Evolving for Harsh Ocean Conditions

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Evolving for Harsh Ocean Conditions Surviving
extreme temperatures, pressures, and salinity
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Water and Electrolyte Regulation

• How do organisms respond to changes between salt
  water, fresh water and terrestrial environments?

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I. Background on Solutions

• Solution is a liquid (solvent) with a solid
  (solute) dissolved in it.
• Semipermeable membrane allows certain molecules
  through (water, gas) while preventing the
  movement of others (solutes, salt, glucose)
• Osmosis is movement of water from high
  concentration to low concentration, across a
  semipermeable membrane

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• Active transport and facilitate diffusion are
  needed for solutes to pass across semipermeable
  membranes
• Organisms tend to maintain homeostasis.
• Semipermeable membranes keep body fluids of
  marine organisms separated from seawater and
  participates in vital exchange processes

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• Measurements
• Measured as conductivity (µS/cm, microsiemens),
  often expressed as parts per thousand solute.
• Osmotic pressure force that must be applied to a
  side of a semipermeable membrane to prevent water
  flow to that side.
• Osmolarity of osmoles in a solution.
• Osmoles Moles of solute in a solution that
  contribute to its tonicity.
• Tonicity a measure of the ability of a solution
  to exert pressure on a membrane

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• Categories of tonicity
• Isotonic or isoosmotic
• Equal osmolarity on both sides a of a
  semipermeable membrane
• Hypertonic or hyperosmotic
• High osmolarity, high salinity
• Water moves across semipermeable membrane into
  hypertonicity
• Results in cells loosing water and shrinking as
  they loose water (cells undergo crenation, or
  scalloping of membrane)
• Hypotonic or hypoosmotic
• Low osmolarity, low salinity
• Water moves away from hypotonicity, toward
  hypertonicity
• Results in cells explanding as they fill with
  water, and possible lysis

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II. Salinity Categories

• Brine is gt50 0/00 S
• (1L of sea water contains gt50g salts)
• Sea water is 30-50 0/00 S
• Brackish water range 0.5-30 0/00 S
• Freshwater is lt0.5 0/00 S

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III. Water and Salt Effects and Balance

• Osmoconformers- These organisms are isotonic with
  the environment. H2O loss is equal to H2O
  gained.
• These organisms are stenohaline having limited
  tolerance to salinity changes.
• Greek stenos narrow, close. Halos salt

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• Osmoregulators- despite external salinities, they
  maintain homeostasis by using osmoregluatory
  mechanisms
• These organisms are euryhaline and can tolerate a
  wide range of salt concentrations
• Many can move between sea and freshwater
  (esturine organisms) ex. Salmon
• Greek Eurys wide. Halos salt

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• Osmoregulatory Mechanisms
• Body fluids are 18 0/00 S
• In seawater
• H2O loss by osmosis (scales help reduce this)
• Organism drinks seawater
• Salt is excreted by chloride cells in gills
  (active transport)
• Kidneys produce small quantities of salty urine
• In freshwater
• H2O gain by osmosis (scales help reduce this)
• Salt absorbed by chloride cells in gills (active
  transport)
• Kidneys produce large volumes of dilute urine

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IV. Kidney Basics

• The greatest water and electrolyte regulator
• Kidney has two layers
• Outer cortex
• Contains proximal and distal convoluted tubules
• Inner medulla
• Contains Henles loop and collecting ducts

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• Nephron is the basic functional unit of a kidney
• Has two components
• Circulatory
• tubular
• Carries out 3 processes (filtration, absorption,
  and secretion)
• 1. Filtration
• Blood is filtered
• Plasma proteins remain in blood
• 2. Absorption
• From lumen of tubual
• Reabsorbed by blood (not all)

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• Tubular substance holds back large molecules that
  will not pass via gradient alone. They need
  factilitated diffusion, which is not available.
• Driving force out of capillary into tubule is
  blood pressure50mm Hg
• Net filtration pressure8mm Hg
• Driving force into capillary
• Plasmic osmotic pressure
• -non-filterable protein 32mm Hg
• Tubular pressure
• -tubular pressure 10mm Hg

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• Glomerular filtrate is the stuff filtered
• R _at_ which filtrate is formed is directly
  proportional to filtrate pressure
• The length, or presence, of Henles loop is
  dependent on a species water/salt retention needs.

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• 3. Tubular secretion
• Important in urine formation
• Transport mechanism becomes saturated from too
  much of a particular solute and are secreted

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• Excess H2O
• Increased urine production
• Pale colored with high water content (dilute)
• Increases blood volume??stroke volume??cardiac
  output??mean arterial pressure??blood pressure _at_
  glomerulus??filtration pressure??urine production

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• Lack of H2O
• Decreased production of normal urine (is
  concentrated)
• Decreases blood volume??stroke volume??cardiac
  output??mean arterial pressure??blood pressure _at_
  glomerulus??filtration pressure??filtrate
  formed??urine production
• Blood osmolarity increases (plasma osmolarity
  increases)
• Detected by neurosecretory cells of hypothalamus
• When stimulated, manufacture a chemical called
  vasopressin (ADH, Antidiuretic hormone, in most
  mammals)
• -Makes collecting ducts more permeable to
  H2O
• More H2O moves from collecting
  ducts to inner medulla
• gtsmall amounts of concentrated urine are
  produced

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• Excess salt
• ?Na ??plasma osmolarity??blood volume.
• Lack of salt
• ?Na??plasma osmolarity??blood volume
• Triggers secretion of aldosterone increases
  absorption of Na and H2O _at_ tubule
• increases secretion of K into blood. None
  is filtered into tubule
• -?K?alsosterone secretion?stimulates tubules
  to add K to filtrate?KIs removed in urine
• ?aldosterone caused retention of salt and water
  while promoting potassium excretion.
• FYI Aldosterone receptor blockers are used to
  treat low blood pressure

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• Osmoregulation summary

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V. Summary Applications

• Freshwater problems
• Water gain
• Solute loss
• Seawater problems
• Water loss
• Solute gain

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• Birds and reptiles
• Small glomerulus, less filtration, small amounts
  of concentrated urine
• Freshwater fish and amphibians
• Large glomerulus, no loop of Henle, large amounts
  of dilute urine
• Marine mammals
• Very small or absent glomerulus, no loop of
  Henle, very small amounts of urine
• Sharks
• Countercurrent flow in loops to concentrate
  salts, which are excreted as a hypertonic
  solution via rectal gland
• Marine birds and reptiles
• Nasal salt glands, hypertonic secretions (like
  tears) via counter-current multiplier mechanism

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• Marine fishes
• Nephron formation
• Urea retention increases osmolarity to decrease
  water problems
• Osmoconformers have no regulatory mechanisms
• Osmoregulators have active transport of Na and
  Cl-
• Chloride cells in gills (active transport of salt)

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• Mollusks and crustaceans
• Green glands are tubular structures and openings
  _at_ the base of antennae
• Filtration
• Absorption
• secretion