Transcript Homeostasis - BEHS Science

Chapter 44:
Maintaining a Constant
Internal Environment
(Homeostasis)
Body Temperature
 Enzymes: Rxn rates inc. 2-3
times with each 100 C temp. inc.
(until denatured)
 Each species has an optimal
temp. range for metabolic rxns
to be efficient
 Thermoregulation  Organisms
maintain their body temp within
optimal range (various methods)
Heat Gain/Loss
Heat Gain/Loss (HIGH to LOW)
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Conduction = molecule to molecule
(ie: hot concrete and feet in
summer)
Convection = heat transfer b/t object
and H2O or air moving across it
Radiation = electromagnetic waves
transferred as heat (ie: suns rays)
Evaporative Cooling = lowers temp
by releasing H2O as vapor (ie:
sweating)
Ectotherms and Endotherms
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Ectotherms (“cold-blooded”) maintain
a temperature close to external temp.
• Low metabolic requirements (little
heat generated)
• Most fish, reptiles, amphibians
Endotherms (“warm-blooded”)
maintain a constant temp. that may
vary significantly from external temp
(species dependent)
• High metabolic rate (lots of heat!)
• Humans, other mammals, and birds
Endotherms/Ectotherms
Endothermic Advantages
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Higher temp allows for inc. metabolic
rate
More energy is generated
Can perform more vigorous activities
for more sustained periods
Allows terrestrial life (more temp.
fluctuations than H2O)
Disadvantage : Require more
frequent meals for higher aerobic
resp. rate
Vasodilation and Vasoconstriction
 Vasodilation  Blood vessels
dilate (expand) in order to
release more heat
 Vasoconstriction  Blood vessels
constrict in order to limit heat
loss in the cold
Behavioral Controls
 Basking in the sun to raise body
temp
 Hibernation
 Migration to different climates
(birds)
 Inc or dec metabolic rate in
hot/cold temps
 Certain insects huddle to
generate more heat
Insulation
Hair
 Feathers
 Blubber, fat
 Reduces the loss of heat
 Allows maintenance of higher
body temps
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Insulation
Thermoregulation in Humans
Thermoregulation in Humans
 Heat receptors in skin
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Receptors send hot/cold signal to
hypothalamus (brain)
Hypothalamus regulates
vasodilation and vasoconstriction
Extreme Hot/Cold Environments
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Cryoprotectants  Certain
organisms (some frog eggs,
arctic fish) have a biologically
produced antifreeze
Heat shock proteins  Produced
in response to heat. Bind to
enzymes and other proteins to
inhibit denaturization
Hibernation
Bears, squirrels go into a
deep sleep during winter in
order to avoid harsh
conditions
 Very low energy demands
 Very low metabolic rate
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Hibernation
Osmoregulation (Water Balance)
 Organisms must balance their
water and solute concentrations
 Water uptake and loss must
remain essentially equal
 Cells could swell or shrivel
 Water flows from high water
potential (low [solute]) to low
water potential (high [solute])
Osmoregulators/Osmoconformors
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Osmoregulators maintain a constant
solute concentration different from
that of ext. environment
•Freshwater, terrestrial, some
marine
•Costs energy (active transport)
Osmoconformers maintain solute
concentration equal to that of
surroundings
•Many marine invertebrates
Osmoregulation
Waste Disposal
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Elimination of toxic materials is needed
to maintain homeostasis
Nitrogenous wastes are very toxic to
living cells
• Urea  Many terrestrial organisms,
lowest toxicity, high energy
requirement (humans)
• Uric Acid  Birds, insects reptiles,
least water lost
• Ammonia  Fish, aquatic organisms,
most toxic
Nitrogenous Waste
Selective Reabsorption and Secretion
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Organisms will filter
their wastes and
reabsorb anything
that may be of use
Accomplished in
tubules (present in
human kidneys)
May also secrete
more waste
materials into urine
Malpighian Tubules
Remove nitrogenous wastes from open
circulatory system of insects
Vertebrate Urinary System
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Kidneys
•Function in osmoregulation and
reabsorption
•Contain a network of tubules
Renal Artery  Blood to kidney
Renal Vein  Blood from kidney
Ureter  Carries urine to bladder
Bladder  Stores urine
Urethra  Tube that exits the body
Vertebrate Kidneys
 Two regions
•Renal cortex and renal medulla
 Contains millions of nephrons
•Microscopic tubules
 Glomerulus Network of
capillaries serving each nephron
with a blood supply
 Bowman’s Capsule  End of tubule
that surrounds the glomerulus
Human Kidney
Kidneys
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nephron and collecting duct are lined
by a transport epithelium
process filtrate to form urine
reabsorb solutes and water
•sugar, vitamins, and other organic
nutrients from the initial filtrate
and about 99% of the water
reduce 180 L of initial filtrate to
about 1.5 L of urine to be voided
Kidney Function
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Proximal Tubule  NaCl and H2O
reabsorption and pH regulation
Descending Loop of Henle  H2O
reabsorption
Ascending Loop of Henle  NaCl
reabsorption
Distal Tubule  K+ and NaCl balance,
pH regulation, some H2O reabsorbed
Collecting Duct  NaCl reabsorption,
H2O reabsorption
As it moves through the kidney, urine
becomes more concentrated with
unusable waste
Kidneys
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Kidneys give terrestrial
vertebrates the ability to
regulate their osmotic
balance
Without kidneys, life on land
would not be possible