chapter 44 controlling the internal environment. i. cells require a balance between water uptake...
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CHAPTER 44
CONTROLLING THE INTERNAL ENVIRONMENT
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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
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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)
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• Large changes = usually fatal (stenohaline)
euryhaline can survive
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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
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• Terrestrial animals:
protective outer layers (shells, skin)
drinking & eating moist food
behavior (nocturnal)
excretory organs
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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
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C. Malpighian Tubules in Insects
- remove nitrogenous wastes from hemolymph
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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)
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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
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• Filtrate passes thru loop of Henle & distal tubule then collecting duct
• filtrate goes out ureter
• Most of nephron in cortex
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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
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3. Reabsorption
* selective transport of filtrate substances back to interstitial fluid
* kidneys = central to homeostasis (clean wastes from blood & respond to fluid imbalances)
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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)
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****** water-conserving ability of mammalian kidney = key
terrestrial adaptation
** controlled by nerves & hormones
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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)
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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)
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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)
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4. Evaporation – loss of heat from liquids surface by turning to gas (not in moist environments)
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VIII. Ectotherms vs. Endotherms
• Ectotherms – warms body by absorbing heat from surroundings
• Endotherms – derives body heat from metabolism
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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
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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