Chapter 31 Homeostasis and the Organization of the Animal Body Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc Chapter 31 At a Glance 31 1 Homeostasis How Do Animals Regulate Their Internal Environment 31 2 How Is the Animal Body Organized Biology Life on Earth 9e Copyright 2011 Pearson Education Inc Look at figure 31 2 Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment The cells of the animal body cannot survive if the internal environment deviates from a narrow range of acceptable states Homeostasis is the process by which an organism maintains its internal environment within a narrow range of conditions for optimal cell function in the face of a changing external environment Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment The internal environment is maintained in a state of dynamic constancy Although the word homeostasis implies a static unchanging state the internal environment is actually in a state of dynamic constancy The body actively adjusts to ongoing internal and external changes to maintain constant conditions Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment The internal environment is maintained in a state of dynamic constancy continued Examples of conditions within an animal s body that are regulated by homeostatic mechanisms include the following Temperature Water Salt concentrations Glucose concentrations pH acid base balance Oxygen Carbon Dioxide concentrations Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Why are cells so particular about their surroundings Animal cells are constantly generating and using large quantities of ATP to sustain life processes Continuous supplies of high energy molecules primarily glucose and O2 are required to carry out the reactions that generate ATP Thus energy production helps explain the importance of glucose and oxygen levels Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Feedback systems regulate internal conditions Homeostatic mechanisms that maintain internal constancy are collectively known as feedback systems There are two types of feedback systems Negative feedback which counteracts the effects of changes in the internal environment to maintain homeostasis Positive feedback which drives rapid self limiting changes such as those that occur when a mother gives birth Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Negative feedback reverses the effects of changes The most important mechanism governing homeostasis is negative feedback where a change in the environment causes responses that feed back and counteract the change The overall result of negative feedback is a return of the system to its original condition Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Negative feedback reverses the effects of changes continued There are three principal components to negative feedback systems A sensor which detects the current condition A control center which compares that condition to the desired state called the set point An effector which produces an output that restores the desired condition Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Negative feedback systems that control the heating of a home can be compared to those that control body temperature Home temperature is regulated by negative feedback In a home the sensor is a thermometer the control center is a thermostat and the effector is a heater The thermometer detects the room temperature and sends that information to the thermostat where the actual temperature is compared to the set point of the desired temperature Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Home temperature is regulated by negative feedback continued If the actual temperature is below the set point the thermostat signals the heater to turn on and generate heat The heater warms the room restoring the temperature to the set point which causes the thermostat to turn off the heater Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Negative feedback maintains body temperature The temperature control center is located in the hypothalamus a part of the brain that controls many homeostatic responses The set point for most people is between 97 and 99 F Nerve endings in the hypothalamus abdomen skin and large veins act as temperature sensors and transmit this information to the hypothalamus Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Negative feedback maintains body temperature continued If the body temperature falls below the set point the hypothalamus activates effector mechanisms that raise body temperature These mechanisms include shivering blood vessel constriction and increased metabolic rate When body temperature is restored the sensors signal the hypothalamus to switch off the actions that generate and conserve heat Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Negative feedback maintains body temperature continued The body s temperature controls system can also act to reduce body temperature if it rises over the set point The hypothalamus sends out signals that cause the blood vessels leading to the skin to dilate allowing warm blood to flow to the skin where it can be radiated out to the air Sweat glands secrete fluid cooling the body by evaporating water from the skin Fatigue and discomfort cause the body to slow down so the body generates less heat Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 31 1 Homeostasis How Do Animals Regulate Their Internal Environment Positive feedback enhances the effects of changes In positive feedback a change produces a response
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