Transcript URIC ACID - cloudfront.net

CHAPTER 44
Osmoregulation and
Excretion
OVERVIEW: A BALANCING ACT
Physiological systems of animals operate in a fluid
environment
 Relative concentrations of water and solutes must be
maintained within fairly narrow limits

Freshwater animals show adaptations that reduce water
uptake and conserve solutes
 Desert and marine animals face desiccating (dehydrating)
environments that can quickly deplete body water

Osmoregulation regulates solute concentrations and
balances the gain and loss of water
 Excretion gets rid of metabolic wastes

CONCEPT 44.2: AN ANIMAL’S NITROGENOUS
WASTES
REFLECT ITS PHYLOGENY AND HABITAT
The type and quantity of an animal’s waste products may
greatly affect its water balance
 Among the most important wastes are nitrogenous
breakdown products of proteins and nucleic acids

Nucleic acids
Proteins
Amino acids
Nitrogenous bases
—NH2
Amino groups
(nitrogenous waste)
HOW these waste
products are excreted
depends on how
much water an
organism needs to
maintain homeostasis
This is dependent on
their habitat!
Most aquatic
animals, including
most bony fishes
More H2O
needed to
excrete
Ammonia
Mammals, most
amphibians, sharks,
some bony fishes
Urea
Many reptiles
(including birds),
insects, land
snails
Uric acid
More energy
needed to
excrete
FORMS OF NITROGENOUS WASTES: AMMONIA

Animals that excrete nitrogenous wastes as ammonia need
lots of water


So… they live in an environment where water is abundant.
They release ammonia across the whole body surface or
through gills
Freshwater animals
Marine invertebrates
FORMS OF NITROGENOUS WASTES: UREA
Animals that produce urea have a limited source of water
 The liver of mammals and most adult amphibians converts
ammonia to less toxic urea
 The circulatory system carries urea to the kidneys, where it is
excreted

If liver can’t get rid of
waste, there is a
buildup of uric acid in
the blood.
 It can crystallize in the
joints and cause
inflammation of the
joints.
 Condition is known as
gout

FORMS OF NITROGENOUS WASTES: URIC ACID
Animals that excrete uric acid have a critical problem with
getting water some time in their lifetime
 Insects, land snails, and many reptiles, including birds, mainly
excrete uric acid


Lay eggs with limited supply of water inside the egg.

Note: eggshells are impermeable to water so it won’t lose any water, but...
NH3
NH3
Uric acid
Uric acid
NH3
Uric acid
H2O
NH3
H2O
Uric acid
Contamination
No Contamination
FORMS OF NITROGENOUS WASTES: URIC ACID

Uric acid is largely insoluble in water and can be secreted as
a paste with little water loss
THE INFLUENCE OF EVOLUTION
NITROGENOUS WASTES
AND
ENVIRONMENT
ON
The kinds of nitrogenous wastes excreted depend on an
animal’s evolutionary history and habitat
 The amount of nitrogenous waste is coupled to the animal’s
energy budget

THE INFLUENCE OF EVOLUTION AND
ENVIRONMENT ON NITROGENOUS WASTES

Remember, there are 3 general wastes products
ammonia
urea
uric acid
Increasing amount of water

Special cases:
Lungfish: make ammonia when there’s a lot of water,
urea when pond dries out
 Aquatic mollusks make ammonia, terrestrial snails make
urea

CONCEPT 44.1: OSMOREGULATION BALANCES
THE UPTAKE
AND LOSS OF WATER AND SOLUTES
Osmoregulation is based largely on controlled movement of
solutes between internal fluids and the external environment
 Cells require a balance between osmotic gain and loss of
water
 Various mechanisms of osmoregulation in different
environments balance water uptake and loss
 Terms to remember:

Osmotic pressure: solute “pull”
 Osmotic potential: water concentration
 Hyper- , hypo-, iso- tonic solutions

OSMOTIC CHALLENGES
Osmoconformers, consisting only of some marine animals,
are isoosmotic (isotonic) with their surroundings and do not
regulate their osmolarity
 Osmoregulators expend energy to control water uptake and
loss in a hyperosmotic (hypertonic) or hypoosmotic
(hypotonic) environment

Most animals are stenohaline; they cannot tolerate
substantial changes in external osmolarity
 Euryhaline animals can survive large fluctuations in external
osmolarity

MARINE ANIMALS
Most marine invertebrates are osmoconformers
 Most marine vertebrates and some invertebrates are
osmoregulators


Marine bony fishes are hypoosmotic to sea water
They are in a hypertonic environment
 Constantly lose water (as if they were in a desert)

They lose water by osmosis and gain salt by diffusion and
from food
 They balance water loss by drinking seawater

Gain of water and
salt ions from food
and by drinking
seawater
Osmotic water loss
through gills and other parts
of body surface
[hypotonic]
Excretion of
salt ions
from gills
Osmoregulation in a saltwater fish
Excretion of salt ions
and small amounts
of water in scanty
urine from kidneys
[hypertonic]
TRANSPORT EPITHELIA
Transport epithelia are specialized cells that regulate solute
movement
 They are essential components of osmotic regulation and
metabolic waste disposal
 They are arranged in complex tubular networks
 An example is in salt glands of marine birds, which remove
excess sodium chloride from the blood

Nasal salt gland
(acts as a filter)
Nostril
with salt
secretions
FRESHWATER ANIMALS

Freshwater animals constantly take in water from their
hypoosmotic environment

Need: get rid of extra water, keep salts
They lose salts by diffusion and maintain water balance by
excreting large amounts of dilute urine
 Salts lost by diffusion are replaced by foods and uptake
Osmotic water gain
across the gills
through gills and other parts

of body surface
Uptake of
water and some
ions in food
[hypotonic]
[hypertonic]
Uptake of
salt ions
by gills
Osmoregulation in a freshwater fish
Excretion of
large amounts of
water in dilute
urine from kidneys
ANIMALS THAT LIVE IN TEMPORARY WATERS
Some aquatic invertebrates in temporary ponds lose almost
all their body water and survive in a dormant state
 This adaptation is called anhydrobiosis (“life without water”)

100 µm
100 µm
Hydrated tardigrade
Dehydrated
tardigrade
LAND ANIMALS

Land animals
manage water
budgets by
drinking and
eating moist
foods and using
metabolic water
Water
balance in a
kangaroo rat
(2 mL/day)
Ingested
in food (0.2 mL)
Water
balance in
a human
(2,500 mL/day)
Ingested
Ingested
in food
in liquid
(750 mL)
(1,500 mL)
Water
gain
Derived from
metabolism (1.8 mL)
Water
loss
Feces (0.09 mL)
Urine
(0.45 mL)
Evaporation (1.46 mL)
Derived from
metabolism (250 mL)
Feces (100 mL)
Urine
(1,500 mL)
Evaporation (900 mL)
Desert animals get major water savings from simple
anatomical features
Water lost per day
(L/100 kg body mass)

4
3
2
1
0
Control group
(Unclipped fur)
Experimental group
(Clipped fur)