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					            Chapter 25 Objectives

•   Understand homeostasis
•   Thermoregulation
•   Osmoregulation
•   Waste disposal
•   Human excretory system
•   Liver functions in waste disposal in humans
               Homeostasis

• “Steady-state” control mechanisms

• Only allow a narrow range of fluctuations in
  body conditions.

• Temperature – thermoregulation

• Water balance – osmoregulation

• Nitrogen wastes – excretion
            Thermoregulation

• Heat moves from hot areas to cold areas

• Animals can adjust body temperature

• Involves:
   – Heat production
   – Heat loss
   – Heat “gain”
           Thermoregulation – fig 25.1
• Conduction
  – Gain and loss
  – Direct from solid
    surface
• Convection
  – Gain and loss
  – Direct from liquid
    or air
• Radiation
  – Usually gain
  – Not direct
• Evaporation
  – Loss only
  – Indirect from liquid
    to gas exchange
Specific Examples of Thermoregulation

• Thermogenesis
  – Shivering
  – Non-shivering
• Sweating
• Insulation
  – Fat, fur, or feathers
• Blood flow
  – Dilation/Constriction
  – Countercurrent heat exchanger
             Thermoregulation

• Behavior can be used to regulate body
  temperature

  – Relocation

  – Migration

  – Bathing, wallowing etc….

  – Respiration
                  Thermoregulation
• Animals can change their metabolic rates
• Ectotherms can just allow themselves to
  “freeze”
  – Low energy requirementsbasically zero
    metabolism
  – Require glycerol to prevent water crystallization
• Endotherms need to maintain a higher body
  temperature that requires more energy
  – Torpor
  – Hibernation
  – Estivation
              Osmoregulation

• Metabolism depends on a precise balance
  of:
  – Water
  – Dissolved ions


• Unequal solute concentrations = osmosis or
  diffusion

• Cells cannot survive a net water loss or gain
              Osmoregulation
• Terrestrial animals are constantly losing
  water through evaporation and excretion

• Aquatic animals are exposed to continuous
  osmosis
  – Osmoconformer vs. osmoregulator
  – Salt water vs. fresh
              Osmoregulation

• Terrestrial animals cannot exchange
  materials directly with the environment

• Gain water by eating and drinking

• Land animals face a risk of dehydration
  – Water-proof covering
  – Reproductive system
  – Excretory system that conserves water
               Osmoregulation

• Sweating is used for thermoregulation

• Can be a problem for water loss
  – Salt loss can also cause problems, but usually
    not


• Drinking water is best when you’re
  sweating
           Seasonal Dehydration

• Seasonal environments often go from very
  wet to dry

• Some animals can lose large amounts of
  water and go dormant

  – Water loss should damage proteins and cell
    membranes

  – Use sugars to replace water
          Waste Disposal – fig 25.8

• Metabolism produces toxic by-products
  – Nitrogenous wastes


• Excreted wastes varies
  between species
• Amino groups form
  ammonia
• Aquatic animals
  – Ammonia excretion
     • Diffusion with no energy
         Waste Disposal – fig 25.8

• Terrestrial animals convert ammonia to less
  toxic products
  – Can be stored in the body
  – Requires energy


• Urea
  – Water soluble
• Uric acid
  – Crystal
  – More energy
                  Waste Disposal

• Kidneys
  –   80 km of tubules
  –   Network of capillaries
  –   Filters 1100-1200 L per day
  –   Produce 180 L of filtrate per day
       • Water, urea, ions, glucose, amino acids
  – Refine the filtrate
  – Excrete about 1.5 L of urine
Kidneys – fig 25.9
                Kidneys – fig 25.9

• Glomerulus
   – Blood pressure forces
     filtrate into glomerulus


• Nephron tubule
  refines the filtrate
   –   Proximal tubule
   –   Loop of Henle
   –   Distal tubule
   –   Collecting duct
      Nephron Function – fig 25.10

• Filtration

• Reabsorption

• Secretion

• Excretion
       Blood Filtration – fig 25.11

• Concentration gradient in the medulla

• Active & passive transport; secretion
                  Nephrons

• Nephrons conserve water

• Also maintain a tight balance of water and
  solutes

• Antidiuretic hormone (ADH)

  – Tells nephrons to absorb more water
              Liver Functions

• Prepares nitrogenous wastes for disposal
  – Synthesizes urea from ammonia

• Helps kidney get rid of
  other toxins

• Hepatic portal system

• Glycogen

				
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posted:4/20/2011
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