g. metabolic thermoregulation 4. how is body temperature maintained in wild?

17-1

G. Metabolic Thermoregulation

4. How is body temperature maintained in wild?

a. thermoreceptors in CNS, skin

b. hypothalamic set point

17-2

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

17-3

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

17-4

(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

17-5

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

17-6

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

17-7

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

17-8

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

17-9

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

17-10

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

17-11

(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

17-12

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

17-13

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

17-14

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

17-15

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

17-16

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

17-17

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

17-18

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)

17-19

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

17-20

(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

17-21

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

17-22

(2) CO2

(a) Produced by metabolism inside animal

17-23

% 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.

17-24

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

17-25

c. Aquatic environments

[O2] is low

because solubility of O2 in water is low

O2 in air diffuses into water until pressures are equal

17-26

159

0

pO2


[O2] is low



17-27

159

0


[O2] is low



17-28

159

159


[O2] is low



17-29

159

159

[O2] = 192 ml/L

[O2] = 6.6 ml/L

pO2


[O2] is low



17-30

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

17-31

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

17-32

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

17-34

External Internal

SKIN

TISSUES

17-35

External Internal

pO2: 160 mm < 25 mm

17-36

External Internal

pO2: 160 mm < 25 mm

17-37

External Internal

pO2: 160 mm < 25 mm

pCO2: 0.2 mm up to 50 mm

17-38

External Internal

pO2: 160 mm < 25 mm


O2 Gradient

17-39

External Internal

pO2: 160 mm < 25 mm


O2 Gradient

CO2 Gradient

17-40

C. Respiratory Transport Scheme

1. Sum of all gas transport mechanisms used in an animal

17-41

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

17-42

3. Adaptations to facilitate diffusion

a. Specialized organ at interface of animal and medium

Respiratory Organ

17-43

Respiratory Organ

< 25 mm

up to 50 mm

17-44

b. Specialized internal transport mechanism to speed diffusion over distances

Blood

17-45

up to 50 mm

< 25 mm

BLOOD

17-46

c. Specialized mechanism in ECF to facilitate diffusion from blood to cells

Carrier Proteins

17-47

up to 50 mm

< 25 mm

Carriers

17-48

up to 50 mm

< 25 mm

D. Respiratory Organs

Carriers

17-49

Generalized Structure of Respiratory Organs

17-50

RESPIRATORYEPITHELIUM


17-51

MEDIUM


ENVIRONMENT

High pO2

17-52

MEDIUM

BLOOD


High pO2

17-53

MEDIUM

BLOOD


High pO2

VASCULAR ENDOTHELIUM

17-54

BLOOD


ECF

MEDIUM

High pO2

17-55

MEDIUM

High pO2

BLOOD

ECF


17-56

MEDIUM

BLOOD


High pO2

High pCO2

17-57

MEDIUM

BLOODHigh pCO2


17-58

1. Diffusion Rate of Gas

Governed by Fick Equation (1870)

17-59



M =D A (PEXT - PINT)

L

17-60



M =D A (PEXT - PINT)

L

Movement of gas/unit time (M) depends on:

17-61

a. Permeability of epithelium to gas

D = Diffusion coefficient for given gas

L = Thickness of epithelium

Higher the permeability, more gas can cross

17-62

Permeability is usually as high as possible because epithelium is thin (1-2 cells)

17-63

Permeability is usually as high as possible because epithelium is thin (1-2 cells)

17-64

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

17-65

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

17-66

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

17-67

b. Fick Characteristics

Thin epithelia for permeability

Branching structure for large surface area

1 cc = 300 cm2

Ventilation insures gradient

“tidal” ventilation

17-68

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

17-69

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

17-70

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

17-71

e. Control of lung ventilation

Medullary reflex arc

17-72

Increased Blood pCO2

Decreased Blood O2

17-73


Decreased Blood O2

O2, CO2 Chemoreceptorsin Aortic and Carotid Bodies

17-74


Decreased Blood O2


Medulla

17-75


Decreased Blood O2


Medulla

Increase Ventilation Rate

17-76

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

g. metabolic thermoregulation 4. how is body temperature maintained in wild?

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