Chapter 42The Internal Environment

Maintaining Internal BalanceInternal environment maintained in narrow range

HomeostasisExtracellular fluid

Interstitial—between cells of body tissuesBloodStays stable because of exchanges substances w/

environmentFluids & solutes enter by osmosis, digestive

system, metabolismMinerals & water lost through respiratory

system, skin, kidneys

OsmosisDiffusion—movement of substance

from high to low concentrationOsmosis—diffusion of water

across a selectively permeable membraneIsotonic solution—concentration

of solutes equal in and out of cell, no net movement of water

Hypertonic solution—concentration of solutes greater outside of cell than inside; water moves out of cell

Hypotonic—concentration of solutes greater inside of cell than outside; water moves into cell

Aquatic AnimalsMollusks, arthropods,

cartilaginous fishBody fluids nearly

isotonic to seawaterNo movement of salt

or waterNo difficulty

maintaining salt/water balance

Aquatic AnimalsMarine bony fish

Seawater is hypertonicProne to water lossDrink seawater constantly

to take in enough waterExcess salt excreted by

gillsScant, highly concentrated

urine retains water

Aquatic AnimalsFreshwater bony fish

Freshwater is hypotonicProne to water gainNever drink waterProduce large amount of

dilute urineMust actively take salt

through gills and food

Land AnimalsBigger risk of dehydration since not

surrounded by waterWater gain—food, drink, metabolic reactionsWater loss

Do not loose through osmosisUrinary excretionEvaporation from respiratory surfacesSweating in mammals

Land AnimalsBalance

Birds & reptiles have glands to eliminate salt Marine iguanas specialized

Reptiles dry, scaly skin to prevent water loss

Desert mammals (camel, kangaroo rat, etc.) Reabsorb moisture from exhaled air Limited amount of urine, highly

concentrated No sweat glands More absorption of water from

feces More active in cooler parts of day

Nitrogen WasteProduced by breakdown of nucleic acids &

amino acidsIngestionMetabolic processes

Ammonia producedVery toxic Must be eliminated

Nitrogen WasteAquatic animals

Excrete ammonia directly in urineNeed large amounts of water

Insects, reptiles, birdsExcrete uric acidLow toxicityPoorly soluble in water

Therefore highly concentrated Large amount of water conserved

Mammals, terrestrial amphibiansExcrete ureaLess toxic than ammoniaExcreted in moderately concentrated solution

Excretory OrgansFlame cell

Nematodes, platyhelminthes, flatworms, rotifers

Cilia in cells move water through

Tubules remove excess water

Excretory OrgansNephridium

Many invertebrates, mostly annelids

Cilliated cells move fluid from coelom into nephridium

Capillaries around tubule reabsorbs solutes

Dilute urine expelled through external pore

Excretory OrgansMalpighian tubules

Insects, myriapods, arachnids

Absorb water, solutes, wastes from surrounding hemolymph

Wastes excreted through gut

Amount of fluid absorbed dependent on environment

Excretory OrgansKidney

Most vertebratesFilter blood Produce urine

Urea & uric acidOften other functions

Regulate blood pressure Glucose metabolism RBC production

Urinary SystemKidneys

PairedCortexMedullaPelvis

Only found in mammals

Urinary SystemUreter—kidney to bladderBladder—urine storage

Only in mammalsUrethra—bladder to

outsidePart of reproductive tract

in malesSeparate in females

NephronFunctional unit of

kidneyRenal Corpuscle

Non-selective filtration

Glomerulus Blood vessels enter

kidneyGlomerular

capsule Filtrate collected

NephronRenal Tubules

99% of filtered products reabsorbed

Proximal convoluted tubule Organic Solutes (amino acids,

glucose) 2/3 of salt & water

Loop of Henle Concentrates salt (absorbs

water)Distal convoluted tubule

Reabsorb calcium, excrete potassium

Nephron1 million nephrons in human kidney25% must be functional for homeostasis

Maintain blood pHRelease erythropoeitin for RBC productionStimulate ADH release when dehydratedMaintain blood pressure

Chronic renal failure irreversibleDialysis—pump blood through machine that

allows diffusion of wastes, then pump blood back into body

Temperature RegulationHeat gain & loss

Thermal radiation Sun, warm object Warmth produced by

metabolismConduction

Transferred between two objects in direct contact

Convection Moving air or water “Wind chill”

Evaporation Water on surface converts to

gas Draws heat from body

Temperature RegulationHeat stress

Peripheral vasodilation—diameter of skin blood vessels increases

Evaporation Sweat—most mammals, no other

animals Licking fur Panting

Move to shaded, cooled area Under surface of ground, rocks

Design adaptations Desert animals usually smaller

(greater surface area per body size), less body fat, thinner hair coats

Temperature RegulationCold stress

Peripheral vasoconstrictionPilomotor response—hairs stand up

Layer of still air next to skin Reduce convective and radiative heat

lossShivering

Muscles contract 10-20x per second Generates internal heat

Nonshivering heat production Long-term (hibernating animals) Brown adipose tissue

Move to warmer area Reptile basking

Design adaptations Thicker coat, larger size (smaller surface

area), increased fat for insulation