Thermoregulation

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Thermoregulation

• Concept 40.3-Homeostatic Process for
  Thermoregulation involve Form, Function, and
  Behavior
• Susan Chen
• AP Biology 1st Pd.

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Overview

• Thermoregulation- the process by which animals
  maintain an internal temp. within a tolerable
  range
• Physiological processes are very sensitive to
  changes in body temp.
• Ex. Changes in enzyme-mediated reactions, and the
  membrane becomes more rigid or fluid as temp.
  rise or fall

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Endothermy

• Endothermic describes animals warmed mostly by
  heat generated form metabolism.

• Ex. Birds and Mammals

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Ectothermy

• Ectothermic describes animals that gain most of
  their heat form external sources.

• Ex. Amphibians, lizards, snakes, turtles, many
  fishes, and most invertebrates

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Endotherms vs. Ectotherms

• Endothermy and ectothermy are NOT mutually
  exclusive modes of thermoregulation.
• Ex. A bird is mainly endothermic, but it may also
  warm itself in the sun on a cold morning, much as
  an ectothermic lizard does.
• Because their heat source is mainly
  environmental, ectotherms generally need to
  consume much LESS food than endotherms of
  equivalent size.

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Variations in Body Temp.

• Poikilotherms- animals whose body temp. varies
  with its environment.
• Homeotherms- animals with a relatively constant
  body temp.
• There is NO FIXED relationship btw source of heat
  with stability of temp.

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Variations in Body Temp. Continue

• Common Misconceptions Ectotherms are
  "cold-blooded" and endotherms are "warm blooded"
• Ectotherms do NOT necessarily have low body temp.
• Ex. Many ectothermic lizards have higher body
  temp. than mammals when sitting in the sun.
• "Cold-blooded" and "warm-blooded" are MISLEADING
  and have been dropped from the scientific vocab.

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Balancing Heat Loss and Gain

• Thermoregualation depends on an animal's ability
  to control the exchange of heat with its
  environment.
• An animal, like any other animal exchange heat by
  4 physical processes CONDUCTION, RADIATION,
  CONVECTION, EVAPORATION.

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Balancing Heat Loss and Gain Insulation

• Mammals and birds can reduce the flow of heat btw
  them and its environment with insulation.
• Sources of insulation hair, feathers and fat

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Balancing Heat Loss and Gain Circulatory
Adaptations

• Circulatory systems provide the major routes for
  heat flow btw. the interior and exterior of the
  body.
• Vasodilation- an increase in the diameter of
  superficial blood (hence heat) caused by
  relaxation of muscles of the vessel walls
• Vasoconstriction- reduces blood flow and heat
  transfer by decreasing the diameter of
  superficial vessels
• Birds and mammals reduce heat loss by
  countercurrent exchange.

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Balancing Heat Loss and Gain Circulatory
Adaptations Cont.
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Balancing Heat Loss and Gain Evaporative Cooling
and Behavioral Responses

• Panting, sweating, and bathing increase
  evaporation, which in turn, cools the body.
• BOTH ectotherms and endotherms adjust the rate
  of heat exchange with their environment by
  behavioral responses.
• -Ex.
• 1) Hibernation
• 2) Moving from the sun to the shade
• 3) Restricting activities to the night

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Balancing Heat Loss and Gain Metabolic Heat
Production

• Heat production (THERMOGENSIS) is increased by
  muscle activity----------shivering and moving.
• NONSHIVERING THERMONGENSIS occurs when certain
  hormones cause the mitochondria to increase
  metabolic activity and produce heat instead of
  ATP.
• BROWN FAT in the neck and btw the shoulders is
  specialized for rapid heat production.

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Balancing Heat Loss and Gain Metabolic Heat
Production Cont.

• SOME ectoderms can also generate heat through
  spasmodic muscle contraction suggesting that
  certain groups of dinosaurs could have been
  endothermic.

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Acclimatizations in Thermoregulation

• Acclimatizations- temporary changes in response
  to external environment
• NOT to be confused with ADAPTATIONS, a process of
  change n a population brought about by natural
  selection acting over many generations.
• In birds and animals, acclimatizations to
  seasonal temperature changes often includes
  adjusting the amount of insulation.
• Ex. Growing a thicker coat of fur in winter and
  shedding it in the summer

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Acclimatizations in Thermoregulation Cont.

• Acclimatizations in ectotherms often involve
  adjustments at cellular levels
• Ex.
• -Cell produce variant of enzymes w/same
  function but DIFFERENT optimal temp.
• -Proportions of saturated and unsaturated
  lipids in membrane change unsaturated lipids
  help keep membrane more fluid at lower temp.

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Physiological Mechanisms

• Regulation of body temp. in humans is brought
  about by a complex system based on feedback
  mechanism.
• Hypothalamus- brain region, where the sensors for
  thermoregulation are concentrated.
• A group of nerve cells functions as a thermostat.

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Osmoregulation

• Concept 44.1-Osmoregulation balances the uptake
  of water and solutes.

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Overview

• Osmoregulation- the process by which animals
  control solute concentration and balance water
  gain and loss.
• Animals' surroundings presents severe
  osmoregulatory challenges.
• Ex.
• -Desert animals live an environment that can
  quickly deplete their body water
• -Marine animals also face potential problem of
  dehydration
• -Freshwater animals live in an environment that
  threatens to flood and dilute their body fluids

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Osmosis

• ALL animals face the need for osmoregulation
• Osmosis is the movement of water across a
  selectively permeable membrane
• It occurs when 2 solutions seperated by a
  membrane differ in osmotic pressure, or
  OSMOLARITY (total solute concentration, expressed
  as molarity)

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Osmotic Challenges

• All animals maintain water balance in 2 ways.
• They are either
• Osmoconformers- isoosmotic with its surroundings
• Osmoregulators- controls with its internal
  osmolarity independent of that of its environment
• All osmoconformers are MARINE animals

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Osmotic Challenges Continue

• Stenohaline describes MOST animals, whether
  osmoconformers of osmoregulators, that cannot
  tolerate substantial changes in external
  osmolarity.
• Euryhaline describes CERTAIN osmoconformers and
  osmoregulators that can survive large
  fluctuations in external osmolarity.

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Osmotic Challenges in Marine Animals

• Most marine animals are osmoconformers------their
  osmolarity is the SAME as that of seawater.
• But they differ considerably in concentration of
  specific solutes.
• Marine bony fishes constantly lose water by
  osmosis.

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Osmotic Challenges in Marine Animals Cont.

• They must balance water loss by drinking large
  amounts of water----they then use their gills and
  kidneys to rid themselves of salt.
• In gills, specialized CHLORIDE cells transport
  chloride ions (Cl-) out and sodium ions (Na)
  follow passively.
• Kidneys excreted excess calcium, magnesium,
  sulfate w/small loss of water.

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Osmotic Challenges in Freshwater Animals

• Their problem is the opposite of marine animals.
• They have an osmolarity higher than that of their
  environment, so they gain water by osmosis and
  lose salt by diffusion.
• Some fishes such as Salmon, can do both.

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Osmotic Challenges in Freshwater Animals Cont.

• Water balance is solved by almost drinking NO
  water and excreting large amounts of very dilute
  urine.
• Salt is replenished by eating at the same time.
• Chloride cells in gills actively transport Cl-
  into the body and Na follows.

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Osmotic Challenges in Land Animals

• Water is lost through urine and feces, across
  skin, and from moist surface in gas exchange.
• Body coverings of most terrestrial animals help
  prevent dehydration.
• Ex. waxy layers of insect exoskeleton, shells of
  land snails, and the layers of dead, keratinized
  skin

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Osmotic Challenges in Land Animals Cont.

• Many terrestial animals esp. desert animals are
  nocturnal, which reduces evaporative water loss.
• They can also maintain water balance by eating
  and drinking moist foods and by producing water
  metabolically through CELLULAR RESPIRATION.

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Energetics of Osmoregulation

• There is an ENERY COST for maintaining osmolarity
  btw its body and the external environment.
• Osmoregulation uses ACTIVE TRANSPORT to maintain
  solute concentration.
• The energy cost for osmoregulation depends on 3
  factors
• How different an animal's osmolarity is form its
  surroundings
• How easily water and solutes can move across the
  animal's surface
• How much work is required to pump solutes across
  the membrane

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Transport Epithelia in Osmoregulation

• Water balance and waste disposal depends on
  transport epithelia
• Tranpsort Epithelia- layers of specialized
  epithelial cells that regulate the solute
  movements for waster disposal and for tempering
  changes in body fluids.

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NOTE The Princeton Review for AP Biology does
NOT go over Thermoregulation and Osmoregulation.
Hope you paid attention. Have fun rereading the
chapters 40 and 44 if you did not.
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Review Questions

1. Compare the mechanism of thermoregulaton with
   osmoregulation.
2. What modes of heat exchange is involved in wind
   chill, when moving air feels colder than still
   air at the same temp.?
3. Flowers differ in how much sunlight they absort.
   Why might this matter to a humming bird seeking
   nectar on a cold morning?
4. The movement of salt from the surrounding water
   to the blood of a freshwater fish requires the
   expenditure of energy in the form of ATP. Why?
5. Why aren't any freshwater animals osmoconformers?