Laboratory report The effects of drugs on cardiac physiology The study of cardiovascular physiology has been divided into five distinct parts, all focused on the cardiovascular system . The first laboratory was the use of the electrocardiogram (ECG). This studied the electrical activities of the heart by placing electrodes on different parts of the skin. The result is a calibrated paper graph of these activities. These charts are useful in diagnosing heart diseases and heart abnormalities. In addition to natural cardiac abnormalities, there are those induced by chemical substances. The electrocardiogram is useful for showing how these chemicals adjust the electrical impulses they cause. The second part of this lab was a computer simulation program to illustrate the electrocardiogram of a frog using various medications in an isolated setting. The computer program entitled “Effects of Drugs on the Frog Heart” was used to define experimental conditions for specific drugs. The different medications used were calcium, digitalis, pilocarpine, atropine, potassium, epinephrine, caffeine and nicotine. Each of these medications caused a different EKG and beats per minute reading. The calcium-magnesium ratio affects “cell membrane permeability” (Fox). When calcium is placed directly on the heart, three physiological functions result. The strength of the heart increases while the heart rate decreases. It also causes the appearance of “ectopic pacemakers in the ventricles, producing abnormal rhythms” (Fox). The effect of digitalis on the heart is very similar to that of calcium. It inhibits the ATP-activated sodium-potassium pump which promotes the absorption of extracellular calcium by the heart. This in turn strengthens the contraction of the myocardium (Springhouse). Pilocarpine, for its part, acts by reducing the heart rate. It achieves this by aiding the release of acetylcholine from the vagus nerve. Atropine, on the other hand, blocks acetylcholine receptors, thereby decreasing heart rate. By placing potassium directly on the heart, its extracellular concentration increases, thereby decreasing resting potential. This brings the resting potential closer to threshold and weakens myocardial contractions. The action of epinephrine increases the force of contraction and heart rate. Caffeine is a stimulant that also increases contraction force and heart rate. It inhibits phosphodiesterase which breaks down cyclic AMP, causing cAMP levels to increase. Nicotine actively binds to nicotinic receptors, causing stimulation of the parasympathetic ganglia.