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The Human Body:An Orientation
Chapter 1
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Overview of Anatomy and Physiology
Anatomy Study of structure
Subdivisions: Gross or macroscopic (e.g., regional, systemic, and surface
anatomy) Microscopic (e.g., cytology and histology) Developmental (e.g., embryology)
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Overview of Anatomy and Physiology
Physiology Study of the function of the body Subdivisions based on organ systems
(e.g., renal or cardiovascular physiology) Often focuses on cellular and molecular level
Body's abilities depend on chemical reactions in individual cells
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Principle of Complementarity
Anatomy and physiology are inseparable Function always reflects structure What a structure can do depends on its specific form
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Figure 1.2 Examples of interrelationships among body organ systems.
Digestive system Takes in nutrients, breaks them down, and eliminates unabsorbed matter (feces)
Food O2 CO2
Respiratory systemTakes in oxygen and eliminates carbon dioxide
Cardiovascular systemVia the blood, distributes oxygen and nutrients to all body cells and delivers wastes and carbon dioxide to disposal organs
BloodCO2
O2
Heart
Nutrients
Interstitial fluid
Integumentary system Protects the body as a whole from the external environment
Nutrients and wastes pass between blood and cells via the interstitial fluid
Feces Urine
Urinary system Eliminates nitrogenouswastes andexcess ions
Hierarchy of Structural Organization
Chemical Cellular Tissue Organ Organ System Organism
Homeostasis
The ability of the body to maintain relatively stable internal conditions even though there is continuous change in the outside world
A state of dynamic equilibrium The body functions within relatively narrow limits All body systems contribute to its maintenance
Control Mechanisms
Regardless of the factor or event (variable) being regulated, all homeostatic control mechanisms have at least three interdependent components
Receptor (stimuli of change is detected) Control center (determines response) Effector (bodily response to the stimulus)
Control Mechanisms
Regulation of homeostasis is accomplished through the nervous and endocrine systems
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Figure 1.4 Interactions among the elements of a homeostatic control system maintainstable internal conditions.
Slide 1
Output: Information sentalong efferent pathway toeffector.
Input: Informationsent along afferentpathway to controlcenter.
3
Receptordetectschange.
2
Stimulus produceschange invariable.
1
4
Responseof effectorfeeds back toreduce theeffect ofstimulus andreturnsvariableto homeostatic level.
5
ControlCenter
Afferentpathway
Efferentpathway
Receptor Effector
BALANCE
IMBALANCE
IMBALANCE
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Figure 1.4 Interactions among the elements of a homeostatic control system maintainstable internal conditions.
Slide 2
Stimulus produceschange invariable.
1
BALANCE
IMBALANCE
IMBALANCE
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Figure 1.4 Interactions among the elements of a homeostatic control system maintainstable internal conditions.
Slide 3
Stimulus produceschange invariable.
1
Receptordetectschange.
2
BALANCE
IMBALANCE
IMBALANCE
Receptor
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Figure 1.4 Interactions among the elements of a homeostatic control system maintainstable internal conditions.
Slide 4
Afferentpathway
Stimulus produceschange invariable.
1
Receptordetectschange.
2
Input: Informationsent along afferentpathway to controlcenter.
3
BALANCE
IMBALANCE
IMBALANCE
Receptor
ControlCenter
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Figure 1.4 Interactions among the elements of a homeostatic control system maintainstable internal conditions.
Slide 5
Afferentpathway
Efferentpathway
Stimulus produceschange invariable.
1
Receptordetectschange.
2
Input: Informationsent along afferentpathway to controlcenter.
3
BALANCE
IMBALANCE
IMBALANCE
Receptor
ControlCenter
Effector
Output: Information sentalong efferent pathway toeffector.
4
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Figure 1.4 Interactions among the elements of a homeostatic control system maintainstable internal conditions.
Slide 6
Afferentpathway
Efferentpathway
Stimulus produceschange invariable.
1
Receptordetectschange.
2
Input: Informationsent along afferentpathway to controlcenter.
3
BALANCE
IMBALANCE
IMBALANCE
Receptor
ControlCenter
Effector
Output: Information sentalong efferent pathway toeffector.
4
Responseof effectorfeeds back toreduce theeffect ofstimulus andreturnsvariableto homeostatic level.
5
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Negative Feedback
Most feedback mechanisms in body Response reduces or shuts off original stimulus
Variable changes in opposite direction of initial change
Examples Regulation of body temperature (a nervous system mechanism) Regulation of blood volume by ADH (an endocrine system
mechanism)
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Figure 1.5 Body temperature is regulated by a negative feedback mechanism.
Control Center(thermoregulatory
center in brain)
Afferentpathway
Efferentpathway
ReceptorsTemperature-sensitivecells in skin and brain)
EffectorsSweet glands
Sweat glands activated
ResponseEvaporation of sweatBody temperature falls;stimulus ends
Body temperaturerises
Stimulus: Heat
ResponseBody temperature rises;stimulus ends
EffectorsSkeletal muscles
EfferentpathwayShivering begins
BALANCE
IMBALANCE
IMBALANCE
Afferentpathway
Control Center(thermoregulatory
center in brain)
ReceptorsTemperature-sensitivecells in skin and brain
Stimulus: Cold
Body temperaturefalls
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Negative Feedback: Regulation of Blood Volume by ADH
Receptors sense decreased blood volume Control center in hypothalamus stimulates pituitary gland
to release antidiuretic hormone (ADH) ADH causes kidneys (effectors) to return more water to
the blood
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Positive Feedback
Response enhances or exaggerates original stimulus May exhibit a cascade or amplifying effect Usually controls infrequent events that do not require
continuous adjustment Enhancement of labor contractions by oxytocin (chapter 28) Platelet plug formation and blood clotting
Control Mechanisms
A chain of events . . . Stimulus produces a change in a variable Change is detected by a sensory receptor Sensory input information is sent along an afferent
pathway to control center Control center determines the response Output information sent along efferent pathway to activate
response Monitoring of feedback to determine if additional response
is required
Negative Feedback Mechanisms
Most control mechanisms are negative feedback mechanisms
A negative feedback mechanism decreases the intensity of the stimulus or eliminates it
The negative feedback mechanism causes the system to change in the opposite direction from the stimulus
Example: home heating thermostat
Positive Feedback Mechanisms
A positive feedback mechanism enhances or exaggerates the original stimulus so that activity is accelerated
It is considered positive because it results in change occurring in the same direction as the original stimulus
Positive feedback mechanisms usually control infrequent events such as blood clotting or childbirth
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Positive Feedback
Response enhances or exaggerates original stimulus May exhibit a cascade or amplifying effect Usually controls infrequent events that do not require
continuous adjustment Enhancement of labor contractions by oxytocin (chapter 28) Platelet plug formation and blood clotting
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Figure 1.6 A positive feedback mechanism regulates formation of a platelet plug. Slide 1
Releasedchemicalsattract moreplatelets.
Positivefeedbackloop
Plateletsadhere to site andrelease chemicals.
Feedback cycle endswhen plug is formed.
Platelet plugis fully formed.
Break or tearoccurs in bloodvessel wall.
Positive feedback cycle is initiated.
1
23
4
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Figure 1.6 A positive feedback mechanism regulates formation of a platelet plug. Slide 2
Positive feedback cycle is initiated.
Break or tearoccurs in bloodvessel wall.
1
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Figure 1.6 A positive feedback mechanism regulates formation of a platelet plug. Slide 3
Positive feedback cycle is initiated.
Break or tearoccurs in bloodvessel wall.
1
Plateletsadhere to site andrelease chemicals.
2
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Figure 1.6 A positive feedback mechanism regulates formation of a platelet plug. Slide 4
Positivefeedbackloop
Positive feedback cycle is initiated.
Break or tearoccurs in bloodvessel wall.
1
Plateletsadhere to site andrelease chemicals.
2 Releasedchemicalsattract moreplatelets.
3
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Figure 1.6 A positive feedback mechanism regulates formation of a platelet plug. Slide 5
Positivefeedbackloop
Feedback cycle endswhen plug is formed.
Positive feedback cycle is initiated.
Break or tearoccurs in bloodvessel wall.
1
Plateletsadhere to site andrelease chemicals.
2
Platelet plugis fully formed.
4
Releasedchemicalsattract moreplatelets.
3
© 2013 Pearson Education, © 2013 Pearson Education, Inc.Inc.
Homeostatic Imbalance
Disturbance of homeostasis Increases risk of disease Contributes to changes associated with aging
Control systems less efficient
If negative feedback mechanisms overwhelmed Destructive positive feedback mechanisms may take over (e.g., heart
failure)
Homeostatic Imbalances
Most diseases cause homeostatic imbalances (chills, fevers, elevated white blood counts etc.)
Aging reduces our ability to maintain homeostasis
Heat stress