The Internal Environment
Maintaining Internal Balance
 Internal environment maintained in narrow range
 Homeostasis
 Extracellular fluid
 Interstitial—between cells of body tissues
 Blood
 Stays stable because of exchanges substances w/ environment
 Fluids & solutes enter by osmosis, digestive system,
metabolism
 Minerals & water lost through respiratory system, skin,
kidneys
Osmosis
 Diffusion—movement of substance
from high to low concentration
 Osmosis—diffusion of water across a
selectively permeable membrane
 Isotonic 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 Animals
 Mollusks, arthropods,
cartilaginous fish
 Body fluids nearly
isotonic to seawater
 No movement of salt or
water
 No difficulty maintaining
salt/water balance
Aquatic Animals
 Marine bony fish
 Seawater is hypertonic
 Prone to water loss
 Drink seawater constantly to
take in enough water
 Excess salt excreted by gills
 Scant, highly concentrated
urine retains water
Aquatic Animals
 Freshwater bony fish
 Freshwater is hypotonic
 Prone to water gain
 Never drink water
 Produce large amount of dilute
urine
 Must actively take salt through
gills and food
Land Animals
 Bigger risk of dehydration since not surrounded by
water
 Water gain—food, drink, metabolic reactions
 Water loss
 Do not loose through osmosis
 Urinary excretion
 Evaporation from respiratory surfaces
 Sweating in mammals
Land Animals
 Balance
 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 Waste
 Produced by breakdown of nucleic acids & amino
acids
 Ingestion
 Metabolic processes
 Ammonia produced
 Very toxic
 Must be eliminated
Nitrogen Waste
 Aquatic animals
 Excrete ammonia directly in urine
 Need large amounts of water
 Insects, reptiles, birds
 Excrete uric acid
 Low toxicity
 Poorly soluble in water


Therefore highly concentrated
Large amount of water conserved
 Mammals, terrestrial amphibians
 Excrete urea
 Less toxic than ammonia
 Excreted in moderately concentrated solution
Excretory Organs
 Flame cell
 Nematodes, platyhelminthes,
flatworms, rotifers
 Cilia in cells move water
through
 Tubules remove excess water
Excretory Organs
 Nephridium
 Many invertebrates,
mostly annelids
 Cilliated cells move fluid
from coelom into
nephridium
 Capillaries around tubule
reabsorbs solutes
 Dilute urine expelled
through external pore
Excretory Organs
 Malpighian tubules
 Insects, myriapods, arachnids
 Absorb water, solutes, wastes
from surrounding hemolymph
 Wastes excreted through gut
 Amount of fluid absorbed
dependent on environment
Excretory Organs
 Kidney
 Most vertebrates
 Filter blood
 Produce urine

Urea & uric acid
 Often other functions



Regulate blood pressure
Glucose metabolism
RBC production
Urinary System
 Kidneys
 Paired
 Cortex
 Medulla
 Pelvis

Only found in mammals
Urinary System
 Ureter—kidney to bladder
 Bladder—urine storage
 Only in mammals
 Urethra—bladder to outside
 Part of reproductive tract in
males
 Separate in females
Nephron
 Functional unit of
kidney
 Renal Corpuscle
 Non-selective filtration
 Glomerulus

Blood vessels enter
kidney
 Glomerular capsule

Filtrate collected
Nephron
 Renal 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
Nephron
 1 million nephrons in human kidney
 25% must be functional for homeostasis
 Maintain blood pH
 Release erythropoeitin for RBC production
 Stimulate ADH release when dehydrated
 Maintain blood pressure
 Chronic renal failure irreversible
 Dialysis—pump blood through machine that allows
diffusion of wastes, then pump blood back into body
Temperature Regulation
 Heat gain & loss
 Thermal radiation


Sun, warm object
Warmth produced by metabolism
 Conduction
 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 Regulation
 Heat 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 Regulation
 Cold stress
 Peripheral vasoconstriction
 Pilomotor response—hairs stand up


Layer of still air next to skin
Reduce convective and radiative heat loss
 Shivering


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