts of variation of these factors on the functioning of the heart of a toad.
Introduction
Toads have a special heart feature of being myogenic. This is the ability of the heartbeat to function without the control of the nervous system. The contractions in the heart result from the excitement created by the cardiac muscle membranes which are subjected to depolarization until a particular threshold is reached when the action potential begins. This results in depolarization that ensures the whole process is repeated. The depolarization from the resting state to threshold potential takes place in the cells which constitute the ‘pacemaker’ which is located in the sinus venosus in toads. Despite the spontaneous beating of the heart, it is possible to control the rate and force of contraction. This has been achieved through stimulation of the sympathetic nerves that supply the heart that have an effect on the rate of heart contraction and increase in beat rate.
The adrenalin that is released from the nerve endings results in a decrease in the stability of the cell membranes contributing to their excitation. The functioning of the heart of a toad is facilitated by the availability of oxygen and nutrients which enable it to function correctly. As a result of this function, it has been used as the beast specimen for conducting scientific experiments aimed at understanding the functions of the heart and factors affecting the functions of the heart of poikilotherms. This is because toads are poikilotherms, hence their body temperatures are controlled by the surrounding temperature. When the surrounding temperature is high, their body temperature rises and the reverse is true.
These characteristics of the heart were used to study the mechanical properties of the heart following the treatment of the heart of a frog by physical and chemical methods. The apparatus used for this experiment was McLab which was set up initially for the experiment.
Materials and Methods
The study involved setting up the MacLab for the investigation of the toad heart. The software that runs the program for the MacLab process was set up. An isometric force transducer was used during the experiment to enable variation of resistance across the terminals as the current flow. This enabled the analog signal created to be converted into a digital signal that could be seen through a computer. The force transducer was calibrated. This involved attaching weights of known values to the hook of the force transducer and recording the resulting deflection on the computer screen.
In addition, various weights were used, and the main focus was to determine their amplitudes the settings of the calibration were done and values were inserted. A frog was dissected and the heart of the frog removed and a knot was made around the arterial trunks and the process was repeated to form a double knot. The heart was placed into the force recording apparatus and allowed to equilibrate for 5 minutes and the load was increased on the heart by stretching the ventricle. A graph of amplitude of force against change in length was made.
The second experiment involved varying the concentration of external calcium in the organ bath and observing the variations of the force produced by the heart. The heart was re-equilibrated under initial conditions and a ringer solution of 5-10% force load and concentration of calcium was reduced until zero. A plot was made for Force (mg wt) against Calcium in the ringer and observations were made.
The third experiment involved a study of the effects of drugs on the heart by adding a few drops of the drug to the heart and observing the change in force produced.
The fourth experiment involved determining the effect of temperature on the heart. This was achieved by varying the temperature of the Ringer solution beginning with the room temperature. A higher temperature was used and changes in heart rate and force were observed. The experiment was repeated with a cold Ringer at 4oC and a decrease in force and heart rate was noted. A table was drawn illustrating the heart rate and force (mg wt) for each temperature involved in the experiment and a change in cardiac output was determined.
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Results
It was observed that when the concentration of calcium was zero, the heart rate was 0.084mV, for 1mMol concentration, the reading was 0.075mV, for 2mMol the reading was 0.0656mV, for 7.5mMol Concentration, the value was 0.0938mV and for 10mMol the reading was 0.0875mV.
It was also found that when the temperature was maintained at 4oC, the reading was 0.0938mV and when the temperature was raised to 20oC, the reading was 0.1125mV. This shows that the higher the temperature, the higher the heart rate.
When various drugs were used, a variation of reading values was obtained. For instance, when adrenalin was used, the reading was 0.0781mV, noradrenaline 0.0781mV, acetylcholine 0.0688mV, atropine 0.0625mV and acetylcholine 2nd 0.0719.
Discussion
Calcium is regarded as an important mineral during the facilitation of systolic heart movements due to its contribution to cardiac muscle contraction. During each heartbeat, the concentration of calcium in the systole of the heart is increased at least 10-fold from the resting level of the heart function to the active level. Consequently, the increase in heartbeat in the experiment as a result of the concentration of calcium can be explained by this theory.
In addition, high-temperature results in activation of metabolic activities of the body which results in an increase in heart rate. This can be explained by the results of the experiment where it was observed that the heart rate of the specimen was high at higher temperatures and low at lower temperatures.
There are some drugs that enhance heart rate while other reduces heart rate. This is based on various impacts resulting from the introduction of the drug into the body. From the experiment, it can be concluded that acetylcholine 2nd results in increased activity of the heart while atropine results in a reduction in heart rate.
Reference list:
- Bijlani, R. L., & Manjunatha, S. (2011). Understanding medical physiology: A textbook for medical students. New Delhi: Jaypee Bros. Medical Publishers.
- Feder, M. E. (1992). Environmental physiology of the amphibians. Chicago u.a: Univ. of Chicago Press.
- Ghai, C. L. (2013). A textbook of practical physiology. New Delhi: Jaypee Bros. Medical Publishers.
- Rastogi, S. C. (2005). Experimental physiology. New Delhi: New Age International (P), Ltd.
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