HOMEOSTASIS:
MAINTAINING AN INTERNAL
BALANCE
SBI 4U, December 12th, 2012
Maintaining an Internal Balance
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Ray Zahab vs. Fennec Fox
Fennec fox  ears allow for efficient hearing and
act as radiator
Maintaining and Internal Balance
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Homeostasis: the physiological state of the body in
which the internal physical and chemical conditions
are maintained within an acceptable or tolerable
range that is suitable for essential biological
processes
Dynamic state
Maintaining an Internal Balance
Body has several conditions that must be monitored.
Such as:
-internal temperature
-hormone levels
-pH
-flow and concentration of glucose and other solutes
*some tolerable ranges are narrow, while others are
more broad*
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The Internal Environment
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Purpose of homeostasis: to maintain internal physical and
chemical conditions that are appropriate for the cells to
function properly
Internal environment: the extracellular fluid, which consists
of the fluid that surrounds the cells and tissues in the body
and the plasma portion of the blood
Focus on fluid outside of the cells
Organ Systems Involved in Homeostasis
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Nervous System
Endocrine System
Muscular System
Integumentary System
Excretory System
Reproductive System
Organ Systems Involved in Homeostasis
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All of the organ systems are coordinated to carry out
the tasks necessary for the survival of the organism. No
matter how simple or complex the animal, these functions
include:
Taking in nutrients and other required chemicals,
processing and excreting
Synthesizing proteins, fats and carbs
Sensing and responding to changes in external
environment
Protecting body
Reproducing, protecting and feeding offspring
Organ Systems Involved in Homeostasis
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Homeostatic Mechanisms: a system that monitors internal
and external conditions and changes bodily functions to
maintain homeostasis
Ex: shivering in response to cold weather
Negative Feedback Mechanisms
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Primary mechanism of homeostasis
Negative feedback: the response of a system that acts to maintain
equilibrium by compensating for any changes made to the system
3 components: sensor, integrator and effector
Negative Feedback Mechanisms
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Sensor: consists of tissues or organs that detect any
change in external or internal factors
Info transmitted to integrator  acts as a
processing or control centre. Compares
environmental conditions with the optimal function
conditions called set points
Integrator activates the effector  the element of a
feedback system that acts to return the system to its
optimal state
Negative Feedback Mechanisms
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Antagonistic effects  response opposite to change
Ex: thermostat
Sensor measures temperature
Integrator compares the measures temperature to set point
Integrator activates electrical effector (furnace or air
conditioner)
Temperature returned to normal state
Negative Feedback in Animals
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Ex: humans
Neurons in preoptic region of hypothalamus
receive info from thermoreceptors
Hypothalamus compares info to set point
Hypothalamus activates effectors that induce
vasoconstriction in skin. Less thermal energy lost.
Body temperature increases
Positive Feedback Mechanisms
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Positive Feedback: the response of a system that
acts to increase the effect of any changes made to
the system
Do not result in homeostasis
Operate when a continuous increase in some
internal variable is required (ex: fight or flight)
Ex: childbirth contractions  release of oxytocin