Introduction to Animal Physiology

1
Introduction to Animal Physiology

• Homeostasis

2
Physiology

• The study of the functions of living organisms
• whole organisms
• organ systems
• organs
• tissues
• cells

3
Physiology

• groups of cells with similar characteristics or
  specializations form tissues
• different tissues combine to form organs
• discrete structures with specific functions
• organs which function together form organ systems

4
Physiology

• tissues occur in four basic types
• epithelial tissues form linings or coverings
• perform functions appropriate to organ
• connective tissues exist in a matrix
• support and reinforce other tissues
• muscle tissues contract
• provide movement or propulsion
• nervous tissues transmit and process information

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tissues of the stomach wallFigure 41.2
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Table 41.1
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Homeostasis

• most organ systems contribute to homeostasis
• maintenance of a constant internal environment in
  spite of constant change
• provides for material needs of cells
• removes wastes from cells
• regulates physical environment of cells
• communicates among cells

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homeostasis in a cellular suitcaseFigure 41.1
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Homeostasis

• homeostatic regulatory components
• controlled systems - effectors
• regulatory systems
• acquire information
• process information
• integrate information
• send commands

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Homeostasis

• homeostatic regulatory variables
• setpoint
• optimal chemical or physical condition
• feedback information
• actual current condition
• error signal
• discrepancy between setpoint and feedback value

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Homeostasis

• homeostatic regulatory inputs
• negative feedback
• reduces or reverses activity of effector
• returns condition to set point
• positive feedback
• amplifies activity of effector
• self-limiting activities
• feedforward information
• changes setpoint

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the responsible driver exampleFigure 41.4
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Homeostasis thermoregulation

• living cells cannot survive temperatures above or
  below fairly narrow limits
• thermosensitivities of organisms vary
• thermosensitivities of effectors vary
• Q10 quantifies temperature sensitivity
• ratio of physiological rate at one temperature to
  the rate at 10C lower temperature
• Q10 RT / RT-10

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Figure 41.5
biological range of Q10values
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Homeostasis thermoregulation

• acclimatization can alter an animals temperature
  response
• changes that allow optimal activity under
  different climatic conditions e.g. seasonal
  temperature variation
• metabolic compensation
• maintains metabolic rate in different seasons
• accomplished with alternate enzyme systems (e.g.)

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acclimatization may include metabolic
compensationFigure 41.6
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Homeostasis thermoregulation

• animals are classified by how they respond to
  environmental temperatures
• homeotherm
• maintains a constant body temperature as ambient
  temperature changes
• poikilotherm
• changes body temperature as ambient temperature
  changes

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Homeostasis thermoregulation

• animals are classified by how they respond to
  environmental temperatures
• and
• their sources (sinks) of body heat
• ectotherm
• external heat sources/sinks
• endotherm
• active heat generation and cooling

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ectotherms and endotherms utilize different
sources of body heatFigure 41.7
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behavioral temperature regulation in an
ectothermFigure 41.8
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Homeostasis thermoregulation

• behavior is a common method of regulating body
  temperature
• ectotherms
• different microenvironments provide different
  temperatures
• endotherms
• behavioral temperature regulation reduces
  metabolic costs

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behavioral temperature regulation in
endothermsFigure 41.9
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Homeostasis thermoregulation

• heat exchange between body and environment occurs
  through the skin
• radiation - gain or loss
• conduction - gain or loss
• convection - gain or loss
• evaporation - loss

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Figure 41.10
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Homeostasis thermoregulation

• heat exchange can be regulated by control of
  blood flow to the skin
• constriction/dilation of blood vessels supplying
  the skin
• change in heart rate

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vegetarian marine iguanaFigure 41.11
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an iguana regulates body temperature by altering
heart rate in surf sunFigure 41.11
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muscular contraction generates heat brood
warming by honey bees
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Homeostasis thermoregulation

• some ectotherms use muscular contractions to
  generate heat
• insects flex wing muscles
• to achieve flight temperature
• to warm brood above air temperature
• Indian python flexes muscles to warm brood above
  air temperature
• analogous to mammalian shivering

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Homeostasis thermoregulation

• anatomical features allow some fish to retain
  muscular heat
• in cold fish
• blood is chilled in gills
• cold blood is warmed by muscle mass
• warmed blood returns to gills and is chilled

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a cold fish dumps muscular heatFigure 41.12
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Homeostasis thermoregulation

• anatomical features allow some fish to retain
  muscular heat
• in hot fish
• chilled blood from gills travels near skin
• chilled blood enters muscle mass next to veins
  leaving muscle mass
• countercurrent heat exchange warms blood entering
  muscle mass
• countercurrent heat exchange removes heat from
  blood returning to the gills

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a hot fish retains muscular heatFigure 41.12
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Homeostasis thermoregulation

• thermal characteristics of endotherms
• thermoneutral zone
• temperature window with no regulation
• basal metabolic rate
• meets minimal metabolic needs
• lower critical temperature
• below which metabolic rate increases
• upper critical temperature
• above which active cooling occurs

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basal metabolic rate vs. body massFigure 41.13
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endotherms regulate body temperature
metabolicallyFigure 41.14
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Homeostasis thermoregulation

• thermal characteristics of endotherms
• heat generation below the lower critical
  temperature
• shivering heat production
• contractions of opposed muscles
• releases heat from ATP hydrolysis

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Homeostasis thermoregulation

• thermal characteristics of endotherms
• heat generation below the lower critical
  temperature
• nonshivering heat production
• occurs in brown fat tissue
• due to thermogenin
• uncouples respiratory electron transport from ATP
  synthesis

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brown fat is highly vascularized, has a high
density of mitochondria, and has smaller lipid
dropletsFigure 41.15
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reduced surface area andincreased insulation
conserve body heatFigure 41.16
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Homeostasis thermoregulation

• thermal characteristics of endotherms
• anatomical features conserve heat below the lower
  critical temperature
• reduced surface/volume ratio
• increased thermal insulation
• oil secretion resists wetting

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increased surface area andreduced insulation
release body heatFigure 41.16
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Homeostasis thermoregulation

• thermal characteristics of endotherms
• heat loss above the upper critical temperature
• increased surface area/volume ratio
• increased blood flow to skin
• evaporation
• sweat glands
• panting

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a thermostat controls the effectors (furnace
and air conditioner) in a house
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metabolic rate and body temperature respond
to hypothalamic temperature changesFigure 41.17
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ambient temperature(feedforward information)can
alter the setpoint for metabolic heat
productionFigure 41.18
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Homeostasis thermoregulation

• mammalian thermal regulation
• the mammalian thermostat is the hypothalamus
• different effectors of thermal regulation have
  different set points
• environmental temperature can act as feed forward
  information to alter set points
• pyrogens increase the set point for metabolic
  heat production causing fever

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Homeostasis thermoregulation

• torpor conserves metabolic resources
• torpor is regulated hypothermia
• some birds engage in daily torpor during inactive
  periods
• in hibernating mammals, torpor may last hours,
  days, or weeks

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decreased metabolism, lower temperatureFigure
41.19