Announcements

1
Announcements

• Exam next week (Tuesday)!
• Will cover material through this Thursday
• Review session
• TODAY 730 9pm
• Irving 201 (This room)
• Additional OFFICE HOURS
• Thursday 1130 1230 2-4 p.m.
• Friday 9-10 a.m.
• Nikki Monday 1-230 pm
• Morgan ???

2
Study tips

• Outline the material weve covered in class so
  far.
• How are subtopics related to each other?
• What themes have come up more than once?
• What are the general principles, and how do they
  matter?
• Study actively
• Re-draw graphs,
• Conjure up equations,
• Write descriptions of phenomena in your own words
• Simply reading material does squat for your
  retention!

3
Power relationships

• Power relationship
• Y b ax
• log Y log b x log a

4
Applied to Q10 effect

• Y b ax
• Rate 2 Rate1 Q10((T2-T1)/10)
• b Rate 1
• A Q10

Log R2 log R1 log Q10 ((T2-T1)/10)
5
Surviving freezing body temperatures

• Freezing is dangerous due to
• ice crystal formation (ice is sharp!)
• Dehydration (all your water gets bound up in
  ice!)
• Two main strategies
• Freeze avoiders
• Prevent ice formation
• Do NOT tolerate freezing
• Freeze tolerators
• Control ice formation
• Tolerate partial to near total freezing

6
What makes a solution freeze?
1) Temperature 2) Time 3) Presence of nuclei
Ice crystallization needs a little help Very
pure water will freeze at -20ºC!
7
Scholanders experiment (1957)
Freezing points Seawater (1000 mOsm)
-1.86ºC Vertebrate plasma (300mOsm) -0.56ºC
-1.5ºC seawater
Live fish
These fish are unstably supercooled Presence
of ice nuclei cause fish to snap freeze
8
Freeze tolerators control freezing

• Produce ice nucleating proteins in extracellular
  fluid to encourage controlled ice formation
• Use antifreeze to control ice growth
• Use antifreeze compounds inside cells
• Stabilize membranes with sugars and amino acids

e.g. Rana sylvatica wood frog Tolerates over
70 of body water freezing! Manufactures huge
quantities of glucose Selectively allows organ
dehydration
9
Antifreeze proteins are more effective than
solutes
However, you dont need a special gene to produce
sugar or glycerol
10
Antifreeze proteins
ala
ala
thr

• Antifreeze glycoproteins (AFGPS)
• All have 3 amino acid repeats
• thr-ala-ala
• trimers make a helical repeat of just the right
  size.
• Stop development of ice crystals by binding to
  crystal edge!

11
Cool story of convergenceAntifreeze proteins in
arctic/antarctic fish
Arctic cods
Different superorders!
Antarctic nototheniods
Chen et al 1997 PNAS 94 3817-3822
12
AFGPs have different origins!
AFGPs modified from trypsinogen - a protease
produced by the pancreas! Now also produced by
liver
Antarctic nototheniods
Molecular clock suggests divergence of two genes
5-14 mya Antarctic ocean cooled to freezing
mid-Miocene 10-15 mya
????? Dont know where AFGP came from (but not
trypsinogen!)
Chen et al 1997 PNAS 94 3811 - 3816
13
This weeks IAB seminar
Antifreeze proteins and overwintering strategies
in insects
Jack Duman Notre Dame
Friday, 330 pm Elvey Auditorium
14
Homeothermic endothermyAnimals that bring the
heat
Who? Birds and mammals What? Maintain their
body temperature at a high, constant level Why?
Theyre always at Toptimum Where? All over
the globe, even in the coldest environments How?
Maintaining consistently high metabolic rates
15
True homeothermic endotherms are relatively rare
(lt 0.7 of species)
What Species Birds 9600 Mammals
4000 Everything else 1.8 - 2 million!
16
Endothermy evolved independently in birds and
mammals
Closest relatives of both endothermic lineages
are non-endotherms
17
Body temperarture in endotherms
Animal Normal core T Lethal core
T Monotreme 30-31 37 Marsupial 35-36 40-41 Eu
therian mammals 36-38 42-44 Birds,
non-passerine 39-40 46 Birds, passerine 40-41 4
7
primitive mammals
Endotherm Tb ranges about 10ºC lethal temp is
usually 6ºC above core
18
Why be a homeothermic endotherm?
19
Biological rates slow down with temperature
decreases
Rate of muscle contraction
As temperature drops, reaction rates slow
down This can be very Inconvenient!
Body temperature
20
At 35C
38C
38C
35C
21
At 10C
38C
38C
22
Endothermy Costs and Benefits

• BENEFITS
• Endotherms keep body at a constant, optimal body
  temperature
• Not at mercy of their environment)
• Always at thermal optimum
• COSTS
• Its metabolically very expensive
• Endotherms eat a lot more
• Enotherms require high rates of oxygen transport
• Theyre more active
• Burn more energy
• Produce more heat

23
Costs of endothermy

• Rate of energy consumption ( metabolic rate) of
  an endotherm is many times higher than that of a
  similarly sized ectotherm
• E.g. mouse MR 6-20X that of a similarly sized
  reptile
• It eats much more
• It has to counteract heat loss to a much greater
  extent
• Lower environmental temperatures more metabolic
  output

24
Metabolic rate vs. temperature - ENDOTHERM
Animal can maintain Tb w/o extra energy
Thermoneutral zone (TNZ)
Metabolic Rate (measured as oxygen
consumption rate ml O2/hr.)
Animal expends energy to stay warm
Animal expends energy to stay cool
Body temperature
50
5
15
25
35
45
0
Ambient temperature
25
Metabolic rate vs. temperature - ECTOTHERM
Metabolic Rate
Note for an ectotherm, being cold is CHEAPER!
For an endotherm, being cold is more expensive!
Body temperature
26
TNZ width can be variable
Pygmy possum TNZ 5-7ºC
Ptarmigan TNZ 35ºC
27
Depends on insulation (conductance)
28
Control of heat loss

• Insulation
• Feathers
• Fur
• Fat (blubber)
• Circulatory controls
• Vasodilation / vasoconstriction
• Countercurrent exchange

29
Controlling heat loss with reduced blood flow to
surface
COLD
WARM
heat flow
SKIN
Capillary bed
Capillary bed
arterial-venal anastomosis (shunt) OPEN
arterial-venal anastomosis (shunt) CLOSED
Vasodilation
Vasoconstriction
30
Thermoregulatory blood flow in humans
35ºC
20ºC
31
Control of peripheral perfusion

• Brain periodically sends messages to valves to
  open and perfuse capillary beds
• Raynaulds syndrome Brain forgets? Sticky
  valves?

32
Countercurrent exchange
(or, why dont birds lose all their body heat
through their feet?)
Brrrrr
33
Counter-current heat exchange
Cold Region 10
Hot Region 37
37 32 28 23 18 13
34 29 24 19 14 10
Counter current exchange Exchange of heat (or
other things) between two vessels that 1) run in
opposite directions 2) are in close
contact Simple but extremely effective!
34
Bird legs have countercurrent exchangers
Also mammal legs, Mammal noses Antlers (see
examples in book)
35
Anatomy of countercurrent exchange
artery
veins
2mm
Vein and artery arrangement in leg of a rook
36
Why dont their feet freeze?
3

• 1) Heat loss is low and constant until 0ºC
• 2) Below 0ºC blood flow speeds up
• countercurrent exchange is less efficient!
• 3) Birds pay higher energetic cost to keep feet
  slightly warm

2
1
37
Announcements

• Exam next week (Tuesday)!
• Will cover material through this Thursday
• Review session
• TODAY 730 9pm
• Irving 201 (This room)
• Additional OFFICE HOURS
• Thursday 1130 1230 2-4 p.m.
• Friday 9-10 a.m.
• Nikki Monday 1-230 pm
• Morgan ???