Download - Homeostasis I
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