Lecture 25, 02 Dec 2003Chapter 15, Feeding and Digestion

Chapter 16, Energy Expenditure, Body Size

Vertebrate PhysiologyECOL 437

University of ArizonaFall 2003

instr: Kevin Boninet.a.: Bret Pasch

1

Vertebrate Physiology 437

1. Feeding and Digestion (CH15)

2. ~Energy Expenditure (CH16)

3. Announcements… - Term paper 04 Dec. - Seminar write-up 09 Dec. - Powerpoint (file to us on 09 Dec.) - Oral Presentations 10 Dec. (8min) - Movie and Thanksgiving Assgt due Wed - Read Ch17 for Thurs lecture - Friday Physiology Seminar (calcium regulation in endothelial cells)

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ABSORPTION:

-Across epithelium of brush border (microvilli)-Glycocalyx has enzymes for final cleavage disaccharidases, aminopeptidases, phosphatases-Simple Diffusion

1 fat-soluble substances2 small water soluble substances through

regulated aquaporins3 down concentration or electrochemical

gradients-Facilitated Diffusion

1 monosaccharides and amino acids2 transporter proteins3 down conc. gradient or4 coupled to Na+ gradient (Na/K-

ATPase)

3

(15-37)

4

ABSORPTION

-Active Transport-amino acids with ~specific

transporters coupled to Na+-Lipids

-products cross into epithelial cells (monoglycerides, fatty acids,

glycerol)-reconstructed into triglycerides-formed into chylomicrons using

cholesterol and phospholipids-chylomicrons exocytosed-taken into central lacteal and into

lymph system

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(15-38)

Lipids6

ER

Golgi

Lacteal

Nutrient Transport in Blood

-lipids (chylomicrons) into blood from lymph at thoracic duct

-sugars and amino acids into capillaries of villi-to liver via hepatic portal vein

sugars converted to glycogen for storage

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Water and Electrolyte Balance in Gut

-Lots of water and electrolytes secreted into lumen

-Need to recover

-Most via lower small intestine (ileum)-Osmotic gradient b/c absorb salts, carbos, amino acids

-Tips of villi

-Countercurrent exchange with high Na+ (Cl- follows) to facilitate water reabsorption

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(15-39)

Secretions etc.

=

9

ileum

Nu

trit

ional R

eq

uir

em

ents

… (

Ess

enti

al?

)

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Chapter 16

Energy Expenditure-temperature-size-activity

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Metabolism

-Chemical reactions in the body-Temperature dependent rates-Not 100% efficient, energy lost as heat

(not ‘lost’ if used to maintain Tb)

1. Anabolic-creation, assembly, repair, growth (positive nitrogen balance)

2. Catabolic-energy release from complex molecules (carbos, fats, proteins)-energy storage in phosphate bonds (ATP) and metabolic intermediates (glucose, lactate)

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Chemical Energy

(16-1)

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Metabolic Rate

-measurable conversion of chemical energy into heat

-used to understand:-energy budgets-dietary needs-body size implications-habitat effects-costs of various activities-mode of locomotion-cost of reproduction

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Metabolic Rates

-Basal Metabolic Rate, BMR-minimal environmental and physiological

stress (appropriate ambient temperature, post-digestive, resting etc.)

-Standard Metabolic Rate, SMR-similar to BMR, but at a given Tb

-Field Metabolic Rate, FMR-average metabolic rate of animal in natural

setting-hard to measure

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Metabolic Rates

Basal Metabolic Rate, BMR-important components:

1. Membrane form and functionmaintenance of electrochemical gradients-proton pumps in mitochondrial membranes-Na/K-ATPase pumps in plasma membrane

2. Protein synthesis

3. ATP formation

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Specific Dynamic Action (SDA)

-Metabolic Rate increases during digestion-2-3x resting metabolism in ectotherms

Think about infrequently feeding snakes...

(16-5)

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Measuring Metabolism

Direct Calorimetry-measure heat produced-known mass of water surrounding chamber-not often used (maybe for small birds,

mammals)Indirect Calorimetry

1. Bomb calorimetry (food and waste)

2. Radioisotopesdeuterium or tritium (H3) labelled wateroxygen radioisotopes (O18)(doubly-labelled water)

-measure loss of CO2 and water over time-can be used in the field-measure metabolism and water flux

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4kJ = 1kcal

Power (W)=J/s

Measuring Metabolism

Respirometry-measure O2 consumption and CO2

production-assumes primarily aerobic metabolism-closed vs. open

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4kJ = 1kcal

Power (W)=J/s

(16-3)

gills

lungs

skin

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RQ, Respiratory Quotient

RQ = Rate of CO2 production

Rate of O2 consumption

Value depends on substrate oxidized:

Energy Storage

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4kJ = 1kcal

Power (W)=J/s

RE, Respiratory Exchange Ratio

RE = instantaneous ratio of O2 consumption and CO2 production

(16-4)

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Metabolic Scope

Aerobic Metabolic Scope= max sustainable metabolic rate / BMR

-usually measured as O2 consumption-often = 10-15 x BMR-does not include anaerobic contributions-best measured at steady-state, sustainable levels

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Aerobic ScopeMammal MAS (max aerobic speed)

7.5x that of Lizard MAS (of similar body size)

Anaerobic ScopeMammal and Lizard maximal speed

equivalent at a given body mass

-ecological implications?

-both tend to increase with increasing body mass

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(16-2)

Oxygen Debt-repay anaerobic contribution to elevated

metabolism-oxidize anaerobic products (e.g., lactate)

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VO2 Measurement - Before, during, and after exercise

Thomas Hancock: data and slides

Desert Iguana

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VO

2

Time (min)

0 15 30 45

EXERCISE RECOVERY

EPOC: Excess Post-exercise Oxygen Consumption

Activity and Associated Oxygen Consumption

EEOC: Excess Exercise Oxygen Consumption

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VO

2

Time (min)

0 15 30 45

EXERCISE RECOVERY

EPOC

EEOC

TEOC = Total Excess Oxygen Consumption = EEOC + EPOC

Activity and Associated Oxygen Consumption28

Muscle Lactate

0

10

20

30

40

50

Lac

tate

(m

M)

0 2 4 6 8 10 12 14 16

Recovery Time (min)

WIF

RIF

Gastrocnemius

60

Exercise,

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Energy Budget Implications

Costs for Exercise and Recovery:- A Single Bout: 15 seconds at Maximum intensity

• Traditional Estimates: 0.7% of daily energy expenditure

• Inclusion of EPOC:4.6% of daily energy expenditure

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VO

2

Time (min)

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Length of Bout is Important:

VO

2

Time (min)

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VO

2

Time (min)

33

VO

2

Time (min)

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VO

2

Time (min)

EPOC is now a large fraction of the net metabolic expenditure.

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Phylogenetic Effects

FMR (kJ/day)

(Nagy, Girard, Brown 1999)

100g mammal

100g reptile

100g bird

11.8

142

242

Energy Budgets…Ecological Role…

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Scaling Effects

Allometry - changes in body proportions as animals get larger (mouse vs. elephant)

Metabolic Rate - mass-specific metabolic rate decreases with increasing body mass

(16-6)

linear

squared

cubed

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Knut Schmidt_Nielsen 1972

(a) = elephant freaked out and died (1960’s)

-What is the correct dose?

-Importance of Scaling!

0.1mg/kg

0.2mg for 70 kg

(16-8)

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Scaling

Power Functions:

How do morphology and metabolism change with body mass?

MR = aMb

Metabolicrate

Y-intercept (of log-log plot)

Body mass

Scaling exponent

logMR = loga + b(logM)

Can look at mass-specific rates by dividing through by M

Take log of both sides

(Linearizes)

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(16-8)

MR = aMbb = 0.75(slope) logMR = loga +

b(logM)

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(16-7)

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END

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