G. Metabolic Thermoregulation 4. How is body temperature maintained in wild?
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Transcript of G. Metabolic Thermoregulation 4. How is body temperature maintained in wild?
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G. Metabolic Thermoregulation
4. How is body temperature maintained in wild?
a. thermoreceptors in CNS, skin
b. hypothalamic set point
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c. If TB < set point, warm up
usually because TA < TB causes heat loss
(1) high BMR
(2) active heat production
Thermogenesis
shivering: asynchronous motor units
nonshivering: increase cellular calorigenesis
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These are E expensive
must be adapted to gain large amounts of E and O2
10 X intestinal surface area, 15 X lung surface area of ectotherms
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(3) cheaper alternative
adaptations to reduce heat loss
(a) Insulation
external pelage: fur or feathers
internal fat: blubber
(b) keep heat from environment by peripheral vasoconstriction: pale
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d. If TB > set point, cool down
occurs if TA > TB
also occurs if metabolic heat production increases
e.g. activity
insulation increases danger of overheating
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Cooling achieved by:
(1) passive heat loss: heat lost across skin by conductance
peripheral vasodilation: flushing
(2) active heat loss: increase mr to activate mechanisms to lose heat
evaporation
cutaneous water loss: sweating
respiratory water loss: panting
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Therefore, in endotherms:
at high temperatures: animal must work to cool
at low temperatures: animal must work to heat
in between, heat produced by BMR adequate to maintain TB
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e. Animal in trouble at extremes
(1) Hypothermia: heat loss exceeds maximum metabolic production
(2) Hyperthermia: heat gain exceeds maximum cooling capacity
Q10 effect becomes important
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5. Some animals well adapted to survive at extremes
a. Coldest environments for homeotherms
Polar terrestrial and aquatic
Adaptive strategy:
(1) conserve E rather than increase expenditure
Slope of curve depends on thermal conductivity across animal’s skin
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Ways to reduce thermal conductivity of skin
(a) improve pelage length and density to trap more air
(b) improve internal insulation with thick blubber
low thermal conductivity
low vascular supply
doesn’t require air to insulate
blood can bypass to shed heat if necessary
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(2) Large size reduces heat loss
(3) Alternatively, give up
(a) Hibernation:
prolonged regulation of TB 1° above TA
95% energy conservation
(b) Torpor:
brief drops in TB (overnight)
small mammals and birds
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b. Survival in hot environments
Limited to small range
(1) MR increases to support evaporation
Requires water vapor pressure gradient between animal and environment
Lung: 47 mm Hg H2O vapor
Hot, dry environments: 10-30 mm Hg
Hot, humid environments: reduce v.p. gradient
Hot, humid environments are stressful
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Rarely give up in hot environments
(2) Heat storage
large animals (camels) allow TB to increase during the day
returns to normal at night
Cool blood going to brain with inspired air
(3) Behavior: nocturnal, burrow
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7. Characteristics of Endotherms:
a. Big
b. Require lots of food and oxygen
c. Insulation
d. Sustained activity
e. Fast growth
f. Broad geographical range
All these describe dinosaurs
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IX. GAS TRANSPORT
A. Principles of Gas Supply and Exchange
1. Respiration: acquisition of O2 for aerobic metabolism
Diffusion is limited to 1 mm, so systems must exist for supply
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2. Pressure
Movement of gas is strictly a passive process
No active transport is used
Animals can't pump gas
a. Basic force:
Diffusion down pressure gradients
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b. Total atmospheric P at sea level, 20˚
760 mm Hg
c. Equals sum of partial pressures of all constituent gases
Each gas contributes in proportion to its % composition of air
e.g., O2 = 159 mm Hg
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N2
O2
Etc.
Clean Dry Air at Sea Level
% Composition
78%
20.9%
0.03%< 1%
CO2
593
159
0.23< 7
Partial Pressure(mm Hg)
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3. Factors can modify this pressure
a. Altitude
Increased altitude decreases total and partial pressures
b. Presence of other gases
Additional gases in air will displace oxygen
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(1) H2O vapor
all tissues are saturated with water
surrounded with water vapor
(a) water vapor displaces 02
(b) depending on “relative humidity”
air saturated with H2O vapor = 100% relative humidity
(c) ability of air to hold water vapor is temperature dependent
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N2
O2
CO2, Etc.
% Composition
73%
19.6%
6.2%
< 1%
555
149
47
< 9
Partial Pressure(mm Hg)
Displaces O2: Clean, moist air at sea level, 37°
H2O
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(2) CO2
(a) Produced by metabolism inside animal
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% Composition Partial Pressure(mm Hg)
N2
O2
Etc.
74.5%
13%
6.2%
< .3%
568
100
47
< 1
CO2
H2O6% 45
(b) Further displaces O2:Mammal lung, 37°, 100% r.h.
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4. Animals also concerned with gas concentrations
a. concentration = number of molecules/unit volume
b. In air, [O2] is high
e.g. at 24˚, 192 ml O2/L air
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c. Aquatic environments
[O2] is low
because solubility of O2 in water is low
O2 in air diffuses into water until pressures are equal
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159
0
pO2
c. Aquatic environments
[O2] is low
because solubility of O2 in water is low
O2 in air diffuses into water until pressures are equal
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159
0
c. Aquatic environments
[O2] is low
because solubility of O2 in water is low
O2 in air diffuses into water until pressures are equal
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159
159
c. Aquatic environments
[O2] is low
because solubility of O2 in water is low
O2 in air diffuses into water until pressures are equal
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159
159
[O2] = 192 ml/L
[O2] = 6.6 ml/L
pO2
c. Aquatic environments
[O2] is low
because solubility of O2 in water is low
O2 in air diffuses into water until pressures are equal
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d. [O2] also decreases with increasing T
760 mm, pO2=159, 15˚:
7.8 ml O2/L H2O
760 mm, pO2=159, 35˚:
5.0 ml O2/L H2O
Therefore, for aquatic environments, [O2] is low and temperature dependent
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B. Animals therefore exist in 2 distinct respiratory environments:
1. Terrestrial: air is respiratory medium
a. low viscosity and density
b. relatively high [O2]
c. rapid diffusion of gas: homogeneous
2. Aquatic: water is medium
a. high viscosity and density
b. relatively low [O2] (down to 0)
c. slow diffusion: heterogeneous
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C. Respiratory Transport Scheme
1. Sum of all gas transport mechanisms used in an animal
Reflects animal’s function as system to convert O2 to CO2
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External Internal
SKIN
TISSUES
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External Internal
pO2: 160 mm < 25 mm
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External Internal
pO2: 160 mm < 25 mm
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External Internal
pO2: 160 mm < 25 mm
pCO2: 0.2 mm up to 50 mm
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External Internal
pO2: 160 mm < 25 mm
pCO2: 0.2 mm up to 50 mm
O2 Gradient
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External Internal
pO2: 160 mm < 25 mm
pCO2: 0.2 mm up to 50 mm
O2 Gradient
CO2 Gradient
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C. Respiratory Transport Scheme
1. Sum of all gas transport mechanisms used in an animal
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2. Animals can still speed gas movement
a. Make it easy for gas to to cross membranes
b. Provide gas transport systems which facilitate diffusion
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3. Adaptations to facilitate diffusion
a. Specialized organ at interface of animal and medium
Respiratory Organ
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Respiratory Organ
< 25 mm
up to 50 mm
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b. Specialized internal transport mechanism to speed diffusion over distances
Blood
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up to 50 mm
< 25 mm
BLOOD
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c. Specialized mechanism in ECF to facilitate diffusion from blood to cells
Carrier Proteins
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up to 50 mm
< 25 mm
Carriers
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up to 50 mm
< 25 mm
D. Respiratory Organs
Carriers
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Generalized Structure of Respiratory Organs
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RESPIRATORYEPITHELIUM
Generalized Structure of Respiratory Organs
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MEDIUM
Generalized Structure of Respiratory Organs
ENVIRONMENT
High pO2
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MEDIUM
BLOOD
Generalized Structure of Respiratory Organs
High pO2
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MEDIUM
BLOOD
Generalized Structure of Respiratory Organs
High pO2
VASCULAR ENDOTHELIUM
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BLOOD
Generalized Structure of Respiratory Organs
ECF
MEDIUM
High pO2
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MEDIUM
High pO2
BLOOD
ECF
Generalized Structure of Respiratory Organs
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MEDIUM
BLOOD
Generalized Structure of Respiratory Organs
High pO2
High pCO2
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MEDIUM
BLOODHigh pCO2
Generalized Structure of Respiratory Organs
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1. Diffusion Rate of Gas
Governed by Fick Equation (1870)
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1. Diffusion Rate of Gas
Governed by Fick Equation (1870)
M =D A (PEXT - PINT)
L
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1. Diffusion Rate of Gas
Governed by Fick Equation (1870)
M =D A (PEXT - PINT)
L
Movement of gas/unit time (M) depends on:
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a. Permeability of epithelium to gas
D = Diffusion coefficient for given gas
L = Thickness of epithelium
Higher the permeability, more gas can cross
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Permeability is usually as high as possible because epithelium is thin (1-2 cells)
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Permeability is usually as high as possible because epithelium is thin (1-2 cells)
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b. Surface area of epithelium: A
Larger the epithelium, more gas can cross
Therefore, have very large respiratory organs
Lots of branching surfaces to increase surface area
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c. Pressure gradient across epithelium:
(PEXT-PINT)
Greater the difference in pressure between the medium and blood, the more gas diffuses
Animals work to maximize this gradient
Achieved by ventilation of epithelium
removes CO2
brings in new O2 at highest pressures
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E. Three Basic Types of Respiratory Organs
1. Lung
Medium is air
a. Structure:
bronchioles
alveoli
Blood 0.2 to 0.6 micrometers from air
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b. Fick Characteristics
Thin epithelia for permeability
Branching structure for large surface area
1 cc = 300 cm2
Ventilation insures gradient
“tidal” ventilation
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c. Lung/Terrestrial Breathing Advantages
(1) Air has high O2 content
(2) Low density makes air very cheap to breathe
only 1-2% of total E for ventilation
(3) Respiratory epithelium protected inside animal
immune system, filtration
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d. Disadvantages
(1) internal, so must keep moist and warm
inhale: humidify and heat air
exhale: release heat and water
(2) closed sac tends to trap CO2 and H2O at elevated pressures
reduces pO2 at epithelium from 160 to 100
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Can improve gas pressures
Birds
very high O2 demand
pump air through flow-through lung
flushes out CO2 (28 mm vs 45mm )
increases gradients for both O2 uptake and CO2 removal
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e. Control of lung ventilation
Medullary reflex arc
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Increased Blood pCO2
Decreased Blood O2
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Increased Blood pCO2
Decreased Blood O2
O2, CO2 Chemoreceptorsin Aortic and Carotid Bodies
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Increased Blood pCO2
Decreased Blood O2
O2, CO2 Chemoreceptorsin Aortic and Carotid Bodies
Medulla
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Increased Blood pCO2
Decreased Blood O2
O2, CO2 Chemoreceptorsin Aortic and Carotid Bodies
Medulla
Increase Ventilation Rate
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In terrestrial vertebrates
both O2 and CO2 being measured, but
CO2 of primary importance in ventilation control
low O2: inc. vent. rate 1.5 fold
high CO2: inc. vent. rate 10 fold
This reflex is extensively modified by
other blood chemistry characteristics
activity
muscle stretch
voluntary control