1. Physiology is the study of the functions of living organisms from cells to whole organisms and organ systems. 2. Homeostasis refers to maintaining a constant internal environment through controlled systems that acquire, process, and integrate information to regulate physical and chemical conditions. 3. Thermoregulation is one example of homeostasis, as animals regulate their body temperature through behaviors, anatomical adaptations, and metabolic processes to remain within a narrow viable range despite varying environmental temperatures.

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

5. tissues
of the stomach wall
Figure 41.2

6. Table 41.1

7. 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

8. homeostasis in a cellular suitcase
Figure 41.1

9. Homeostasis
• homeostatic regulatory components
–controlled systems - effectors
–regulatory systems
•acquire information
•process information
•integrate information
•send commands

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

11. 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

12. the “responsible driver” example
Figure 41.4

13. 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
Q = R / R

14. biological range
of
Q10
values
Figure 41.5

15. 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.)

16. acclimatization
may
include
metabolic
compensation
Figure 41.6

17. 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

18. 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

19. ectotherms
and
endotherms
utilize
different
sources of
body heat
Figure 41.7

20. behavioral temperature regulation in an
ectotherm
Figure 41.8

21. Homeostasis: thermoregulation
• behavior is a common method of regulating
body temperature
–ectotherms
•different microenvironments provide
different temperatures
–endotherms
•behavioral temperature regulation reduces
metabolic costs

22. behavioral temperature regulation in endotherms
Figure 41.9

23. 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

24. Figure 41.10

25. 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

26. vegetarian marine iguana
Figure 41.11

27. an iguana regulates body temperature by
altering heart rate in surf & sun
Figure 41.11

28. muscular contraction generates heat
brood warming by honey bees

29. 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

30. 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

31. a
cold
fish
dumps
muscular
heat
Figure 41.12

32. 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

33. a
hot
fish
retains
muscular
heat
Figure
41.12

34. 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

35. basal metabolic rate vs. body mass
Figure 41.13

36. endotherms
regulate
body
temperature
metabolically
Figure 41.14

37. 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

38. 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

39. brown fat
is
highly vascularized, has a
high density of mitochondria,
and has smaller
lipid droplets
Figure 41.15

40. reduced
surface area
and
increased
insulation
conserve
body heat
Figure 41.16

41. 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

42. increased surface area and
reduced insulation release body heat
Figure 41.16

43. 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

44. a thermostat controls the
effectors
(furnace and air conditioner)
in a house

45. metabolic
rate
and
body temperature respond
to hypothalamic temperature
changes
Figure 41.17

46. ambient temperature
(feedforward information)
can alter
the
setpoint
for
metabolic heat production
Figure 41.18

47. 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

48. 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

49. decreased metabolism, lower temperature
Figure 41.19