Regulating the Internal Environment

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Chapter 44
Regulating the Internal Environment
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Homeostasis

• Thermoregulation
• Osmoregulation
• Excretion

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Homeostasis

• All organisms must maintain a constant internal
  environment to function properly
• Temperature
• pH
• ion levels
• hormones

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Negative Feedback
Body Temperature Regulation
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Coping with Environmental Fluctuations Regulati
ng Endotherms are thermoregulators Fundulus-osmor
egulator Conforming Ectotherms Many inverts-
nonregulator
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Regulators Conformers
Spider crab Libinia
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Anadromous Salmon
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Four physical processes account for heat gain or
loss

• Heat exchange by
• Conduction- transfer of heat between objects in
  direct contact with each other
• Convection- heat is conducted away from an object
  of high temp to low temp
• - Rate varies with different materials
• Radiation- transfers heat between objects not in
  direct contact
• - sun energy
• Evaporation- change of liquid to vapor
• - cooling

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Heat exchange between an organism and its
environment
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Ectotherm vs Endotherm
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• Advantages of Endothermy
• Maintains stable body temp
• Cooling heating the body
• cooling and heating the body
• high levels of aerobic metabolism
• sustains vigorous activity for much longer than
  ectotherms
• Long distance running
• Flight

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Disadvantages of Endothermy

• Greater food consumption to meet metabolic needs
• Human metabolic mate at 200C at rest
• 1,300 to 1,800 kcal per day.
• American alligator metabolic rate at 200C at
  rest
• 60 kcal per day at 200C.

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Mechanisms for thermoregulation

• Insulation
• Fur
• Hair
• Feathers
• Fat
• Blubber
• Evaporative cooling
• sweating, panting, bathing
• Shivering
• Nonshivering thermogenesis brown fat
• Circulation adaptations
• Countercurrent exchange
• Vasodilatation (cooling)
• Vasoconstriction (heat conservation)
• Behavioral responses

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Countercurrent heat exchangers
Goose leg
Dolphin flipper
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Evaporative Cooling
Hippos bathing
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Brown Fat Non-shivering Thermogenesis

• Brown fat- generates heat
• important in neonates, small mammals in cold
  environments, and animals that hibernate
• Located in neck and in inner scapula area
• Non-shivering Thermogenesis
• Larges amts of heat produced by oxidizing fatty
  acids in the mitochondria

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Regulating Body Temp in Humans
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• Acclimatization to New Env. Temps.
• Endotherms (birds and mammals) grow a thicker
  fur coat in the winter and shedding it in the
  summer - and sometimes by varying the capacity
  for metabolic heat production seasonally.
• Ectotherms compensate for changes in body
  temperature through adjustments in physiology and
  temperature tolerance.
• For example, winter-acclimated catfish can only
  survive temperatures at high as 28oC, but
  summer-acclimated fish can survive temperatures
  to 36oC.

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• Some ectotherms that experience subzero body
  temperatures protect themselves by producing
  antifreeze compounds (cryoprotectants) that
  prevent ice formation in the cells.
• In cold climates, cryoprotectants in the body
  fluids let overwintering ectotherms, such as some
  frogs and many arthropods and their eggs,
  withstand body temperatures considerably below
  zero.
• Cyroprotectants are also found in some Arctic and
  Antarctic fishes, where temperatures can drop
  below the freezing point of unprotected body
  fluids (about -0.7oC).

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• Cells can often make rapid adjustments to
  temperature changes.
• For example, marked increases in temperature or
  other sources of stress induce cells grown in
  culture to produce stress-induced proteins,
  including heat-shock proteins, within minutes.
• These molecules help maintain the integrity of
  other proteins that would be denatured by severe
  heat.
• These proteins are also produced in bacteria,
  yeast, and plants cells, as well as other
  animals.
• These help prevent cell death when an organism is
  challenged by severe changes in the cellular
  environment.

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Hibernation long-term torpor as an adaptation to
long-term winter cold and food shortage

• Torpor in Ground Squirrels
• Body temperature 37oC
• Metabolic rate 85 kcal per day.
• During the eight months the squirrel is in
  hibernation, its body temperature is only a few
  degrees above burrow temperature and its
  metabolic rate is very low.

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Body Temperature and metabolism during
hibernation of Beldings ground squirrel
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Osmoregulation
Osmoregulation- the control of the concentration
of body fluids. Diffusion- movement of substance
from an area of greater concentration to an area
of lower concentration Osmosis- diffusion of
water through a semipermeable membrane
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• Adaptation to Marine Environment
• Reducing salt
• Seabird and marine iguana- nasal salt secreting
  gland
• Sea snake- sublingual gland
• Crocodile- lacrimal gland
• Fish gills- chloride cells
• Shark- rectal gland

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Salt Excretion in Birds
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Nitrogenous Waste Excretion

• Ammonia- toxic
• Excrete directly into water- jellies
• Detoxify?urea
• Urea- need lots of water to get rid of
• Uric Acid- birds reptiles
• more costly to produce than urea, but needs less
  water to be removed

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Strategies to remove Nitrogenous Waste
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Balancing NaCl in Blood

• Osmoconformer isoosmotic
• Osmoregulator hyper-, hypo-, ureoosmotic
• Euryhaline wide tolerance range
• Stenohaline narrow tolerance range

Osmols- total solute concentration in moles of
solute/liter of solution
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Marine Fish hypoosmotic
Less salt than external environment
H2O continually leaves body
continually drinks seawater
excretes salt through gills
produces small amts of dilute urine
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Freshwater Fish hyperosmotic
H2O continually enters body
does not drinks water
More salt than external environment
produces large amts of dilute urine
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Shark and Coelacanth ureoosmotic
Maintains high levels of urea and TMAO in blood
excretes salt through rectal gland
coelacanth
Rana cancrivora
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Hagfish ionosmotic
nonregulator
Seawater concentration internal concentration
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Osmolarity in Freshwater and Saltwater
Osmolarity- measure of total solutes(dissolved
particles) Ions FW m osmol/l SW m
osmol/l Na 1 470 Cl- 1 550 Ca
variable 10 Total 10 1000
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Concentration of Ions
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• Adaptations to Dry Environment
• Many desert animals dont drink water
• 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.
• Also have long loop of Henle

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• Most excretory systems produce a filtrate by
  pressure-filtering body fluids into tubules.

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Diverse excretory systems are variations on a
tubular theme

• Flatworms have an excretory system called
  protonephridia, consisting of a branching
  network of dead-end tubules.
• The flame bulb draws water and solutes from the
  interstitial fluid, through the flame bulb, and
  into the tubule system.

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• Metanephridia consist of internal openings that
  collect body fluids from the coelom through a
  ciliated funnel, the nephrostome, and release the
  fluid through the nephridiopore.
• Found in most annelids, each segment of a worm
  has a pair of metanephridia.

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• Insects and other terrestrial arthropods have
  organs called Malpighian tubules that remove
  nitrogenous wastes and also function in
  osmoregulation.
• These open into the digestive system and
  dead-end at tips that are immersed in the
  hemolymph.

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Nephron
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Hormonal Control via Negative Feedback
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Hormonal Control