Chapter 49-Homeostasis

Chapter 49-Homeostasis - Chapter 49 Maintaining the...

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Chapter 49 – Maintaining the Internal Environment – HOMEOSTASIS Much of this chapter has been covered in the other chapters to one degree or another. However, several topics remain: disposal of nitrogen, balancing body heat, evolution of the vertebrate kidney, and osmoregulation. All of these topics are important to your education as young science students. As always, the Concept Outline and the Chapter Review Outline provide excellent places to begin your preparation in understanding this material. Homeostasis is defined on P. 1040. Basically, the body operates at an optimal level within very narrow ranges of physiological tolerance. There is an optimal “set point” for each physiological function. For example, there is an optimal body temperature, blood pH, blood protein concentration, blood nitrogen level, blood glucose level, blood oxygen level, hydration, and so forth. The body cannot maintain these set points in absolute terms, i.e. the temperature of the body is going to change with activity, exposure to sun (or lack of sun), changes in air or water temperature. When the physiological state of any condition begins to change, the body begins to initiate activity to bring the physiological state back to “normal.” This is homeostasis , as I understand it. Regulatory Mechanisms: Negative Feedback Loops – Fig. 49.2; 49.3. Stimulus moves physiological condition from normal ‘set point.’ Sensor picks up the change, measures the deviation. CNS communicates with effector to moderate condition so that physiological state returns to normal. Figs.49.5 and 47.19 are good exampled. Blood glucose levels go up, set point is violated, insulin is secreted, blood glucose levels go down, original set point achieved, no more insulin is secreted. Positive Feedback Loops – Positive feedback loops are uncommon because the feedback system tends to move the set point farther from the normal state. Two examples are often given: childbirth (Fig. 49.7, and orgasm in the sex act. Antagonistic Reactions – Fig. 49.6 describes a nonbiological example of antagonistic reactions. A biological example can be seen in Fig. 47.19. In this case, consider glucagon. Glucose levels rise, the set point is violated, insulin is secreted, glucose levels fall, no more insulin; BUT if glucose is need, glucagon is secreted, glucose levels rise – maybe too high, glucagon shuts off, but insulin is secreted. So one molecule is antagonistic to the other. Feedforward – this term is not in your textbook, but it describes the body’s anticipation to a certain condition and the physiological adjustments to deal with the condition. Osmolality: Most of this chapter deals with water balance between the intracellular and extracellular environments (Fig. 49.8). There is a difference between
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This note was uploaded on 03/31/2008 for the course BIOL 1106 taught by Professor Georgesimmons during the Spring '08 term at Virginia Tech.

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Chapter 49-Homeostasis - Chapter 49 Maintaining the...

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