TEMPERATURE
REGULATION AND WATER
BALANCE
Ectotherm Vs. Endotherm
Ectotherms –have a body temperature that is more or less determined
by the temperature of the surrounding environment
Endotherms – have a relatively constant body temperature that is
usually higher than the surrounding environment
temperature
Ectotherms:
‘Ecto’ – mean outside
‘Therm’ – means heat
Generally if the climate is hot ectotherms including their blood is hot. If
the climate is cold so to is the animal including the blood. This information
dispels the idea that reptiles are cold blooded.
Some ectotherms alter their behaviours to maintain body temperature.
For example reptiles are inactive in cold weather and in the warmer
weather can often be seen out in the sunshine warming up. The warming
up of the body temperature results in an increase in activity level.
Some ectotherms also produce heat through extensive movement such
as flying and swimming.
Ectotherms include:
• Snakes
• Lizards
• Fish
• Frogs
Endotherms:
‘Endo’ – means inside
‘Therm’ – means heat
Endotherms produce a large amount od heat internally. They also have
insulating structures such as feathers, fur and fat layers to reduce and slow
the loss of heat to the environment.
Keeping warm however costs energy for these animals. The cost is also
high in smaller animals who have a large surface area to lose heat and
less tissue to produce heat. Due to this small animals require more food
than larger animals to keep up with energy demands.
In endotherms more than 6 degrees above core temperature is lethal.
Temperatures can drop significantly if the animal can survive the reduced
blood flow and reduced cellular metabolism (such as hibernation).
Endotherms include:
• Birds
• Mammals
• Humans
Temperature Regulating Pathways:
The regulation of temperature in humans is an example of the way
different sensory detectors work together to produce an integrated
response.
Arterial blood has the most constant temperature. The relatively constant
temperature of other body parts is an indicator of a good arterial blood
supply
In endotherms a group of temperature-sensitive cells in the hypothalamus
act as misalignment detectors, triggering homeostatic responses if blood
temperature deviated from optimum range.
Temperature receptors are also found in the skin. A decrease in
temperature will initiate responses such as a decrease in blood flow to the
skin to reduce the amount of heat lost to the environment.
Skin detectors are an example of a disturbance detector, detecting and
responding to environmental temperature change before there is a
change in the core body temperature.
Regulating Heat Exchange:
Factors which are involved in regulating the rate of heat exchange
between an animal and its environment include:
•
•
•
•
The effective temperature difference between the two
The area of exposed surface
The efficiency of any insulation against heat exchange
Physiological process involving evaporation and circulatory changes
Heat Loss:
When environmental temperature is lower than body temperature
animals tend to lose heat by radiation, evaporation, conduction and
direct loss through body fluids
If temperature of the environment is higher than body temperature the
only way that animal will lose heat is through evaporation (sweating,
panting and the licking of fur)
Heat gain:
Heat is generated by metabolism in cells. Endothermic animals have
insulation and physiological mechanisms that allow them to reattain this
heat in order to maintain a constant body temperature
Insulation:
Endotherms have fur and feathers for insulation which reduce heat
exchange with the environment. Fur and feathers trap a layer of warm air
next to the body which reduces to gradient between the temperature of
the climate and the body. This decrease in temperature gradient reduces
heat loss
Countercurrent Heat Exchange:
Countercurrent heat exchange works by way of warm blood in the
arteries moving parallel and very close to the cooler venous return. The
proximity of two fluids of different temperatures creates the necessary
conditions for the exchange of heat. Heat is transferred from the warmer
arterial flow into the cooler venous flow which then returns the warm
blood to the body's core. The now somewhat cooler arterial flow
proceeds to the relatively poorly insulated appendages. The net result is
that the core remains warm and the appendages perpetually cool.
Countercurrent heat-exchangers acting to conserve core heat are
commonly found in the extremities of animals living in cold habitats,
particularly in the legs or flippers of polar and cool temperate birds and
mammals.
http://www.biology.ualberta.ca/facilities/multimedia/uploads/zoology/counter%20curre
nt.html
Behavioural regulation:
Behaviours that regulate heat exchange:
• Curling up to sleep in the cold (reduces surface areas for heat loss)
• Huddling together (to reduce surface area for heat loss)
• Moving out of the sun (to reduce heat gain)
• Moving underground (to reduce heat gain)
• Restricting activity to night-time (to reduce heat loss or gain)
• Altering the amount of clothing being worn (to increase surface area
for heat loss or to decrease it)
• Altering body temperature (to either increase of decrease heat gain)
Controlling heat production:
It is more energy efficient to reduce heat loss and increase heat gain that
to use up food and oxygen to increase metabolic heat production
Metabolic heat can be increased by shivering or increasing cellular
activity in brown fat.
Water Balance and Salt Levels:
Maintaining water balance is necessary to control salt concentrations.
Salts form ions in solution and cells require the concentration of ions to be
held within narrow limits for biochemical processes to occur efficiently
Some ions are important for regulating pH which is critical for enzyme
functioning.
Water balance is a result of water intake and water loss. In organisms net
movement of water occurs as a result of osmosis which is governed by
solute concentration.
Water Balance in Aquatic Animals:
Invertebrates:
Invertebrates have body fluids with an osmotic concentration equal to
that of sea water. They therefore do not need to expend energy to
maintain osmotic balance.
Bony fish:
Freshwater fish
Marine fish
Have a body fluid which is more
concentrated that the water they
live in
Have a body fluid which is less
concentrated than the water they
live in
Maintain their salt and water
balance by:
• Rarely drinking water
• Excreting large amounts of very
dilute urine
• Actively absorbing salt via
specialised cells in their gills
Maintain their salt and water
balance by:
• Drinking almost continuously
• Producing small amounts of urine
• Actively excreting salt from
specialised cells in their gills
Cartilaginous fish:
Marine fishes such as sharks and rays retain an extraordinarily high amount
of urea in their blood. This retention increases their osmotic gradient to
equal that of sea water. This means that no energy needs to be spent to
maintain osmotic balance
Amphibians:
The majority of amphibians are freshwater, particularly in the Laval stage
and during breeding. Freshwater amphibians lose salt and gain water via
osmosis through their skin.
Terrestrial Organisms – Coping with Limited Water
Water gain in animals can be achieved through:
• Actively seeking out water however, this may lead to further water loss
in some environments, this will require energy
• Food intake (all food contains some water), this will require energy
• Cellular respiration also create metabolic water , this will require
energy
Water loss in animals:
• Respiratory surfaces must be moist so air breathers always lose water
from evaporation (less water is lost from humid air)
• Cool air carries less water than warm air
• Water is also lost form the kidneys when expelling nitrogenous wastes,
as well as from the gut when expelling faeces
• The kidney in mammals allows for water balance by creating
concentrated urine
Glossary:
Ectotherm
Endotherm
Hibernate
Core body temperature
Misalignment detector
Disturbance detector
Heat exchange
Insulation
Countercurrent flow
Metabolic heat
Brown fat
Water balance
Osmosis
kidneys
Complete the following:
Key Questions:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
Chapter Review Questions:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11