Chapter 44:Chapter 44:Maintaining a Constant Maintaining a Constant Internal Environment Internal Environment

(Homeostasis)(Homeostasis)

Body TemperatureBody Temperature Enzymes: Rxn rates inc. 2-3 Enzymes: Rxn rates inc. 2-3

times with each 10times with each 1000 C temp. inc. C temp. inc. (until denatured)(until denatured)

Each species has an optimal Each species has an optimal temp. range for metabolic rxns to temp. range for metabolic rxns to be efficientbe efficient

ThermoregulationThermoregulation Organisms Organisms maintain their body temp within maintain their body temp within optimal range (various methods)optimal range (various methods)

Heat Gain/LossHeat Gain/Loss

Heat Gain/Loss (HIGH to LOW)Heat Gain/Loss (HIGH to LOW) ConductionConduction = molecule to molecule = molecule to molecule

(ie: hot concrete and feet in summer)(ie: hot concrete and feet in summer) ConvectionConvection = heat transfer b/t object = heat transfer b/t object

and Hand H22O or air moving across itO or air moving across it RadiationRadiation = electromagnetic waves = electromagnetic waves

transferred as heat (ie: suns rays)transferred as heat (ie: suns rays) Evaporative CoolingEvaporative Cooling = lowers temp = lowers temp

by releasing Hby releasing H22O as vapor (ie: O as vapor (ie: sweating)sweating)

Ectotherms and EndothermsEctotherms and Endotherms EctothermsEctotherms (“cold-blooded”) maintain a (“cold-blooded”) maintain a

temperature close to external temp.temperature close to external temp.•Low metabolic requirements (little heat Low metabolic requirements (little heat

generated)generated)•Most fish, reptiles, amphibians Most fish, reptiles, amphibians

EndothermsEndotherms (“warm-blooded”) maintain (“warm-blooded”) maintain a constant temp. that may vary a constant temp. that may vary significantly from external temp (species significantly from external temp (species dependent)dependent)•High metabolic rate (lots of heat!)High metabolic rate (lots of heat!)•Humans, other mammals, and birdsHumans, other mammals, and birds

Endotherms/EctothermsEndotherms/Ectotherms

Endothermic AdvantagesEndothermic Advantages Higher temp allows for inc. metabolic Higher temp allows for inc. metabolic

raterate More energy is generatedMore energy is generated Can perform more vigorous activities Can perform more vigorous activities

for more sustained periodsfor more sustained periods Allows terrestrial life (more temp. Allows terrestrial life (more temp.

fluctuations than Hfluctuations than H22O)O) Disadvantage : Require more Disadvantage : Require more

frequent meals for higher aerobic frequent meals for higher aerobic resp. rateresp. rate

Vasodilation and VasoconstrictionVasodilation and Vasoconstriction VasodilationVasodilation Blood vessels Blood vessels

dilate (expand) in order to dilate (expand) in order to release more heatrelease more heat

VasoconstrictionVasoconstriction Blood vessels Blood vessels constrict in order to limit heat constrict in order to limit heat loss in the coldloss in the cold

Behavioral ControlsBehavioral Controls Basking in the sun to raise body Basking in the sun to raise body

temptemp HibernationHibernation Migration to different climates Migration to different climates

(birds)(birds) Inc or dec metabolic rate in Inc or dec metabolic rate in

hot/cold tempshot/cold temps Certain insects huddle to Certain insects huddle to

generate more heatgenerate more heat

InsulationInsulation HairHair FeathersFeathers Blubber, fatBlubber, fat Reduces the loss of heatReduces the loss of heat Allows maintenance of higher Allows maintenance of higher

body tempsbody temps

InsulationInsulation

Thermoregulation in HumansThermoregulation in Humans

Thermoregulation in HumansThermoregulation in Humans Heat receptors in skinHeat receptors in skin

Receptors send hot/cold signal to Receptors send hot/cold signal to hypothalamus (brain)hypothalamus (brain)

Hypothalamus regulates Hypothalamus regulates vasodilation and vasoconstrictionvasodilation and vasoconstriction

Extreme Hot/Cold EnvironmentsExtreme Hot/Cold Environments

CryoprotectantsCryoprotectants Certain Certain organisms (some frog eggs, organisms (some frog eggs, arctic fish) have a biologically arctic fish) have a biologically produced antifreezeproduced antifreeze

Heat shock proteinsHeat shock proteins Produced Produced in response to heat. Bind to in response to heat. Bind to enzymes and other proteins to enzymes and other proteins to inhibit denaturizationinhibit denaturization

HibernationHibernation

Bears, squirrels go into a Bears, squirrels go into a deep sleep during winter in deep sleep during winter in order to avoid harsh order to avoid harsh conditionsconditions

Very low energy demandsVery low energy demands Very low metabolic rateVery low metabolic rate

HibernationHibernation

Osmoregulation (Water Balance)Osmoregulation (Water Balance) Organisms must balance their Organisms must balance their

water and solute concentrationswater and solute concentrations Water uptake and loss must Water uptake and loss must

remain essentially equalremain essentially equal Cells could swell or shrivelCells could swell or shrivel Water flows from high water Water flows from high water

potential (low [solute]) to low potential (low [solute]) to low water potential (high [solute])water potential (high [solute])

Osmoregulators/OsmoconformorsOsmoregulators/Osmoconformors OsmoregulatorsOsmoregulators maintain a constant maintain a constant

solute concentration different from solute concentration different from that of ext. environmentthat of ext. environment•Freshwater, terrestrial, some Freshwater, terrestrial, some

marine marine •Costs energy (active transport)Costs energy (active transport)

OsmoconformersOsmoconformers maintain solute maintain solute concentration equal to that of concentration equal to that of surroundingssurroundings•Many marine invertebratesMany marine invertebrates

OsmoregulationOsmoregulation

Waste DisposalWaste Disposal Elimination of toxic materials is needed Elimination of toxic materials is needed

to maintain homeostasisto maintain homeostasis Nitrogenous wastes are very toxic to Nitrogenous wastes are very toxic to

living cellsliving cells•UreaUrea Many terrestrial organisms, Many terrestrial organisms,

lowest toxicity, high energy lowest toxicity, high energy requirement (humans)requirement (humans)

•Uric AcidUric Acid Birds, insects reptiles, Birds, insects reptiles, least water lostleast water lost

•AmmoniaAmmonia Fish, aquatic organisms, Fish, aquatic organisms, most toxicmost toxic

Nitrogenous WasteNitrogenous Waste

Selective Reabsorption and SecretionSelective Reabsorption and Secretion Organisms will filter Organisms will filter

their wastes and their wastes and reabsorb anything reabsorb anything that may be of use that may be of use

Accomplished in Accomplished in tubules (present in tubules (present in human kidneys)human kidneys)

May also secrete May also secrete more waste more waste materials into urinematerials into urine

Malpighian TubulesMalpighian Tubules

Remove nitrogenous wastes from open circulatory system of insects

Vertebrate Urinary SystemVertebrate Urinary System KidneysKidneys

•Function in osmoregulation and Function in osmoregulation and reabsorptionreabsorption

•Contain a network of tubulesContain a network of tubules Renal ArteryRenal Artery Blood to kidney Blood to kidney Renal VeinRenal Vein Blood from kidney Blood from kidney UreterUreter Carries urine to bladder Carries urine to bladder BladderBladder Stores urine Stores urine UrethraUrethra Tube that exits the body Tube that exits the body

Vertebrate KidneysVertebrate Kidneys Two regionsTwo regions

•Renal cortex and renal medullaRenal cortex and renal medulla Contains millions of Contains millions of nephronsnephrons

•Microscopic tubulesMicroscopic tubules GlomerulusGlomerulus Network of Network of

capillaries serving each nephron capillaries serving each nephron with a blood supplywith a blood supply

Bowman’s CapsuleBowman’s Capsule End of tubule End of tubule that surrounds the glomerulus that surrounds the glomerulus

Human KidneyHuman Kidney

KidneysKidneys

nephron and collecting duct are lined nephron and collecting duct are lined by a transport epithelium by a transport epithelium

process filtrate to form urine process filtrate to form urine reabsorb solutes and waterreabsorb solutes and water

•sugar, vitamins, and other organic sugar, vitamins, and other organic nutrients from the initial filtrate nutrients from the initial filtrate and about 99% of the waterand about 99% of the water

reduce 180 L of initial filtrate to reduce 180 L of initial filtrate to about 1.5 L of urine to be voidedabout 1.5 L of urine to be voided

Kidney FunctionKidney Function Proximal TubuleProximal Tubule NaCl and H NaCl and H22O O

reabsorption and pH regulationreabsorption and pH regulation Descending Loop of HenleDescending Loop of Henle H H22O O

reabsorptionreabsorption Ascending Loop of HenleAscending Loop of Henle NaCl NaCl

reabsorptionreabsorption Distal TubuleDistal Tubule K K++ and NaCl balance, and NaCl balance,

pH regulation, some HpH regulation, some H22O reabsorbedO reabsorbed Collecting DuctCollecting Duct NaCl reabsorption, NaCl reabsorption,

HH22O reabsorptionO reabsorption As it moves through the kidney, urine As it moves through the kidney, urine

becomes more concentrated with becomes more concentrated with unusable wasteunusable waste

KidneysKidneys

Kidneys give terrestrial Kidneys give terrestrial vertebrates the ability to vertebrates the ability to regulate their osmotic regulate their osmotic balancebalance

Without kidneys, life on land Without kidneys, life on land would not be possiblewould not be possible