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Plan of Human Body Plan of Human Body Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 1.4

Homeostasis I

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Plan of Human BodyPlan of Human Body

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 1.4

The Body’s External EnvironmentThe Body’s External Environment

◦Interior of body separated from external environment by a layer of epithelial tissue

◦Lumen of respiratory system, gastrointestinal system, and urinary system are part of external environment

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

The Body’s Internal EnvironmentThe Body’s Internal EnvironmentCopyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Internal environment = fluid surrounding cells

Exchange Between External and Exchange Between External and Internal EnvironmentInternal Environment

◦Between blood and external environment Lungs Gastrointestinal tract Kidneys

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Body Fluid CompartmentsBody Fluid Compartments

◦Internal environment = fluid surrounding cells = extracellular fluid (ECF)

◦70 kg man-Total body water = 42 liters• 28 liters intracellular fluid (ICF)• 14 liters extracellular fluid (ECF)

-3 liters plasma-11 liters interstitial fluid (ISF)

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Body Fluid CompartmentsBody Fluid CompartmentsCopyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 1.5

II. Homeostasis: A Central Organizing II. Homeostasis: A Central Organizing Principle Principle of Physiologyof Physiology

• Negative Feedback Control in HomeostasisNegative Feedback Control in Homeostasis

• Homeostasis in Action: ThermoregulationHomeostasis in Action: Thermoregulation

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

HomeostasisHomeostasis

Process of maintaining stable internal environment compatible for life

◦Most organ systems contribute to homeostasis

◦Exception: reproductive system

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Negative Feedback Control in Negative Feedback Control in HomeostasisHomeostasis

◦Primary mechanism for maintaining homeostasis

◦External change triggers change in regulated variable in internal environment triggers reaction to oppose the change and return regulated variable toward normal (set point)

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Negative Feedback MechanismsNegative Feedback Mechanisms

◦Set point = desired level of regulated variable◦Sensors detect level of regulated variable and

provide input to integrating center◦Integrating center compares set point to actual

level of regulated variable◦Error signal = difference between actual level and

set point◦Integrating center sends output to effectors to

return regulated variable toward set point

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Negative Feedback Control of Car Negative Feedback Control of Car SpeedSpeed Copyright © 2005 Pearson Education,

Inc., publishing as Benjamin Cummings. Figure 1.6a, b

Negative Feedback Control of Negative Feedback Control of Body TemperatureBody Temperature Copyright © 2005 Pearson Education,

Inc., publishing as Benjamin Cummings. Figure 1.6c, d

Negative Feedback LoopNegative Feedback LoopCopyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 1.7

Positive Feedback LoopPositive Feedback LoopCopyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Positive feedback loops cause a rapid change in a variable.

Figure 1.8

ThermoregulationThermoregulation

◦Homeothermic animals – regulate body temperature within a narrow range

◦Poikilothermic animals – do not regulate body temperature

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Homeothermic AnimalsHomeothermic Animals

◦Normal body temperature = set point Differs in animal species Humans: 37oC (98.6oF)

◦Hypothermia = decrease in body temperature◦Hyperthermia = increase in body temperature

above 41oC, dangerous above 43oC, deadly

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Mechanisms of Heat Transfer Between Mechanisms of Heat Transfer Between Body and External EnvironmentBody and External Environment

◦Radiation - thermal energy as electromagnetic waves

◦Conduction - thermal energy through contact◦Evaporation - heat loss through evaporation of

water insensible water loss sweating

◦Convection - heat transfer by movement of fluid or air

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Components of Thermoregulatory Components of Thermoregulatory SystemSystem

◦Thermoregulatory system maintains core body temperature

◦Detectors - thermoreceptors (central and peripheral)

◦Integrator - hypothalamus◦Effectors - sweat glands, blood vessels in

skin, skeletal muscles

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Thermoneutral ZoneThermoneutral Zone

Range of outside temperature where alterations in blood flow alone regulates

body temperature

25-30oC◦Body temperature increase:

blood flow to skin increases◦Body temperature decrease:

blood flow to skin decreases

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Negative Feedback Control of Negative Feedback Control of Body TemperatureBody Temperature Copyright © 2005 Pearson Education,

Inc., publishing as Benjamin Cummings. Figure 1.9a, b

ThermoregulationThermoregulation Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 1.9c

FeverFever

◦Fever accompanies infections◦White blood cells secrete pyrogens◦Body temperature set point increases◦Fever enhances immune response

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.