Frog Heart Lab, Animal Physiology

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Chemical and Environmental Effects on the Heart
Introduction
The heart is the centerpiece of the circulatory system, its muscular contractions allow for the timely delivery of essential gases and nutrients to virtually all cells of the body. The pressure created by the heart also plays a vital role in eliminating wastes through organs such as the kidney, thus the heart delivers and helps maintain nutrient and waste composition throughout the body. The heart, like all muscle cells, releases ionic calcium when stimulated which binds to troponin which in turn causes tropomyosin to uncover the myosin-actin binding sites on the muscle. Temperature has effects on the metabolism and activity of all cells. Warmer temperatures increase the kinetic energy of molecules in cells, providing more energy which allows metabolic processes to proceed more quickly. Cooler temperatures, on the other hand, decrease molecular kinetic energy and cause slower metabolic rates in cells and tissues, hence when a bear hibernates, its body temperature is some degree lower than it is during the bear’s active periods. The heart is also susceptible to certain molecules for which are able to bind to its receptors or diffuse across its membrane and affect intracellular activity and consequently have effects on the overall homeostatic condition of the organism. The Sinoatrial Node (SA Node) acts as the pacemaker of the heart by providing a small, autorhythmic electrical pulses that travel to the atrioventriclar node (AV node) and through the Bundle of His and Purkinje Fibers through gap junctions at the intercalated disks which stimulate the cells of the heart to contract via calcium release. This contraction is similar to a neuron in the sense that a threshold stimulus is needed to cause a contraction, a refractory period follows contraction at which time a new contraction cannot occur. Drugs that have an effect on the tissues of the heart, especially those where the SA Node resides can have an effect on the frequency and strength of muscular contraction via causing a stimulus to occur and lowering the threshold needed to cause a contraction. The heart is under both nervous and hormonal control. The brain is constantly receiving information from the body such as pH, CO2 levels, and many others that the hypothalamus and medulla play a role in translating and reacting to via the release of hormones such as epinephrine which affects the SA node, either by stimulating or inhibiting contraction rate. Removal of the heart from the body would result in eventual cessation of beating as these sources are depleted from the immediate environment, not to mention the absence of the appropriate ion levels needed to maintain resting cellular electrochemical gradients. All of the aforementioned aspects of heart control coordinate with Starling’s Law of the Heart, which relates to stroke volume, contractions strength, and frequency of heart contraction. This paper is interested in investigating what the effects of the alteration of temperature, chemical environments, and physical obtrusion have upon the strength and frequency of cardiac muscle contractions. Decreasing the temperature of the heart’s environment should hypothetically result in a decrease in both frequency and strength of contractions due to the decreased ability of calcium ion channels to open and cause contraction. Various chemicals such as epinephrine and calcium ion solutions should correlate to both and increase in frequency and strength of the resultant contractions due to direct effects on the hearts mode of activation (SA node stimulus) and increasing the levels of available calcium needed to cause a contraction. Other chemicals such as Atropine should indirectly increase heart rate via the blocking of the effects of the parasympathetic system resulting in a predomination of sympathetic activity. Acetylcholine, which acts on the muscarinic receptors of the heart, should display...
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