Zoology 484----------------------November, 1997-------------------------------M.P.Wenderoth

Osmoregulation and Excretion

Readings: Randall Chapter 14 pp. 571-588, 608-619

Osmoregulation

Regulation of salt and water balance of the animal body

Excretion

Removal of nitrogenous waste products from the body

Problems of Osmoregulation

Osmosis-- movement of solvent (water) down its concentration gradient

Osmolarity-- number of solutes (particles) dissolved in the solvent.

Animal Body--

• Intracellular fluid (ICF) -------.9%- 3.5%-----------300 - 1000mOsm
• Extracellular fluid (ECF) ------.9%- 3.5%-----------300 - 1000mOsm

Environment

• Marine -sea water-(SW)-----3.5% salinity--------1000 mOsm
• Brackish------------------------ .5 to 3.0%
• Freshwater (FW)--------------.5% salinity---------- 1-50 mOsm
• Terrestrial

Osmotic Stress between the ECF of animal and the environment

• 1000mOsm animal in SW ----at equilibrium
• 300 m Osm animal in SW ----water loss and salt gain
• 300mOsm animal in FW ----water gain and salt loss

Osmoregulatory Mechanisms

regulate osmotic pressure and ion concentration of extracellular fluid (ECF) of body

Organs of osmoregulation--specialized epithelial tissue

• kidneys,
• gills,
• skin,
• Malpighian tubules,
• salt glands
• rectal glands,
• intestines,
• antenneal glands

How animals handle osmotic stress

• osmoregulators-maintain strict extracellular osmotic homeostasis
• osmoconformers-cells can tolerate osmotic changes
  • use of organic osmolytes to regulate cell volume
• aquatic environments
  • stenohaline--can only handle a narrow range of salinity
  • euryhaline-- can handle a wide range of salinity

Factors that impact salt and water balance of the animal

• 1. Gradient between animal and environment
• 2. Surface to volume ratio (greater for small animals)
• 3. Permeability of Integument
• 4. Feeding and drinking behavior
• 5. Temperature regulation (big problem for endotherms)
• 6. Removal of nitogenous waste (solubility of waste product)

  Life in the Water

  Invertebrates

  • most are osmoconformers
  • some are osmoregulators
    ex. -- crayfish (300 mOsm) in FW (50 mOsm)
    • water gain -----dilute urine---- produced by antenneal gland
    • salt loss --------active transport at gills

  Vertebrates ( Or how Kevin Costner made it in Waterworld)

  • Elasmobranchs in SW
    • maintain normal salt concentration but are hyperosmotic to SW ---HOW?----reduce the gradient with Urea and TMAO
  • Teleosts in SW
    • Problem: water loss- salt load
    • Solution: kidneys liability- scant isotonic urine to remove Mg2+ and SO42-
    • chloride cells of gills to actively transport Na and Cl out of body
    • drink sea water and eat sea food (sushi!)
  • Teleosts in FW
    • Problem: water gain --- salt loss
    • solution: Integument permeability
    • dilute urine-- do not drink water-
    • chloride cells of gills, eat osmoregulators, dilute urine

    Anadromous fish

    Catadromous fish

    role of hormone in regulating chloride cells of these fish

  • Amphibians in FW
    • Problem: water gain and salt loss
    • Solution: copious dilute urine
    • active uptake of Na from environment by Skin
  • Reptiles (air breathers--no gills) in SW
    • Problem: high salt load in food and drink
    • solution: low permeability of integument
    • kidney -- only isotoninc urine
    • salt glands

  Nitrogen Excretion

  Removal of nitrogenous waste

  ammonia---------------urea---------------uric acid

  • number of nitrogens each contains
  • solubility
  • toxicity
  • amount of water required for removal from body
  • animals that use each form

    Life on Land-

    - (How not to desicate and wind up an exhibit at Ye Olde Curiousity Shoppe) -

    Oxygen plentiful but evaporation a constant threat

    Two environments

    • Humid
      • moist skinned animals: earthworms and amphibians
    • Dry (Xeric)
      • Lipid layer of integument-- arthropods and vertebrates

    Water balance

    • loss-- evaporation from skin, lungs, gills and urine, feces
    • gain--ingested food, drink; skin, gills, metabolic water

    Invertebrates ----Arthropods---osmoregulators but ectotherms

    • Problem: water loss to environment via evaporation
    • Solution: Waxy epicuticle
    • Malpighian tubules can produce hypertonic urine

    Physiology and anatomy of Malpighian tubule

    Vertebrates

    • Reptiles---problem: desication
      • Kidney--scant isotonic urine
      • Cloaca -- resorbs water
      • Nitrogen waste--uric acid
    • Avian--- marine environment
      • Problem: salt load from drinking salt water
      • solution: Kidneys make a 2X urine
      • salt gland
      • Anatomy and Physiology of salt gland
    • Mammals--
    • problem: desiccation and urea production
    • solution: drink water if possible
    • kidneys produce 6-30 X urine

    Special examples

    • Kangaroo rat
    • Kangaroo rat picture
    • Camel
    • camel facts

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