CHAPTER 44

CONTROLLING THE INTERNAL ENVIRONMENT

I. Cells require a balance between water uptake & loss

• Animal cells cannot survive a net gain or loss of water

• Solutes in blood ensure proper water balance in cells

A. How it is balanced

1. osmoconformers: do not actively adjust their internal osmolarity

(ex: salt water animals – body fluids are isotonic)

2. osmoregulators: animals that regulate internal osmolarity by discharging excess water or taking in water (expends energy)

• Large changes = usually fatal (stenohaline)

euryhaline can survive

B. Maintaining water balance in different environments

• Most marine invertebrates – osmoconformers

• Sharks = pump salt out

• Marine bony fish = hypotonic (excrete little urine)

• Freshwater

protozoa – contractile vacuole

fish = large amounts of dilute urine

• Terrestrial animals:

protective outer layers (shells, skin)

drinking & eating moist food

behavior (nocturnal)

excretory organs

II. Tubular systems function in osmoregulation & excretion in

many invertebrates

A. Protonephridia in Flatworms:

- network of closed tubules lacking internal openings that branch thru body

B. Metanephridia in Earthworms

- each segment – pair of meta.

- excretory tubules that have internal openings to collect body fluids

C. Malpighian Tubules in Insects

- remove nitrogenous wastes from hemolymph

III. The kidneys of most vertebrates are compact organs

with many excretory tubules

A. The Mammalian Excretory System

* bean-shaped organs in back

* renal artery – kidney – renal vein (blood flow)

* urine out kidney – ureter – bladder – urethra (urine flow)

B. The Nephron & Associated Structures

• 2 distinct regions: outer renal cortex & inner renal medulla (each w/ nephrons * collecting ducts)

• Nephron = functional unit of kidney

• Water, salts, urea pulled from blood when passing thru glomerulus into Bowman’s capsule

• Filtrate passes thru loop of Henle & distal tubule then collecting duct

• filtrate goes out ureter

• Most of nephron in cortex

IV. The kidney’s transport epithelia regulate the composition of

loodA. Production of Urine from Blood Filtrate

1. Filtration of Blood

* molecules filter out of blood & filtrate will have concentration similar to plasma

2. Secretion

* filtrate is joined by substances from interstitial fluid

* selective process

3. Reabsorption

* selective transport of filtrate substances back to interstitial fluid

* kidneys = central to homeostasis (clean wastes from blood & respond to fluid imbalances)

B. Transport Properties of the Nephron & Collecting Duct

1. proximal tubule: alters volume & composition of filtrate by reabsorption & secretion (salt)

2. descending loop of Henle: water

3. ascending loop of Henle: salt

4. distal tubule: K+ & NaCl conc. & pH

5. collecting duct: carries filtrate out (permeable to water --- conserves)

****** water-conserving ability of mammalian kidney = key

terrestrial adaptation

** controlled by nerves & hormones

V. Diverse adaptations of the vertebrate kidney have evolved in

different habitats

• Desert mammals: long loop of Henle to conserve water (urine is concentrated)

• Mammals in aquatic environment: short loops of Henle (urine is dilute)

VI. An animal’s nitrogenous wastes are correlated with its phylogeny &

habitat

• Metabolism of proteins & nucleic acids makes ammonia

A. Ammonia – excreted directly by aquaticB. Urea – requires much water & must be

eliminated quickly ; excreted by mammals & amphibians

C. Uric Acid – excreted by land snails, birds, reptiles; pastelike form thru cloaca (mixed w/ feces)

VII. Thermoregulation maintains body temperature within range

conducive to metabolism1. Conduction – direct transfer of heat

between environment & body surface (water more effective)

2. Convection - transfer of heat by movement of air or liquid past body surface

3. Radiation – emission of electromagnetic waves produced by object (warmed by sun)

4. Evaporation – loss of heat from liquids surface by turning to gas (not in moist environments)

VIII. Ectotherms vs. Endotherms

• Ectotherms – warms body by absorbing heat from surroundings

• Endotherms – derives body heat from metabolism

IX. Thermoregulation involves physiological & behavioral

adjustments1. Adjusting rate of heat exchange between

animal & surrounding: dilation & constriction

2. Cooling by evaporative loss: panting, sweating

3. Behavioral: sun, burrow, migrate

4. Changing rate of metabolic heat production: skeletal muscle activity

X. Comparative physiology reveals diverse mechanisms of

thermoregulationA. Invertebrates: behavior (huddle)B. Amphibians & Reptiles: mucus, burrowC. Fishes: swimD. Mammals & Birds: muscles, hormones,

dilation & constrict., fur & feathers, fat, blubber, saliva & urine

E. Humans: controlled by hypothalamus; cooling=dilation, sweat; warm= constriction & shivering