UNIT%203:%20HOMEOSTASIS

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UNIT 3 HOMEOSTASIS

• Ch 7 Maintaining an Internal Balance
• - Homeostasis
• - Feedback Loops
• - Thermoregulation

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HOMEOSTASIS

• Although the world around varies over time, our
  bodies maintain a stable internal environment
• 37 degrees Celsius, 0.1 blood glucose, blood pH
  of 7.35
• Homeostasis the maintenance of a steady-state
  internal environment despite a constantly
  changing external environment.
• Homeostasis is called a dynamic equilibrium as it
  allows all body systems to work within an
  acceptable range.
• Dynamic equilibrium is a condition that remains
  stable within fluctuating limits.
• Blood pressure, blood pH, and blood glucose
  levels and body temperature...all work within a
  small acceptable range.
• To do this the body needs monitoring and feedback
  systems,
• Kidneys monitor water levels
• Pancreas regulates blood sugar levels
• Hypothalamus regulates body temperature and
  osmotic pressure...

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• 3 important components to these systems
• A monitor which notices changes in the normal
  state and sends messages to the
• Coordinating Centre which recognizes an organ is
  working outside its normal limits and sends a
  message to a
• Regulator which returns the body to its normal
  state.
• Example When exercising CO2 levels in the blood
  increase due to an increase in cellular
  respiration.
• Sensors in the blood vessels notice this and
  pass the information to the brain.
• The brain analyzes the information, sends a
  message to the muscles around the chest cavity.
• The muscles allow for deeper and more frequent
  inhalation/exhalation. This gets rid of the CO2
  returning levels in the blood back to normal.

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FEEDBACK LOOPS

• The way homeostasis is maintained is by means of
  feedback loops.
• The body uses mainly negative feedback loops,
  processes in which a mechanism is activated to
  bring the body back to its normal level, to
  maintain a steady-state.
• Example Room temperature falls below 20 degrees
  Celsius
• the thermometer sends a message to the thermostat
  to turn on the furnace.
• Once the room reaches 20 again, the thermostat
  turns the furnace off.
• Negative feedback refers to the fact that a
  change in a variable triggers the coordinating
  center to counteract any further changes.
• Therefore small changes are kept from becoming
  large.

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http//www.okc.cc.ok.us/biologylabs/Images/Homeost
asis20Images/Feedback_loop.gif
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• Positive feedback systems
• less common
• designed to accept changes in the body and
  further promote them
• Therefore, small changes become amplified.
• Allow for the body to accomplish something in a
  very small amount of time.
• Example before and after pregnancy/labour.
• Decrease in progesterone --gt contraction in the
  uterus --gt cause oxytocin release --gt stronger
  contractions --gt baby moves closer to the uterine
  opening --gt more oxytocin released --gt even
  stronger contractions ( --gt baby eventually
  expelled ) --gt contractions stop, which stops
  oxytocin ) ) ).
• Hmwk p 337 1,2,4,5,6,9

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THERMOREGULATION

• The maintenance of body temperature within a
  range in which the organism functions optimally
  (optimal range).
• Ectotherms animals which depend on air
  temperature to maintain their metabolic rate, ie.
  invertebrates (organisms without backbones fish,
  amphibians, reptiles)
• Their activity is governed by their environment.
• This limitation is overcome by different
  behaviours or evolutionary adaptations reptiles
  sun themselves, tuna's circulatory system keeps
  their internal organs at a higher temperature
  than the surrounding water.
• Endotherms animals which are able to maintain
  their body temperature regardless of the
  environmental conditions (birds and mammals).
• If the temperature drops then metabolic rate
  increases and the organism shivers to create
  heat.

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• The hypothalamus is the region of the brain
  responsible for maintaining a constant internal
  temperature.
• Important to note that the core temperature of
  the body is usually different from the peripheral
  temperature at the extremities.
• How we respond to temperature change (Figure 2, p
  339).
• Too hot
• Sensors in the brain tell the hypothalamus it is
  too hot
• Sends a nerve impulse to
• the sweat glands to start sweating and to
• the skin blood vessels to dilate to increase the
  amount of blood reaching the skin as the skin can
  give off the excess heat
• Both these changes cause body temperature to
  lower back to normal levels.

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http//fig.cox.miami.edu/cmallery/150/physiol/c44
x10thermo-reg.jpg
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• Too cold
• Thermoreceptors in the skin tell the hypothalamus
  it is too cold
• Sends nerve signals to
• the skin blood vessels to constrict and reduce
  the amount of blood flow to the skin thus
  preventing heat loss,
• the muscles to contract and cause us to shiver to
  generate heat.
• Smooth muscles around body hair contract causing
  the hair to become erect to conserve heat
• Body temperature increases back to normal levels.
• Homework p341 1,2,3,5,7,8,10