General Biology
“Maintenance of Life”
Controlling the Internal Environment
Excretion
Noppadon Kitana, Ph.D.
Department of Biology
Chulalongkorn University
September 12, 2012
Homeostasis
“Most animals can survive fluctuations in the
external environment that are more extreme than
any of their individual cells could tolerate.”
Homeostasis = steady-state
balance in the internal
environment of an animal’s
body
– Thermoregulation
– Osmoregulation
– Excretion
September
12, 2012
Regulating v.s. Conforming
• Mode of adaptation that animals use to cope with
environmental fluctuations
• Conformers = animals that
allow some conditions
within their bodies to vary
with external changes.
– Live in relatively stable
environment
– Energy requirement is
relatively low
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• Spider crabs (genus Libinia) live in environments
where salinity is relatively stable.
• Do not osmoregulate
• If placed in water of
varying salinity, they will
lose or gain water to
conform to the
environment.
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Regulating v.s. Conforming
• Mode of adaptation that animals use to cope with
environmental fluctuations
• Regulator = animals that
use mechanisms of
homeostasis to moderate
internal change.
– Live in fluctuate
environments
– Need energy for the
regulation
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Conformer v.s. Regulator
• No organisms are perfect regulators or conformers.
Salmon
– Use osmoregulation to maintain a
concentration of solutes in body fluids
– Conforming to external temperatures
• Regulation requires energy, and in some case, the
cost of regulation may outweigh the benefits of
homeostasis.
Lizard
– Conform in one situation and regulate in another
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Thermoregulation
• Each animal has an optimal temperature range.
• Within the range, animals maintain nearly constant
internal temperatures as the external temperature
fluctuates.
• The thermoregulation helps keep body temperature
within a range that enable
cells to function effectively.
– Metabolic rate
– Cellular respiration
– Enzyme activity
– Cell membrane integrity
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Physical Processes of Heat Exchange
An organism exchanges heat by four physical
processes.
1. Conduction
2. Convection
3. Radiation
4. Evaporation
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• Conduction is the direct transfer of heat between
molecules in direct contact with each other.
– For example, a lizard can increase body temperature
with heat conducted from a warm rock.
– Heat is conducted from higher to lower temperature.
– Rate and amount of heat transfer varies with different
materials.
• Convection is the transfer of heat by the
movement of air or liquid pass a surface.
– Occurs when a breeze contributes to heat loss from
the surface of animal with dry skin
– Also occurs when circulating blood moves heat from
an animal’s warm body core to the cooler extremities
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• Radiation is the emission of electromagnetic
waves by all objects warmer than absolute zero
(e.g. animal’s body, environment, and the sun)
– Radiation can transfer heat between objects that are
not in direct contact.
• Evaporation is the removal of heat from the
surface of a liquid that is losing some of its
molecules as gas.
– Evaporation of water from an animal has a strong
cooling effect.
– This can only occur if the surrounding air is not
saturated with water molecules.
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Physiological and Behavioral Adjustments
1. Adjusting heat exchange rate
- Use circulatory system
- Vasodilation (remove heat)
- Vasoconstriction (keep heat)
- Counter current heat exchange
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Counter current
heat exchange
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2. Cooling by evaporative heat loss
– Release water through skin & breath
– Evaporation = heat loss
– Accelerate by bathing,
panting & sweating
3. Behavioral response
– Move to cooler or hotter place
4. Change metabolic rate
– Metabolic heat production
– Birds and mammals can increase metabolic
heat production when exposed to cold.
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Endotherms v.s. Ectotherms
• Group animals according their source of body heat
• Ectotherm has such a low metabolic rate that the
amount of heat that it generates is too small to have
much effect on body temperature.
– Ectotherm body temperatures are almost entirely
determined by the temperature of the environment.
– e.g. invertebrates, fishes, amphibians, and reptiles
• Endotherm has high metabolic rate that generates
enough heat to keep its body temperature warmer
than the environment.
– e.g. mammals, birds, fishes, reptiles and insects
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Thermoregulations in Animals
Insect
• Usually an ectotherm
• Except
– Moth: increase heat using flight muscle
– Bee: increase heat using flight muscle & behavior
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Thermoregulations in Animals
Swimming muscle heat production
Fish
• Normally = ectotherm
• Some fishes can
regulate their own body
temperature.
Counter
current
heat exchange in shark
September 12,
2012
Thermoregulations in Animals
Amphibians and Reptiles
• Most, if not all, = ectotherm
• Low metabolic rate, small heat production
• Use behavioral adjustment e.g. basking or
relocating to a more suitable place
• Some could be temporary endotherm e.g. python
who can produce heat during egg incubation
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Thermoregulations in Animals
Birds and Mammals
• Most, if not all, = endotherm
• Maintain body temperature with
an aid of feather, hair, fat
• May increase body temperature
by:
– Shivering
– Non-shivering thermogenesis
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Feedback mechanism
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Feedback mechanism
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Fever (Pyrexia)
• Stimulate by certain pyrogen (such as
lipopolysaccharide from bacterial cell wall)
• Increase in set point of body temperature
• Fever = set point is above body temperature:
– Body sense a decreased in body temperature.
– shivering and vasoconstriction
• After fever = set point is below body temperature:
– Body sense an increase in body temperature.
– sweating and vasodilation
• Found in both endotherms and ectotherms
(behavioral fever)
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Fever
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Osmoregulation
• Animals must regulate the chemical composition of
its body fluids by balancing the uptake and loss of
water and fluids.
• Osmoregulation = management of the body’s
water content and solute composition,
• Based on controlling movements of solutes
between internal fluids and the external
environment.
– Regulates water movement by osmosis.
– Remove metabolic waste products before they
accumulate to harmful levels.
September 12, 2012
A
B
Salt: 15%
Salt: 80%
Water: 85%
Water: 20%
• Movement of water across a selectively permeable
membrane = osmosis
– Occurs whenever 2 solutions separated by a
membrane differ in osmotic pressure, or
osmolarity (moles of solute per liter of solution).
– The unit of measurement of osmolarity is
milliosmoles per liter (mosm/L).
• Hyperosmotic: more concentrated
• Hypoosmotic: less concentrated
• Isoosmotic: similar concentration
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Mode of Osmoregulation
• Osmoconformer are usually isoosmotic to the
surroundings and do not need special process to
control its osmolarity.
– Often live in water that has a stable composition and
have a very constant internal osmolarity
• Osmoregulator must control its internal osmolarity
because its body fluids are not isoosmotic with the
outside environment.
– Discharge excess water if it lives in a hypoosmotic
environment
– Take in water if it lives in a hyperosmotic environment
– Enables animals to live in environments that are
uninhabitable to osmoconformers, such as freshwater and
September 12, 2012
terrestrial habitats.
Osmoregulation in Marine Fish
• Live in hyperosmotic environment
• Constantly loose water through skin and gills
• Obtain water in food
and by drinking seawater
• Excrete ions by active
transport out of the gills
(chloride cells)
• Excrete salt ions in urine
• Produce very little urine
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Osmoregulation in Freshwater Fish
• Live in hypoosmotic environment
• Constantly gaining water by osmosis and losing
salts by diffusion.
• Excrete large amounts of
very dilute urine
• Regaining lost salts in food
• Obtain water while feeding
• Active uptake of salts from
their surroundings by gills
(chloride cells)
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Osmoregulation in Shark
I’m not sure if this is hypoosmotic
or hyperosmotic environment?
September 12, 2012
Osmoregulation in Shark
• Live in marine environment
• Salts diffuse into the body from seawater and
these salts are removed by the kidneys, a special
organ called the rectal gland, or in feces.
• Prevent water loss by accumulating 2 solutions in
the body:
– Urea = increase osmolarity
– Trimethylamine oxide (TMAO) = protects protein from
damage by urea
• As if living in hypoosmotic environment
• Water slowly enters the shark’s body by osmosis
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and in food, and is removed in urine.
Osmoregulation in Shark
September 12, 2012
Adaptations during Dehydration
• Some aquatic invertebrates living in temporary
ponds can lose almost all their body water and
survive in a dormant state (anhydrobiosis =
hidden life) when their habitats dry up.
• Tardigrades, or water bears, contain about 85% of
their weight in water when hydrated.
• Can dehydrate to less than 2% water and survive
in an inactive state for a decade until revived by
water.
September 12, 2012
• Anhydrobiotic animals must have adaptations
that keep their cell membranes intact.
• Mechanism that tardigrades use is still under
investigation
• Anhydrobiotic nematodes contain large amount of
sugars, especially the disaccharide trehalose.
– Trehalose seems to protect cells by replacing water
associated with membranes and proteins.
• Many insects that that survive in the winter also
utilize trehalose as a membrane protectant.
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Adaptations of Terrestrial Animal
• Adaptations that reduce water loss are key to
survival on land.
• Humans die if ~12% of their body water is loss.
• Most terrestrial animals have body coverings that
help prevent dehydration.
– Waxy layers in insect exoskeletons
– Shells of land snails
– Multiple layers of dead, keratinized skin cells.
• Being nocturnal (active at night) also reduces
evaporative water loss.
September 12, 2012
• Terrestrial animals lose water from moist
surfaces in their gas exchange organs, in urine
and feces, and across the skin.
• Balance the water budgets by drinking and eating
moist foods and by using metabolic water from
aerobic respiration.
• Some animals are well adapted for minimizing
water loss that they can survive in deserts without
drinking.
– For example, kangaroo rats lose so little water that
they can recover 90% of the loss from metabolic water
and gain the remaining 10% in their diet of seeds.
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Osmoregulation
in human v.s.
kangaroo rat
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Waste Disposal
• Depend on the ability of a layer or
layers of transport epithelium to move
specific solutes in controlled amounts
in particular directions.
• Epithelial cells are joined by
impermeable tight junctions.
• Selective permeable barrier
• In most animals, transport epithelia
are arranged into complex tubular
networks with extensive surface area.
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Salt-secreting glands
in Albatross
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Nitrogenous Waste
• Nitrogenous breakdown products of proteins and
nucleic acids are among the most important
wastes in terms of their effect on osmoregulation.
• Ammonia: small molecule, water soluble, but very
toxic
– common in aquatic species
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Nitrogenous Waste
• Nitrogenous breakdown products of proteins and
nucleic acids are among the most important
wastes in terms of their effect on osmoregulation.
• Urea: water soluble, ~105 times less toxic than
ammonia
– mammals, most adult amphibians, and many
marine fishes and turtles
September 12, 2012
Nitrogenous Waste
• Nitrogenous breakdown products of proteins and
nucleic acids are among the most important
wastes in terms of their effect on osmoregulation.
• Uric acid: insoluble in water, relatively nontoxic
– land snails, insects, birds, and many reptiles
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Nitrogenous
waste
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The kinds of
nitrogenous wastes
excreted depend
on an animal’s
evolutionary history
and habitat especially water
availability.
Excretory systems
• Dispose of metabolic
wastes and control body
fluid composition by
adjusting the rates of loss
of particular solutes
• Tubular excretory system
• Processes:
– Filtration
– Reabsorption
– Secretion
– Excretion
September 12, 2012
“Nephros
(Gr) = kidney”
Protonephridia:
Flame bulb systems
• Protonephridium (singular)
• Flatworms, rotifers, larval
mollusks, annelids &
lancelets
• Function in
osmoregulation or
excretion
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• A branching network of
dead-end tubules capped
by a “flame bulb”
• Cilia draws water and
solutes from interstitial
fluid.
• Urine in the tubules exits
through openings called
nephridiopores.
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Metanephridia
• Metanephridium
(singular)
• 1 pair / segment
• Most annelids
(earthworm)
• Function in
osmoregulation and
excretion
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• Collect body fluids from
the coelom through a
nephrostome and
release the fluid
through the
nephridiopore
• Transport epithelium reabsorbs most solutes and
returns them to the blood in the capillaries.
• Wastes are kept in the tubule (bladder) and dumped
outside.
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Malpighian tubules
• Insects and other
terrestrial arthropods
• Function in excretion
and osmoregulation
• Dead-end at tips that
are immersed in
hemolymph and open
into the digestive
system.
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• Transport epithelium
secretes certain
solutes including
nitrogenous wastes
from hemolymph into
the tubule.
• Water and most solutes
are reabsorbed at
rectum.
• Nitrogenous waste
(uric acid) is eliminated
along with the feces.
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Kidney
• Mammalian kidney has two distinct regions, an
outer renal cortex and an inner renal medulla.
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• In human, cortical nephrons (80%) have reduced
loops of Henle and are almost entirely confined to
the renal cortex.
• Juxtamedullary nephrons (20%) have welldeveloped loops that extend deeply into the renal
medulla.
September 12, 2012
Nephron
• Blood vessels
–
–
–
–
–
Afferent arteriole
Efferent arteriole
Glomerulus
Peritubular capillaries
Vasa recta
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• Ducts / Tubules
–
–
–
–
–
Bowman’s capsule
Proximal tubule
Loop of Henle
Distal tubule
Collecting duct