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1. Homeostasis

2. What is homeostasis?
(same) (state)
• Regulation and
internal
maintenance of the
body
• The body works
best when internal
conditions are
within an acceptable
range; homeostasis
helps to do this

3. Feedback Loops
• Homeostasis controls internal conditions
with feedback loops
• NEGATIVE feedback loop – the product
inhibits the process that creates them
– Ex: control of body temperature, thermostat
– Common homeostatic mechanism
• POSITIVE feedback loop – the product
amplifies the process that creates them
– Ex: labor, global warming

4. Feedback Loop
NEGATIVE POSITIVE

5. Homeostasis Examples
• Thermoregulation (temperature)
• Osmoregulation (water)
• Gas Exchange
• Blood Glucose
• Guard Cells
• Other examples:
– pH
– Blood pressure
– Hormone levels
– Metabolism

6. Thermoregulation
ORGAN IN CHARGE  BRAIN
• Hypothalamus scans
temperature of
blood as it passes
through
– Too high  blood
vessels dilate,
sweating occurs
– Too low  blood
vessels constrict,
shivering

7. Osmoregulation
• Regulation of the balance of
water and solutes (salt, ions)
in the body
• Aquatic Organisms:
– (Freshwater) Protists – don’t
forget about the contractile
vacuole!
– Freshwater fish – environment is
hypotonic to the fish; fish take
in lots of water
• Solution  fish excrete LOTS of
very dilute urine to conserve
solutes
– Saltwater fish – environment is
hypertonic to the fish; fish loses
water to osmosis
• Solution  fish have specialized
gills to excrete excess ions
FRESHWATER
SALTWATER

8. Osmoregulation
ORGAN IN CHARGE  BRAIN/KIDNEYS
• Terrestrial Animals
– Water is constantly
being lost through
evaporation,
perspiration, urination
• Water lost through
these avenues needs to
be replaced by drinking
and eating
– Concentration of urine
allows solutes to be
excreted while
conserving water
(kidneys)

9. Osmoregulation – Land Animals

10. Guard Cells (Plants) ORGAN IN CHARGE  LEAF
• Leaves take in CO2, release O2
and H2O through stomata
• Guard cells surround the
stomata
– Water abundant  water
pressure HIGH, stomata
OPEN, release water, CO2
enters
– Water scarce  water
pressure LOW, stomata
CLOSED, loss of water
limited
• Generally 
– Stomata open during the
day (photosynthesis)
– Stomata closed during the
night (decreased
photosynthesis, prevent
water loss)
– Exceptions  HOT DRY
conditions may result in
closed stomata during the
day

11. Gas Exchange in Mammals
ORGAN IN CHARGE  LUNGS
• Oxygen-rich air (poor in
CO2) is taken in during
inhalation; moves to
alveoli
• Oxygen-poor blood (rich
in CO2) vessels surround
the alveoli
• Passive transport moves
the oxygen from alveoli
into the blood, CO2 from
blood into the alveoli
• Oxygen delivered to
cells through the blood
vessels; CO2 expelled
during exhalation

12. Regulation of Blood Glucose
ORGAN IN CHARGE  PANCREAS
• Blood sugar too high:
– Pancreas releases
insulin; body cells
take in glucose and
moves it to long
term storage in
liver (glycogen)
• Blood sugar too low:
– Pancreas releases
glucagon;
stimulates liver to
break down stored
glycogen (into
glucose) and
release into
bloodstream