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 suitcase Figure 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” example Figure 41.4

Homeostasis: thermoregulation living cells cannot survive temperatures above or below fairly narrow limits –thermosensitivities of organisms vary –thermosensitivities of effectors vary Q 10 quantifies temperature sensitivity –ratio of physiological rate at one temperature to the rate at 10˚C lower temperature Q 10 = R T / R T-10

biological range of Q 10 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 compensation Figure 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 temperatures and 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 endotherms Figure 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 iguana Figure 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 heat Figure 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 heat Figure 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 mass Figure 41.13

endotherms regulate body temperature metabolically Figure 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 droplets Figure 41.15

reduced surface area and increased 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 and reduced 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 changes Figure 41.17

ambient temperature (feedforward information) can alter the setpoint for metabolic heat production Figure 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 temperature Figure 41.19