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Survival Needs
Life depends on five environmental
factors
• water
• food
• oxygen
• heat
• pressure
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Survival Needs
Survival Needs
Oxygen (Gas)
Water
-
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- one-fifth of air
- used to release energy from nutrients
most abundant substance in body
required for metabolic processes
required for transport of substances
regulates body temperature
Heat
- form of energy
- partly controls rate of metabolic reactions
Food
Pressure
- application
- provides necessary nutrients
- supplies energy
- supplies raw materials
of force on an object
- atmospheric pressure – important for breathing
- hydrostatic pressure – keeps blood flowing
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Feedback Mechanisms
Homeostasis
Maintenance of a stable internal environment
Negative feedback
• Includes most homeostatic control
mechanisms
• Homeostatic imbalance – a disturbance
in homeostasis resulting in disease
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• Shuts off the original stimulus, or reduces
its intensity
• Works like a household thermostat
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Homeostatic Mechanisms
The body communicates through neural
and hormonal control systems
Monitor aspects of the internal
environment and corrects any changes
•Receptors - provide information about
stimuli
•Control center - tells what a particular
value should be (includes a set point)
•Effectors - elicit responses that change
conditions in the internal environment
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Feedback Mechanisms
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Feedback Mechanisms
STIMULUS: DECREASE IN EXTERNAL TEMPERATURE
↑
STIMULUS:
IN
H2O INTAKE
STIMULUS:
DEHYDRATION
CONTROL CENTER
RECEPTOR
RECEPTOR
EFFECTOR
EFFECTOR
RESPONSE
RESPONSE
CONTROL
CENTER
RECEPTOR
EFFECTOR
RESPONSE
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Feedback Mechanisms
Positive Feedback
• Increases the original stimulus to
push the variable farther
• In the body this occurs only in
blood clotting and child birth
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