lecture 25, 02 dec 2003 chapter 15, feeding and digestion chapter 16, energy expenditure, body size...

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)

2

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

5

(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

7

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

8

(15-39)

Secretions etc.

=

9

ileum

Nu

trit

ional R

eq

uir

em

ents

… (

Ess

enti

al?

)

10

Chapter 16

Energy Expenditure-temperature-size-activity

11

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)

12

Chemical Energy

(16-1)

13

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

14

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

15

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

16

Specific Dynamic Action (SDA)

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

Think about infrequently feeding snakes...

(16-5)

17

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

18

4kJ = 1kcal

Power (W)=J/s

Measuring Metabolism

Respirometry-measure O2 consumption and CO2

production-assumes primarily aerobic metabolism-closed vs. open

19

4kJ = 1kcal

Power (W)=J/s

(16-3)

gills

lungs

skin

20

RQ, Respiratory Quotient

RQ = Rate of CO2 production

Rate of O2 consumption

Value depends on substrate oxidized:

Energy Storage

21

4kJ = 1kcal

Power (W)=J/s

RE, Respiratory Exchange Ratio

RE = instantaneous ratio of O2 consumption and CO2 production

(16-4)

22

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

23

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

24

(16-2)

Oxygen Debt-repay anaerobic contribution to elevated

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

25

VO2 Measurement - Before, during, and after exercise

Thomas Hancock: data and slides

Desert Iguana

26

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

27

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,

29

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

30

VO

2

Time (min)

31

Length of Bout is Important:

VO

2

Time (min)

32

VO

2

Time (min)

33

VO

2

Time (min)

34

VO

2

Time (min)

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

35

Phylogenetic Effects

FMR (kJ/day)

(Nagy, Girard, Brown 1999)

100g mammal

100g reptile

100g bird

11.8

142

242

Energy Budgets…Ecological Role…

36

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

37

38

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)

39

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)

40

(16-8)

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

b(logM)

41

(16-7)

42

END

xx