OSMOREGULATION

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OSMOREGULATION EXCRETION

• Chapter 44

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OVERVIEW

• Osmoregulation
• Relative concentrations of water and solutes must
  be maintained in a variety of environments (land,
  freshwater, marine)
• Excretion
• Metabolism creates waste that must be expelled
  from the body
• Proteins and nucleic acids present a problem
  because ammonia (primary waste product) is toxic

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44.1 OSMOREGULATION

• Balancing the uptake and loss of water and
  solutes over time. If they dont osmosis will
  cause animal cells to swell and burst or shrivel
  and die.
• Isoosomotic two solutions with the same
  osmolarity
• Hyperosmotic solution with the greater
  concentration of solutes
• Hyposomotic solution with the more dilute
  concentration of solutes
• Water flows from a hyposomotic solution to a
  hyperosmotic one.

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TWO BASIC SOLUTIONS

• 1 (only available to marine animals) is to be
  isoosomotic with the environment.
• Osmoconformer
• Does not adjust its internal osmolarity
• Live in water that is fairly stable
• 2 (available to any animal) is to control its
  internal osmolarity because body fluids are NOT
  isoosmotic with the outside environment.
• Osmoregulator
• Body fluids are not isoosomotic with surroundings
• Enables animals to live in diverse environments
• Has an energy cost (active transport of solutes)

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COST OF OSMOREGULATION

• Depends on
• How different osmolarity is from the surroundings
• How easily water solutes move across the
  animals surface
• How much work is required to pump solutes across
  the membranes
• Ranges from 5 to 30 of total resting metabolic
  rate

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STENOHALINE VS. EURYHALINE

• Stenohaline narrow salt Most animals cannot
  tolerate substantial changes in external
  osmolarity
• Euryhaline broad salt Animals that can survive
  large fluctuations in external osmolarity.
• Examples Salmon, Talapia

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MARINE ANIMALS

• Most marine invertebrates are osmoconformers
• Marine vertebrates and some invertebrates are
  osmoregulators
• Ocean is strongly dehydrating because it is much
  saltier than than internal fluids and water is
  lost by osmosis
• Balance water loss by drinking large amounts of
  seawater
• Salt is actively pumped out of gills and passed
  through urine

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FRESHWATER ANIMALS

• Problems are opposite those of marine animals
• Freshwater animals are constantly gaining water
  by osmosis and losing salt by diffusion
• Maintain water balance by excreting large amounts
  of very dilute urine and taking in salt by the
  gills

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TEMPORARY WATERS

• Anhydrobiosis life without water animals can
  survive in a dormant state when their habitats
  dry up
• Water bears
• Survive for a decade or more in inactive state

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LAND ANIMALS

• Desiccation drying up is a huge problem for
  land animals
• Adaptations that help land animals avoid drying
  up
• Waxy layers of insects exoskeleton
• Shells of land snails
• Layers of dead keratinized skin
• Nocturnal
• Drinking and eating moist foods
• Using metabolic water (water produced during
  cellular respiration)

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44.2 NITROGENOUS WASTES

• When proteins and nucleic acids are broken down
  nitrogenous wastes are produced
• When these macromolecules are broken apart for
  energy ammonia (NH3) is produced which is very
  toxic
• Three forms of ammonia that animals secrete
• Ammonia
• Urea
• Uric acid

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AMMONIA

• Very soluble but only tolerated at low
  concentrations so must be released in lots of
  water
• Aquatic species (fish)

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UREA

• Substance produced in the vertebrate liver by
  metabolic cycle that combines ammonia with carbon
  dioxide
• System carries urea to kidneys where it is
  excreted
• Mammals, adult amphibians, sharks, marine bony
  fishes, turtles
• Advantage low toxicity and requires less water
• Disadvantage expend energy to produce it from
  ammonia

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URIC ACID

• Largely insoluble in water and can be excreted as
  a semi solid paste with very little water loss
• Insects, land snails, reptiles, birds
• Relatively non-toxic
• Requires considerable ATP to produce (more than
  Urea)

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EVOLUTION ENVIRONMENT ON WASTE

• Uric acid can be stored within the reptilian egg
  as a harmless solid left behind when the animal
  hatches
• Type of waste produced by vertebrates depends on
  habitat

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44.3 STEPS OF URINE PRODUCTION

• 1. Filtration body fluids are filtered to keep
  the good stuff in the body fluids and put the bad
  stuff in the filtrate
• 2. Reabsorption filtering the filtrate to make
  sure none of the good stuff is kept in the
  filtrate (active transport to reclaim valuable
  substances in body fluids)
• 3. Secretion filtering the body fluid to make
  sure all of the bad stuff is in the filtrate
• 4. Excretion filtrate leaves the body (urine)

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• Good stuff cells, proteins, large molecules,
  valuable solutes such as glucose,
• Bad stuff water, small solutes such as salts,
  sugars, amino acids, and nitrogenous wastes.
  Nonessential solutes and wastes

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SURVEY OF EXCRETORY SYSTEMS

• Protonephridia Flame-bulb system
• Flatworms
• Functions in osmoregulation (wastes diffuse out
  through body surface)

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• Metanephridia
• Annelids

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• Malpighian Tubules
• Insects and terrestrial arthropods

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• Vertebrate Kidneys
• Function in osmoregulation and excretion

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44.4 MAMMALIAN KIDNEY

• Site of water balance, salt regulation and
  excretion
• Pair of kidneys
• Each 10 cm long (kidney bean shaped)
• Supplied with blood by a renal artery and drained
  by a renal vein
• Urine exits through ureter and drains into
  urinary bladder
• Urine is excreted from urinary bladder through
  the urethra

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STRUCTURE FUNCTION OF NEPHRON

• 2 regions to the kidney
• Outer renal cortex
• Inner renal medulla
• Functional unit of the kidney is the nephron
  consists of single long tubule and a ball of
  capillaries called the glomerulus
• Bowmans capsule cup shaped swelling that
  surrounds the glomerulus
• Each human kidney contains a million nephrons

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• Filtration happens as blood pressure forces fluid
  from the blood in the glomerulus into the
  Bowmans capsule.
• Filtration is nonselective and filtrate contains
  salts, glucose, amino acids, vitamins,
  nitrogenous wastes and other small molecules
• Pathway of filtrate see figure 44.14

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• Between 1,100 to 2,000 L of blood flows through a
  pair of human kidneys each day.
• Nephrons process about 180 L of initial filtrate
• Nearly all sugar, vitamins, other organic
  nutrients and about 99 of the water are
  reabsorbed into the blood leaving only about 1.5
  L of urine to be voided per day
• 4 steps are completed in
• Proximal tubule
• Descending limbo of the loop of Henle
• Ascending limb of the loop of Henle
• Distal tubule
• Collecting duct

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44.5 WATER CONSERVATION IS A KEY TO TERRESTRIAL
ADAPTATION

• As the filtrate flows in the collecting duct past
  interstitial fluid of increasing osmolarity, more
  water moves out of the duct by osmois, thereby
  concentrating the solutes, including urea, that
  are left behind in the filtrate.

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REGULATION OF KIDNEY FUNCTION

• If a lot of salt is brought in with low water
  availability the mammal can excrete urea and salt
  with little water loss in hyperosmotic urine.
• If salt is scarce and fluid intake is high the
  kidney can get rid of the excess water with
  little salt loss by producing large volumes of
  hypoosmotic urine
• Regulated through nervous and hormonal controls
• ADH antidiuretic hormone
• RAAS renin-angiotensin-aldosterone system
• ANF atrial natriuretic factor

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• ADH is a response to an increase in the
  osmolarity of the blood when the body is
  dehydrated.
• RAAS responds when a situation that causes an
  excessive loss of both salt and body fluids
  (injury, severe diarrhea)

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44.6 DIVERSE ADAPTATIONS