Introduction: Our bodies need to be in balance in order to function properly, and there are many ways the body maintains balance, or homeostasis. Homeostasis is the maintenance of nearly constant conditions in the internal environment. Our normal heart rate is an example of our body in homeostasis and any sort of change, or stimulus, can alter it. Exercise, adrenaline in the blood, and a low blood pH are all stimuli that increase the heart rate. Exercise, for example, stimulates stretch receptors in the muscles. These receptors then send a signal to a part of the brain called the medulla oblongata that receives the sensory input. It then in turn sends nerve impulses to the sinoatrial node in the heart. This node generates an impulse and initiates contraction of the heart at a quicker pace. Thus, the heart beats faster, which equals an increased heart rate. This is an example of a homeostasis imbalance. The heart reaches homeostasis again when exercise ceases and the heart rate drops down to its basal rate, or its rate at rest. This whole process is an example of a negative feedback cycle: a stimulus (increased heart rate) sends receptors to the control center (medulla oblongata), which then sends effectors (impulses by the vagus nerve, or the efferent pathway) to the heart to slow the heart contractions, thus reducing the heart rate and bringing it back to its basal rate.
In our experiment we studied heart rate before and after a brief exercise session. Our hypothesis is exercise will increase the heart rate, and a negative feedback mechanism will occur to restore the heart rate back to its normal basal rate. Materials: Stop watch, metronome, stairs
•Eight subjects took their own resting, or basal, heart rate for 15 seconds while standing up. Some subjects chose to take their heart rate at their carotid artery, and some took their pulse using their radial artery. This number was multiplied by 4 to get beats per minute. This is how all heart rate measurements were taken throughout the experiment. •Subjects did exercise session. They walked down 57 stairs and then back up those same 57 stairs for a total of 104 stair steps. This was done at a pace of 85 beats
per minute. The whole session took 1 minute 45 seconds. •Subjects immediately took their heart rate after they completed the exercise. •After 1 minute of completing the exercise, subjects measured their heart rate again. This was done at 1 minute intervals for a total of 5 heart rate measurements after completing the exercise. •All together, subjects took 6 heart rate measurements: 1 before the exercise, and then 5 after the exercise. Data/Results: See attached graph and table.
Conclusion/Discussion: The data shows that heart rate increases during and after exercise and begins to drop back down close to the basal rate after rest. The heart progressively decreases after each minute of rest. Our results show a negative feedback mechanism was used to control the heart rate after exercise. The increased heart rate stimulated the medulla oblongata which sent impulses to the sinoatrial node of the heart to slow down contractions and decrease the heart rate. Different subjects had differences in the time it took for their heart rate to drop after the exercise, but heart rate decreased nonetheless. Overall, our hypothesis was shown to be correct from the experiment. We chose the heart rate as our variable because it is easy to measure and gives clear results. We predicted that the heart would increase after a brief exercise session, and our results matched that prediction. As for other experiments, we could perform different activities or tasks and measure our heart rate after those. We could even hold a serious/heated discussion and see if heart rate is affected in an intense conversation. There are many different things you could do to test heart rate, as exercise is just one example.
Data: Each subject and their heart rate at certain time interval: SubjectBefore exercise0 minutes rest1 min. rest2 min. rest3 min. rest4 min. rest 1100 BPM120 BPM104 BPM104 BPM104 BPM104 BPM
Summary statement: Heart rate increases during and after exercise and begins to drop back down close to the basal rate after rest.
Heart Rate Regulation in Humans. (2010, January 23). The Student Room. Retrieved August 24, 2013, from http://www.thestudentroom.co.uk/showthread.php%3Ft%3D1059551%26page%3D45&q=&esrc=s&ei=EEIuUtiHKMKUiQL86YDQDQ&usg=AFQjCNGj9jN4mV3pDlB7dF1yuUm0gn81gA