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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

CHAPTER 40 PHYSIOLOGY, HOMEOSTASIS, AND TEMPERATURE REGULATION 40.1 Why Must Animals Regulate Their Internal Environments? - All animals need nutrients and oxygen and must eliminate carbon dioxide and other waste products of metabolism. Single-celled organisms meet all these needs by direct exchange with the external environment. An internal environment makes complex multi-cellular animals possible Internal Environment the physical and chemical characteristics of the extracellular fluids of the body. Individual cells get their nutrients from this extracellular fluid and dump their waste into it. A stable internal environment makes it possible for an animal to occupy habitats that would kill its cells if they were exposed to it directly. - As multi-cellular organisms evolved, cells became specialized for maintaining specific aspects of the internal environment. - The evolution of physiological systems to maintain different aspects of the internal environment made it possible for multi-cellular animals to become larger, thicker, more complex, and more adaptable to external environments that are very different from the internal environment. Homeostasis the maintenance of a steady state, such as a constant temperature or a stable social structure, by means of physiological or behavioral feedback responses. Essential feature of complex animals. If a physiological system fails to function properly, homeostasis is compromised, and as a result cells are damaged and can die. - To avoid loss of homeostasis, physiological systems must be controlled and regulated in response to changes in both the external and internal environments. Homeostasis requires physiological regulation - The activities of all physiological processes are controlled speeded up or slowed down by actions of the nervous and endocrine systems. - To regulate the internal environment, information is required. Set point in a regulatory system, the threshold sensitivity to the feedback stimulus. www.notesolution.comFeedback information information relevant to the rate of a process that can be used by a control system to regulate that process at a particular level. Error signal any difference between the set point and the feedback information when they are being compared. Suggests corrective actions. Effectors some components of physiological systems; they effect the changes n the internal environments. They are controlled systems because their activities are controlled by commands from regulatory systems. Regulatory Systems a system that uses feedback information to maintain a physiological function or parameter at an optimal level. They obtain, process, and integrate information, then issue commands to controlled systems. A sensor is an important component of any regulatory system. - It provides feedback information that is compared to the internal set point. Negative Feedback Information relevant to the rate of a process that can be used by a control system to return the outcome of that process to an optimal level. Most common use of sensory information in regulatory systems. It is a stabilizing influence in physiological systems. It tends to return a variable of the internal environment to the set point from which it deviated. Positive Feedback amplifies a response (i.e., increases the deviation from the set point). Not as common as negative feedback. Examples include the responses that empty body cavities, such as, urination, defecation, sneezing, and vomiting. Another example is sexual behavior. Feedforward Information information that can be used to alter the set point of a regulatory process. Anticipates changes in the internal environment before that change occurs. Physiological systems are made up of cells, tissues, and organs - Each physiological system is composed of discrete organs, such as the liver, heart, and kidneys that serve specific functions in the body. These organs are made up of tissues.
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