This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
Biology 202, Spring 2005
Third Web Papers
Out of all the living creatures on Earth, humans are the only species choosing to bear the responsibility of caring for other species, which we have been doing for over ten thousand years. The domestication of canines began around 9000 BC (2). Humans observed their hunting abilities and used the dogs as an aid for their own survival. Not only did the dogs provide humans with sustenance, but they also offered a form of protection, which is probably how they were discovered to be such loyal companions (2). Cats have also been living in the vicinity of humans for thousands of years. The Ancient Egyptians were known to keep cats for rodent control purposes, as well as worshiping them as deities(3) . Ancient art also depicts man and dog, side by side, which can attest to the value we have given them throughout time.
While pets clearly benefit humans by supplying ample camaraderie, recent studies have shown them to positively effect our cardiovascular and autonomic nervous systems too. Before looking at various studies, we must first understand the anatomical structures pets are claimed to influence. The autonomic nervous system consists of the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The sympathetic nerves run along side the vertebral column and branch off into organs (including skin tissue), glands, and other ganglia. The SNS and PNS regulate internal body functions and are usually not controlled by the I-function (they are involuntary). When the SNS is activated, the preganglionic neurons (neurons that bring signals from the central nervous system to ganglion) release the neurotransmitter acetylcholine, which stimulates action potentials in the postganglionic neurons. The postganglionic neuron then projects to the "target" organ and at its synapse it emits noradrenaline, or norepinephrine (4). These neurotransmitters act predominantly on the alpha receptors; when noradrenaline is received on capillaries and blood vessels, for example, the alpha receptors cause vasoconstriction. The release of noradrenaline makes the heart pump faster, thus causing blood pressure to rise, widens bronchial passages, and dilates our pupils(4) . The PNS has the opposite physiological effects of the SNS, namely bringing the body back to a resting state(4) .
One study, done at an assisted living center in Illinois, examined the effects of dogs on human vital signs (heart rate, blood pressure, and oxygen saturation) (5). The subjects consisted of fifteen women, all between the ages of 76 and 90, and the dogs were "non-bonded" to the women (they didn't have any prior contact with the pets). The experiment began by recording the women's blood pressure, heart rate, and oxygen saturation. Then two dogs were brought into the room and the subjects touched and held them. After ten minutes, the women's vitals were taken again, and the dogs were removed from the room. The women were instructed to sit quietly for five more minutes, after which a third reading was done. The results showed that 13 out of 14 subjects' blood pressure decreased (the fifteenth subject could not be read), and the subjects' heart rate revealed a significant decreasing trend as well. Changes in oxygen saturation, however, were not noteworthy(5) . These researchers concluded that dogs may have a beneficial effect on elderly women's cardiovascular system, and this experiment indicates that the parasympathetic nervous system response can be boosted by interaction with a friendly animal.
Another group of researchers, at State University of New York at Buffalo, wanted to demonstrate that owning a pet can have calming effects on the body when it is reacting to psychological stress (6). They conducted an experiment on 48 stockbrokers (men and women), all of whom had no other conditions than hypertension and had not owned a pet at any point in the past 5 years. All of the subjects were prescribed an antihypertensive drug, called Lisinopril, and were split into two groups. One group was the control group and went home with just the standard drug therapy, and the other group was given both drug therapy and a dog or cat (7). Before beginning either type of therapy, both groups had similar responses to the "stress tests" the researchers performed on them. Six months later the tests were done again, and while the drug therapy lowered each groups' blood pressure, the people with pets had a noticeably lower response to mental stress than the control group(6) . When told about the results many of the control group subjects even went out and bought a pet (8). One of the experimenters said that the findings suggested that when a person with high blood pressure is under stress, owning a pet can really help, especially if the person has a "limited support system" (8) . On a neurobiological level, pets can help reduce stimulation of the SNS, which is commonly caused by stress, thus controlling blood pressure.
Aside from stress relief, pets can aid humans psychologically in a number of other ways too. For many people, children especially, keeping a pet can improve one's self–esteem (9). It is not that difficult to make your dog or cat happy, all you have to do is play with it or pet it; basically they just want to be loved like humans do. However, humans are harder to please and generally we are not that quick to forgive and forget. Pets, on the other hand, do not pass judgments and if you care for them, they repay you with unconditional love, which makes people feel needed. Owning a pet also teaches children responsibility, because they require a great deal of care and attention (9). Many people find their pets to be a great conversation starter too, as it is something numerous people have in common with one another.
Ultimately, it seems as though the benefits of pet ownership outweigh the majority of disadvantages (of course there are exceptions, such as allergies). In particular, there appears to be sufficient proof that pets can alleviate stress, and of all the places in the world that cause mass amounts of stress are college campuses. Massachusetts Institute of Technology (MIT) recognized this, and five years ago they began allowing select residence halls to have a limited number of cats(10) . Not only do the students say the offer companionship and stress relief, but they also control the number of mice, which seem to be a growing problem at Bryn Mawr. The pros of pet owning still need to be explored, but they are clearly not detrimental; it is only a matter of time until various institutions (colleges, nursing homes, etc.) are aware of calming they can be, and permit them.
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