The Importance of Animal Physiology

The Importance of  Animal Physiology

Why is the study of animal physiology important to you and to people in general? Not the least of the reasons is the one we have already emphasized—namely, that a full understanding and appreciation of all the marvels and other phenomena of the animal world depends on an analysis of how animals work. The study of physiology draws us beyond surface impressions into the inner workings of animals, and nearly always this venture is not only a voyage of discovery, but also one of revelation. The study of physiology also has enormous practical applications because physiology is a principal discipline in the understanding of health and disease. The analysis of many human diseases—ranging from aching joints to heart failure—depends on understanding how the “human machine” works. A physician who studies heart disease, for instance, needs to know the forces that make blood flow into the heart chambers between one heartbeat and the next. The physician also needs to know how pressures are developed to eject blood into the arteries, how the cells of the heart muscle coordinate their contractions, and how the nutrient and O2 needs of all parts of the heart muscle are met. We discuss these and other aspects of mammalian physiology extensively in this book. Even when we turn our attention to other types of animals, our study will often have application to human questions. One reason is that nonhuman animals are often used as “models” for research that advances understanding of human physiology. Research on squids, for instance, has been indispensable for advancing knowledge of human neurophysiology because some of the nerve cells of squids are particularly large and therefore easily studied. Physiology is as important for understanding the health and disease of nonhuman animals as it is for understanding health and disease in humans. An example is provided by studies of another group of migrating animals, the Pacific salmon—which swim up rivers to reach their spawning grounds . Physiologists have measured the costs these fish incur to swim upstream and leap waterfalls. This research has enabled better understanding of threats to their health. For instance, although each individual dam along a river might be designed to let salmon pass, a series of dams might so increase the overall cost of migration that the fish—which don’t eat and live just on their stores of energy when migrating— could run out of energy before reaching spawning grounds. With knowledge of the energetics of swimming and leaping, managers can make rational predictions of the cumulative effects of dams, rather than simply altering rivers and waiting to see what happens. The effects of water pollutants, such as heavy metals and pesticides, are other important topics in salmon physiology. Examples in other animals include studies of stress and nutrition. Conservation biologists gauge the stress experienced by wild vertebrate animals by measuring levels of stress-response hormones in their blood .

Careful studies of nutrition have solved mysterious cases of population decline by revealing that the animals were unable to find adequate amounts of acceptable foods. In brief, physiology is one of the key disciplines for understanding  The fundamental biology of all animals  Human health and disease  The health and disease of nonhuman animals of importance in human affairs Physiology is also important because it is one of biology’s most integrative disciplines. Physiologists study all the levels of organization of the animal body. In this respect, they are much like detectives who follow leads wherever the leads take them. To understand how an organ works, for instance, information about the nervous and hormonal controls of the organ might be required, plus information about enzyme function in the organ, which might lead to studies of the activation of genes that code for enzyme synthesis. Physiology not only pursues all these levels of biological organization within individual animals but also relates this knowledge to the ecology and evolutionary biology of the animals. Students often especially enjoy their study of physiology because the discipline is so integrative, bringing together and synthesizing many concepts that otherwise can seem independent. Consider again, for example, the Pacific salmon. As juveniles, these fish migrate from rivers to the open ocean. Years later, they return to the very rivers of their conception to procreate the next generation. Before a returning salmon enters freshwater, it maintains its blood more dilute than the seawater in which it swims. After it enters freshwater, however, it must maintain its blood more concentrated than the dilute freshwater now surrounding it. Another challenge the salmon faces is meeting the energy costs of its migration. Once in its natal river, a salmon no longer eats. Yet it may swim for many weeks before it reaches its spawning grounds—sometimes traveling against the river current as far as 1100 km (680 mi) and, in mountainous regions, climbing 1.2 km (0.75 mi) in altitude. During this trip, because the fish is starving, it gradually breaks down the substance of its body to supply its energy needs; 50–70% of all tissues that can supply energy are typically used by the time the fish reaches its destination. 

As physiologists study salmon, they take a highly integrative approach, . As part of their background of knowledge, they recognize that the populations and species of salmon alive today not only are products of evolution but also are still evolving . Physiologists also recognize that the laws of chemistry and physics need to be considered , because animals must obey those laws—and sometimes they exploit them. For understanding swimming, multiple levels of organization must be considered . The nervous system generates coordinated nerve impulses that travel to the swimming muscles, which contract using energy drawn from adenosine triphosphate (ATP) that is synthesized from organic food molecules. The contraction of the swimming muscles then exerts biomechanical forces on the water that propel the fish forward. The investigation of swimming illustrates, too, the important general point that the study of function typically goes hand in hand with the study of form; knowledge of anatomy often sets the stage for understanding physiology, and as function is clarified, it typically helps account for anatomy. Often, the ultimate goal of a physiological study is to understand how an animal functions in its natural environment. Thus, an ecological perspective is vital as well. when an individual salmon’s fluid environment changes from saltwater to freshwater, the fish alters the set of ion-transporting proteins expressed in its gills, permitting inward ion pumping in freshwater whereas ions were pumped outward in saltwater. The distance a fish swims is another important ecological consideration. Different populations of salmon travel vastly different distances. Going far upriver can provide advantages of certain kinds, such as providing pristine spawning grounds. However, this ecological factor has other consequences as well. Females that exert great effort to reach their spawning grounds, such as by swimming great distances, spawn fewer eggs because swimming diverts energy away from use in reproduction