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5/11/2017
Homeostasis
“The human body is not
a thing or substance,
given, but a continuous
creation. The human
body is an energy
system which is never
a complete structure;
never static; is in
perpetual inner selfconstruction and selfdestruction; we destroy
in order to make it
new.”
HOMEOSTASIS
• The bodies ultimate goal is to
maintain a stable internal
environment.
• “The human body is a machine
which winds its own springs.”
~Julien Offroy de la Mettrie, L'Homme
Machine
~Norman O. Brown
Homeostasis
Homeostatic Imbalance
• Dynamic Equilibrium
• Not a “steady state”, as there is
constant monitoring & adjusting
Disease
DEATH
Disease
Normal
Range
Disease
Disease
DEATH
Feedback Mechanisms
• Helps to keep the body within a
livable range
• Body tries to keep as close to a
set point as possible
• The LAST step in a series of
events controls the FIRST
• Disease = disturbance of
homeostasis
3. INPUT
Information sent along afferent pathway to control center
4. OUTPUT
Information sent along efferent pathway to effector
CONTROL CENTER
Afferent Pathway
RECEPTOR
1.STIMULUS
Produces change in variable
 Control systems get less effective
 Internal environment less stable
 Increased risk of illness
 Changes in body that we
associate with aging
Negative Feedback
Efferent pathway
EFFECTOR
2. RECEPTORS
Detect change
– Can be negative or positive
• WITH AGE:
BALANCE
5. RESPONSE
Effector reacts to information
• Can be negative or positive feedback
• CHANGE in one direction
causes body to return conditions
to “normal”
• The final step INHIBITS the
initial signal in the series
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EXAMPLE of Negative Feedback: Body Temperature Regulation Stimulus
Stimulus
TOO HOT
Thermorecptors TOO COLD
Sensory Neurons (Afferent)
Control Center (in Brain)
Motor Neurons (Efferent)
SWEAT
Skeletal Muscle Activates Glands Activate
SHIVER
Response
Examples
Positive Feedback
=
• CHANGE in one direction;
enhances & accelerates original
stimulus in a CASCADE effect
• The final step STIMULATES the
release of more initial signals
EXAMPLE of Positive Feedback: Blood Clotting
2. Platelets stick to site 3. Released chemicals 4. Feedback Cycle 1. Break in blood attract more platelets Ends When:
& release chemicals
vessel wall Platelet plug is fully formed
Homeostasis Examples
Homeostasis Examples
A sick child begins to sweat.
A butcher slices his finger
Regulation = body Temp.
Feedback = negative
Regulation = wound healing
Feedback = positive
Homeostasis Examples
Homeostasis Examples
Homeostasis Examples
A man faints in the L&D room
Snowy hunters shiver & huddle
Frightened teens heart beats
harder than normal
Regulation = blood pressure
Feedback = negative
Regulation = body temp.
Feedback = negative
Regulation = blood pressure
Feedback = negative
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Homeostasis Examples
Homeostasis Examples
Homeostasis Examples
Uterine stretching and fetal head
on cervix triggers labor
Toddler eats too much candy
Seamstress sews through her
finger
Regulation = labor & delivery
Feedback = positive
Regulation = blood glucose
Feedback = negative
Homeostasis Examples
Homeostasis Examples
Nursing mother’s milk supply
changes with baby’s need
Thirsty jogger drinks water
Regulation = nursing
Feedback = positive
Regulation = wound healing
Feedback = positive
Questions?
Comments?
Regulation = hydration
Feedback = negative
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