introduction to animal physiology homeostasis. physiology the study of the functions of living...
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Introduction to Animal Physiology
Homeostasis
Physiology
• The study of the functions of living organisms
– whole organisms
– organ systems
– organs
– tissues
– cells
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
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
tissues of the stomach wall
Figure 41.2
Table 41.1
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
homeostasis in a cellular suitcaseFigure 41.1
Homeostasis
• homeostatic regulatory components
– controlled systems - effectors
– regulatory systems
• acquire information
• process information
• integrate information
• send commands
Homeostasis
• homeostatic regulatory variables
– setpoint
• optimal chemical or physical condition
– feedback information
• actual current condition
– error signal
• discrepancy between setpoint and feedback value
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
the “responsible driver” exampleFigure 41.4
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 10˚C lower temperature
Q10 = RT / RT-10
biological range of Q10
values
Figure 41.5
Homeostasis: thermoregulation• acclimatization can alter an animal’s
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.)
acclimatization may
include metabolic
compensationFigure 41.6
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
Homeostasis: thermoregulation• animals are classified by how they respond to
environmental temperaturesand
• their sources (sinks) of body heat– ectotherm
• external heat sources/sinks– endotherm
• active heat generation and cooling
ectotherms and
endotherms utilize
different sources of body heat
Figure 41.7
behavioral temperature regulation in an ectotherm
Figure 41.8
Homeostasis: thermoregulation• behavior is a common method of regulating
body temperature– ectotherms
• different microenvironments provide different temperatures
– endotherms• behavioral temperature regulation reduces metabolic costs
behavioral temperature regulation in endothermsFigure 41.9
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
Figure 41.10
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
vegetarian marine iguanaFigure 41.11
an iguana regulates body temperature by altering heart rate in surf & sun
Figure 41.11
muscular contraction generates heat
brood warming by honey bees
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
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
a cold fish
dumps muscular
heatFigure 41.12
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
a hot fish
retains muscular
heatFigure 41.12
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
basal metabolic rate vs. body massFigure 41.13
endotherms regulate
body temperature
metabolicallyFigure 41.14
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
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
brown fat is
highly vascularized, has a high density of mitochondria,
and has smaller lipid dropletsFigure 41.15
reduced surface area
andincreased insulation conserve body heat
Figure 41.16
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
increased surface area andreduced insulation release body heat
Figure 41.16
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
a thermostat controls the effectors
(furnace and air conditioner) in a house
metabolic rate and
body temperature respond to hypothalamic temperature
changesFigure 41.17
ambient temperature(feedforward information)
can alter the
setpoint for
metabolic heat productionFigure 41.18
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
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
decreased metabolism, lower temperatureFigure 41.19