1. Plan of Human Body Figure 1.4
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Figure 1.4

2. The 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
The Body’s External Environment
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3. The Body’s Internal Environment
Internal environment = fluid surrounding cells
The Body’s Internal Environment
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4. Exchange Between External and Internal Environment
Between blood and external environment
Lungs
Gastrointestinal tract
Kidneys
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5. Body 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)
Body Fluid Compartments
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6. Body Fluid Compartments
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Figure 1.5

7. II. Homeostasis: A Central Organizing Principle of Physiology
Negative Feedback Control in Homeostasis
Homeostasis in Action: Thermoregulation
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8. Process of maintaining stable internal environment compatible for life
Most organ systems contribute to homeostasis
Exception: reproductive system
Homeostasis
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9. Negative Feedback Control in Homeostasis
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)
Negative Feedback Control in Homeostasis
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10. Negative 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
Negative Feedback Mechanisms
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11. Negative Feedback Control of Car Speed
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Figure 1.6a, b

12. Negative Feedback Control of Body Temperature
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Figure 1.6c, d

13. Negative Feedback Loop
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Figure 1.7

14. Positive Feedback Loop
Positive feedback loops cause a rapid change in a variable.
Positive Feedback Loop
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Figure 1.8

15. Homeothermic animals – regulate body temperature within a narrow range
Poikilothermic animals – do not regulate body temperature
Thermoregulation
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16. Homeothermic 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
Homeothermic Animals
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17. Mechanisms of Heat Transfer Between Body 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
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18. Components of Thermoregulatory System
Thermoregulatory system maintains core body temperature
Detectors - thermoreceptors (central and peripheral)
Integrator - hypothalamus
Effectors - sweat glands, blood vessels in skin, skeletal muscles
Components of Thermoregulatory System
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19. 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
Thermoneutral Zone
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20. Negative Feedback Control of Body Temperature
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Figure 1.9a, b

21. Thermoregulation Figure 1.9c
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Figure 1.9c

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