Chapter 1
The Human
Body: An
Orientation
© Annie Leibovitz/Contact Press Images
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1.1 Form and Function of Anatomy &
Physiology
• Anatomy
– Study of the structure of body parts and their
relationship to one another
• 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
• Essential tools for the study of anatomy
– Mastery of anatomical terminology
– Observation
– Manipulation
– Palpation
– Auscultation
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1.1 Form and Function of Anatomy &
Physiology
• Physiology
– Study of the function of body parts; how they
work to carry out life-sustaining activities
– Subdivisions based on organ systems (e.g.,
renal or cardiovascular physiology)
– Often focuses on cellular and molecular levels of
the body
• Looks at how the body’s abilities are dependent on
chemical reactions in individual cells
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Overview of Anatomy and Physiology
• Essential tools for the study of physiology
– Ability to focus at many levels (from systemic to
cellular and molecular)
– Study of basic physical principles (e.g., electrical
currents, pressure, and movement)
– Study of basic chemical principles
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Complementarity of Structure and Function
• Anatomy and physiology are inseparable
– Function always reflects structure
– What a structure can do depends on its specific
form
– Known as the principle of complementarity of
structure and function
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Slide 1
Figure 1.1 Levels of structural organization.
Atoms
Organelle
Molecule
Smooth muscle cell
Chemical level
Atoms combine to form
molecules.
Cellular level
Cells are made up of
molecules.
Smooth muscle tissue
Cardiovascular
system
Heart
Blood
vessels
Tissue level
Tissues consist of similar types
of cells.
Blood vessel (organ)
Smooth muscle tissue
Connective tissue
Epithelial
tissue
Organ level
Organs are made up of different
types of tissues.
Organismal level
The human organism is made
up of many organ systems.
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Organ system level
Organ systems consist of different
organs that work together closely.
Interdependence of Body Functions
• Humans are multicellular, so to function,
individual cells must be kept alive
– Organ systems are designed to service the cells
– All cells depend on organ systems to meet their
survival needs
• There are 11 organ systems that work together
to maintain life
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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
Respiratory system
Takes in oxygen and
eliminates carbon dioxide
O2
CO2
Cardiovascular system
Via the blood, distributes oxygen
and nutrients to all body cells and
delivers wastes and carbon
dioxide to disposal organs
Blood
Heart
Nutrients
Interstitial fluid
CO2
O2
Urinary system
Eliminates
nitrogenous
wastes and
excess ions
Nutrients and wastes pass
between blood and cells
via the interstitial fluid
Feces
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Integumentary system
Protects the body as a whole Urine
from the external environment
1.4 Homeostasis
• Homeostasis is the maintenance of relatively
stable internal conditions despite continuous
changes in environment
– A dynamic state of equilibrium, always
readjusting as needed
– Maintained by contributions of all organ systems
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Homeostatic Controls
• Body must constantly be monitored and
regulated to maintain homeostasis
– Nervous and endocrine systems, as well as
other systems, play a major role in maintaining
homeostasis
– Variables are factors that can change (blood
sugar, body temperature, blood volume, etc.)
• Homeostatic control of variables involves three
components: receptor, control center, and
effector
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Homeostatic Controls (cont.)
• Receptor (sensor)
– Monitors environment
– Responds to stimuli (things that cause changes in
controlled variables)
• Control center
– Determines set point at which variable is maintained
– Receives input from receptor
– Determines appropriate response
• Effector
– Receives output from control center
– Provides the means to respond
– Response either reduces stimulus (negative feedback)
or enhances stimulus (positive feedback)
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Slide 1
Figure 1.4 Interactions among the elements of a homeostatic control system maintain stable internal conditions.
3 Input: Information
sent along afferent
pathway to control
center.
2 Receptor
Receptor
Control
Center
Afferent
pathway
Efferent
pathway
1 Stimulus
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sent along efferent
pathway to effector.
Effector
5 Response
detects change.
produces
change in
variable.
4 Output: Information
BALANCE
of effector feeds
back to reduce
the effect of
stimulus and
returns variable
to homeostatic
level.
Homeostatic Controls (cont.)
• Negative feedback
– Most-used feedback mechanism 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 glucose by insulin (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)
Afferent
pathway
Efferent
pathway
Receptors
Temperature-sensitive
cells in skin and brain
Effectors
Sweat glands
Sweat glands activated
Response
Evaporation of sweat
Body temperature falls;
stimulus ends
Body temperature
rises
BALANCE
Stimulus: Heat
Stimulus: Cold
Response
Body temperature rises;
stimulus ends
Body temperature
falls
Receptors
Temperature-sensitive
cells in skin and brain
Effectors
Skeletal muscles
Shivering begins
Efferent
pathway
Afferent
pathway
Control Center
(thermoregulatory
center in brain)
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Homeostatic Controls (cont.)
• Positive feedback
– Response enhances or exaggerates the original
stimulus
– May exhibit a cascade or amplifying effect as
feedback causes variable to continue in same
direction as initial change
– Usually controls infrequent events that do not
require continuous adjustment, for example:
• Enhancement of labor contractions by oxytocin
• Platelet plug formation and blood clotting
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Slide 1
Figure 1.6 A positive feedback mechanism regulates formation of a platelet plug.
1 Break or tear
occurs in blood
vessel wall.
Positive feedback
cycle is initiated.
2 Platelets
3 Released
chemicals
attract more
platelets.
Positive
feedback
loop
adhere to site
and release
chemicals.
Feedback cycle ends
when plug is formed.
4 Platelet plug
is fully formed.
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Homeostatic Imbalance
• Disturbance of homeostasis
– Increases risk of disease
– Contributes to changes associated with aging
• Control systems become less efficient
– If negative feedback mechanisms become
overwhelmed, destructive positive feedback
mechanisms may take over
• Heart failure
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