Mean77.7

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EXAM 1
Mean 77.7 Median 80 S.D. 12.5 Max 100
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Conserving Water
2. Reduced Water Loss in Excretion
K-rat (slang)
Kangaroo Rat All water needed to survive is
metabolized from dry seeds.
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K-rat urine is 3-4xs more concentrated than our
own urine! HOW?

• What Kidneys Do
• maintain ion concentration
• maintain water volume
• remove metabolic end products (like urea)
• remove foreign substances

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Highly Recommended Reading in Text pp. 990-999
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Basic unit of vertebrate kidney is the
nephron. Our kidney has 1,000,000 nephrons.
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Nephron is surrounded by interstitial
fluid Fluid has high NaCl
Figure 51.9
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Top of nephron
300 milliosmoles/liter
Concentration of interstitial fluid increases
1200 milliosmoles/liter
Bottom of nephron
Figure 51.9
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Bowmans capsule
glomerulus
Water glucose, amino acids, ions pushed from
glomerulus into Bowmans capsule.
Means active transport
Means diffusion
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loop of Henle
Extends into concentration gradient. BUT little
change in concentration of filtrate!!
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loop of Henle
Water diffuses out of descending loop NaCl
diffuses out of thin ascending loop Cl- pumped
out of thick ascending loop, Na diffuses down
electrical gradient.
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collecting duct
Water diffuses OUT OF DUCT. Urea and other
solutes become highly concentrated. Urine flows
to bladder.
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So why the loop of Henle?? Loop generates and
maintains concentration gradient in interstitial
fluid, by moving NaCl out of the loop. Loop
shape causes countercurrent multiplier effect.
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Back to kangaroo rats
Kangaroo rats have very long loops of Henle,
Which generate a very steep concentration
gradient, Allowing for very concentrated urine.
Frogs, which live in wet habitats, have NO loops
of Henle. Urine has same osmolarity as tissues.
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Conserving Water
3. Reduced Water Loss in Breathing

• Live in very arid deserts
• Weigh up to 1500 lbs.
• Wild camels in Gobi only
• Ancestors lived in North America

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Camels can withstand extreme water loss

• Last 7 days without H2O or food
• Tolerate 30 loss of weight in H2O
• But water NOT stored in hump (fat is)

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Water Conservation in Camels

• Do not pant (saving H20 loss from lungs)
• Sweat only a little
• Nose adapted to reduce H20 loss from lungs

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Conserving Water
3. Reduced Water Loss in Breathing
When a camel twitches nose, incoming air is
cooled, and moisture from outgoing air condenses
on nasal turbinates.
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Turbinates are whorls of tissue found in all
mammal noses. Camel turbinates have HUGE surface
area.
Strategy of ? SV ratio
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Camel noses seem like good design. The agent
of good design is natural selection. The good
designs eat the bad designs
BUT natural selection is NOT all-powerful. Henc
e, designs may not be perfect.
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The Pandas Thumb
Giant pandas use thumb to strip bamboo. Thumb
is a modified wrist bone.
The pandas thumb is a somewhat clumsy, but
workable solution. It wins no prize in an
engineers derby.
-- Stephen Jay Gould
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The Panda Principle
Natural selection does not build structures from
scratch. But uses what is available to be
modified. Hence, biological traits may often
fall short of being the ideal design.
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Tuesday, February 21 7pm Center for Creative
Photography Free to the Public Biological
Evolution What It Is and What It Isn't Joanna
Masel Assistant Professor Ecology and
Evolutionary Biology
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Gas Exchange in Animals Aerobic cellular
respiration requires O2 and generates
CO2. Animals must acquire O2 and get rid of
CO2. O2 in by diffusion CO2 out by diffusion
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Diffusion
permeable membrane
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Ficks Law of Diffusion
(P2 P1)
Rate of Diffusion
k A
D
k constant A area for gas exchange (P2
P1) difference in pressure across
barrier D distance across barrier
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O2
CO2
Multicellular organisms face a basic
problem diffusion of gases to and from cells
takes too long. A low, D long, (P1-P2) low
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Solution 1 Be hollow
Phylum Porifera Sponge
Phylum Cnidaria Hydra
? SV ratio ? A
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Solution 2 Be flat
? SV ratio ? A
Phylum Platyhelminthes Flatworm
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Solution 3
breathing
organ

internal transport system
Examples. vertebrate gas exchange fish gills
circulatory system mammal lungs circulatory
system
?A, ?D, ?(P1-P2)
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• Strategies for Gas Exchange
• Fish Gills
• Surface folding

Cutaway showing gill layers
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folds upon folds upon folds
? A in Ficks Law
Figure 48.5
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Strategies for Gas Exchange Fish Gills 2.
Thin-walled cells
Cells of gill have thin walls.
? D, the path of diffusion, between cell and
capillary
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Strategies for Gas Exchange Fish Gills 3.
Ventilation
Tunas, mackerels, anchovies swim constantly with
mouth open water flows through .
Most fish Gulp water then open gill flaps, then
gulp again. This allows for ventilation when
resting.
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Ventilation moves O2-depleted, CO2 rich water
away from gill membrane
This is equivalent to ?(P2 P1) in Ficks Law.
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Strategies for Gas Exchange Fish Gills 4.
Countercurrent Exchange
Blood and water flow in opposite directions,
hence countercurrent flow.
Figure 48.5
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Countercurrent Flow Improves Exchange!
Concurrent flow
H2O
X
O2
X
blood
Countercurrent flow
80
60
40
100
90
O2
???(P2 P1)
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• Summary Strategies for Gas Exchange
• Fish Gills
• Surface folding
• Thin-walled cells
• Ventilation
• Counter-current exchange

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• Gas Exchange on Land
• Theoretically less of a problem
• more O2 in unit volume of air than water
• gases diffuse much faster in air than water
• BUT on land, another problem
• water lost from moist respiratory surfaces

TRADEOFF maximizing gas exchange versus
minimizing water loss
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Solution to Tradeoff Internal Lungs
bad air out
good air in
Water loss minimized by enclosing respiratory
membranes
O2
CO2
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In a space of finite volume One sac or two?
Two sacs or many?
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Vertebrate lungs are networks of branching pipes
ending in many blind sacs.
? A in Ficks Law
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Strategies for Gas Exchange Vertebrate Lung

• Numerous, tiny air sacs

Figure 48.10
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alveoli
Figure 48.10
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2. Thin-walled cells ? D
Figure 48.10
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Strategies for Gas Exchange Vertebrate Lung
3. Ventilation
Air is ventilated by inflation and deflation of
lungs Requires energy!
Figure 48.10
?(P2 P1)
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• Strategies for Gas Exchange
• Vertebrate Lung
• Numerous, tiny air sacs
• Thin-walled cells
• Ventilation
• Counter-current exchange?

NO!
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Why No Counter-Current Exchange? Because
breathing is tidal
Air moves in, then out, like the
tides countercurrent flow not possible.
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Tidal breathing is bad design

• Countercurrent exchange not possible.
• During part of the cycle, no fresh air moving in.
  
• During part of the cycle, flow velocity 0.
• Some bad air left behind.

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Why Flawed Design?
Answer Lungs evolved as outpocketings of the gut.
adult frog
mammals
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The Pandas Lung
Terrestrial vertebrate lung design reflects the
Panda Principle. Natural selection exploited what
was available for a lung. The lung is effective
design, but NOT perfect.
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• Special Challenges for Birds
• Flight metabolically expensive.
• Air thin at high altitudes (O2 at low partial
  pressure).
• To fly efficiently, bird (and lungs) must weigh
  little.

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Extreme Makeover, Lung Edition
Bird Lungs
1. Numerous large air sacs 2. Flow-through
construction 3. Cross-current exchange
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Figure 48.7
parallel tubes called parabronchi
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Air in parabronchi blood in capillaries travel
at right angles to each other. cross-current
flow
parabronchus
Red for blood, Blue for air
Figure 48.7
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parabronchi
Cross-current flow more efficient than concurrent
flow
??(P2 P1)
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parabronchi
inhalation
Cycle 1
exhalation
On exhalation, air flows through parabronchi
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inhalation
Cycle 2
exhalation
On next inhalation, air flows through parabronchi
in same direction!
No more tidal flow!!
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Air sacs act as series of bellows to push air
continuously through parabronchi.
http//www.ivis.org/advances/Anesthesia_Gleed/ludd
ers2/chapter_frm.asp
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• Summary Strategies for Gas Exchange
• Bird Lungs
• Lightweight solution using air sacs
• Flow-through lung (no tidal rhythm)
• Cross-current exchange

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Flight Led to Lungs? Or Lungs Led to Flight?
? Recent data suggest that O2 levels suppressed
worldwide 175 - 275 mya.
? Conditions spurred evolution of flow-through
breathing system in Saurischian dinosaurs.
? New lung design paved way for evolution of
flight in birds.
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Breathing in Insects Organism-wide network of
branching pipes
? SV ratio!
Every cell is close to a tracheole.
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Spiracles open and close to control ventilation
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One reason we do not have giant insects is
that tracheole walls would collapse at large
sizes!