Chapter 44 - CR97-03-1 - Chapter 44 Osmoregulation and...

Chapter 44
Chapter 44
Osmoregulation and Excretion
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Overview: A balancing act
Overview: A balancing act
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The physiological systems of animals operate
in a fluid environment
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The relative concentrations of water and solutes in
this environment must be maintained within fairly
narrow limits
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Freshwater animals show adaptations that reduce water
uptake and conserve solutes
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Desert and marine animals face desiccating environments
with the potential to quickly deplete the body water
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Osmoregulation regulates solute
concentrations and balances the gain and loss
of water
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Excretion gets rid of metabolic wastes
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44.1: Osmoregulation balances the uptake
and loss of water and solutes
and loss of water and solutes
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Osmoregulation is based largely on controlled
movement of solutes between internal fluids and
the external environment
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Cells require a balance between osmotic gain and loss
of water
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Water uptake and loss are balanced by various
mechanisms of osmoregulation in different
environments
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Osmoconformers are marine animals that are
isoosmotic with their surroundings and do not regulate
their osmolarity
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Osmoregulators expend energy to control water uptake
and loss while living in either hyperosmotic or
hypoosmotic environments
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Most animals are said to be stenohaline
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They cannot tolerate substantial changes in
external osmolarity
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Euryhaline animals can survive large
fluctuations in external osmolarity
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Marine invertebrates are osmoconformers
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Most marine vertebrates and some invertebrates
are osmoregulators
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Marine bony fishes are hypoosmotic to sea water and
lose water by osmosis and gain salt by both diffusion and
from food they eat
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These fishes balance water loss by drinking seawater
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Freshwater animals constantly take in water from
their hypoosmotic environment
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They lose salts by diffusion
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Freshwater animals maintain water balance by
excreting large amounts of dilute urine
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Salts lost by diffusion are replaced by foods and uptake
across the gills
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Some aquatic invertebrates living in temporary ponds
can lose almost all their body water and survive in a
dormant state
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This adaptation is called anhydrobiosis
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Land animals manage their water budgets by drinking
and eating moist foods and by using metabolic water
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Transport epithelia are specialized cells that regulate
solute movement
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Essential components of osmotic regulation and metabolic
waste disposal
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Arranged into complex tubular networks
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Example: The salt glands of marine birds, which remove
excess sodium chloride from the blood (Fig 44.7) 5
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44.2: An animal’s nitrogenous wastes reflect
its phylogeny and habitat
its phylogeny and habitat
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The type and quantity of an animal’s waste products
may have a large impact on its water balance
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Among the most important wastes
are the nitrogenous breakdown
products of proteins and nucleic
acids
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