Animal Physiology – Osmoregulation Excretion

							   Animal Physiology –
Osmoregulation & Excretion
                   Temperature Regulation

 Ectotherm – heated from the outside
   Closest to cold-blooded

 Poikilotherm – Body temp. same as the outside
   Fish have body temp same as the outside

   They seek a region of water with optimal temperature and
    remain there
 Homeotherm
   Maintain constant body temperature
         Even if the environmental temperature fluctuates
     Synonym for endoderm
     Only birds & mammals
                Homeotherms (Page 2)

 Usually maintain a body temp higher than
  surroundings
 Large animals = large internal environment = easier
  to maintain internal environment =
      -- More likely to be homeothermic
 Homeothermy is energy expensive
    Glucose oxidation (known as what?) is source of energy
    Humans, 60% of nutritional intake goes to provide body heat
    Homeotherms metabolic rate greatly exceeds that of
     ectotherms
    Therefore, they must consume significantly more nutrition
                Homeotherms (Page 3)

 Homeotherms consume more nutrition, eat more
 often, and digest food faster than ectotherms

 For terrestrial animals, homeothermy is thought to
 have conferred an advantage as it allows these
 organisms to be active at any time
    The dominant animal at the time was the reptile (ectotherm)
    Homeothermy made it possible to invade other lands (colder
     environments) when competition for temperate land was too
     great
    Some scientists believe that dinosaurs were homeotherms
Terrestrial Temperature Fluctuates
              Problems of Terrestrial Life

 Temperature on land fluctuate significantly
   At the intersection of land and water, we even have a special
    name for this difference: sea breeze


 Hence, temperature regulation is important for
  animals living on land
 Also, terrestrial organisms must also be concerned
  with water conservation
 On land, we may also find a north-south cline
     Difference across a geographic range
         One Strategy of Temp. Regulation

 Coutercurrent Exchange – helps to warm or cool
 extremities
    Blood veins & arteries lies next to each other
    Example: Warm core blood flows into the paw
      of a polar bear in frigid
     water, which warms the
     blood returning from
     the paw
                      Osmoregulation

 Def – MGT of body’s water & solute concentration
 Osmoregulation depends on the environment the
 organisms lives in

 Marine Vertebrates (Fish) – face dehydration
 pressures from the sea (salt H2O)
    So they are in a hypertonic solution
    What happens to H2O inside the fish? – Exits
    Fish lose great amounts of water via gills & skin
    To combat this loss, fish produce little urine & consume large
     amounts of sea H2O combined with active transport of salts
              Osmoregulation (Page 2)

 Freshwater vertebrates (fish)
   Environment is hypotonic, so need to counter osmotic
    pressure
   Active transport of salts into body

   Excrete substantial amounts of dilute urine
                          Excretion

 Terrestrial Organisms
   Evolved mechanisms that expel wastes into the environment &
    retain water as well
   Different organisms = different mechanisms
     Protista = Contractile vacuole
     Platyhelminths = Flame cells
     Earthworm = Nephridia
     Insects = Malpighian Tubules
     Humans = Nephrons (Kidneys)
                    Excretion (Page 2)

 Def – removal of metabolic wastes
   Wastes include:
     CO2 & H2O (Respiration wastes)
     Nitrogenous waste (from protein metabolism)



 Nitrogenous wastes types:
   Ammonia, urea, or uric acid



 Excretion Organs (Humans)
   Skin, lungs, kidneys, & liver (site of urea production)
                  Nitrogenous Wastes

 Ammonia
   Highly toxic, but water soluble
   Generally excreted by waterborne organisms

 Urea
   Not as toxic as ammonia
   Humans & Earthworms excrete
   In mammals, ammonia is decomposed into urea in liver

 Uric Acid
   Pastelike substance that you have seen on the outside of your
    car
   NOT water soluble; Least toxic form
   Deposited by birds (and reptiles) – minimum of H2O loss
                          Human Kidney

 Dual functionality: Osmoregulation & Excretion
 Renal = kidney
     Renal vein, renal artery, renal nerve, renal failure
 Kidneys are the body’s filters
 Kidneys filter 1,000 – 2,000 L blood per day
 Produce 1.5 L urine per day
 Humans need to conserve water, but also remove toxins
 Kidney adjusts volume & concentration of urine due to
  animal’s intake of water & salt
     Fluid intake is high & salt intake low = dilute (hyposmotic) urine
     Fluid intake low & salt intake high = conc. (hyperosmotic) urine
Human Kidney
                      The Nephron

 Functional unit of the kidney
 Consists of
   Capillary clusters

   Glomerulus (located inside Bowman’s Capsule)

   Renal tube long narrow tube

 Each kidney contains ~1 million nephrons
 Nephron has 4 stages:
   Filtration

   Secretion

   Reabsorption

   Excretion
                            Nephron Steps

 Filtration
   Passive (diffusion) & nonselective
   Blood pressure forces fluid from the glomerulus into the
    Bowman’s Capsule
   Bowman’s Capsule contains specialized cells which increase
    the rate of filtration
   Anything small enough to filter out does so
         Glucose, salts, vitamins, wastes such as urea, other small
          molecules
     From Bowman’s Capsule, the filtrate travels to the proximal
      tubule, the loop of Henle, distal tubule, then to the collecting
      duct or tubule
     From the collecting tubule, filtrate trickles into the ureter
      & finally the urinary bladder (temp storage)  Urethra  out
               Nephron Steps (Page 2)

 Secretion
   Active & Selective

   Uptake of molecules that did not get filtered into Bowman’s
    Capsule
   Occurs in Proximal & distal tubules

 Reabsorption
   Water & solutes (glucose, amino acids, & vitamins) that
    entered the tubule during filtration are returned to
    peritubular capillaries then to the body
   Proximal tubule, Loop of Henle, and to collecting tubule
                   Nephron (Page 3)

Loop of Henle – Acts as a countercurrent exchange mechanism
   Maintains a steep salt gradient surrounding the loop
   This gradient ensures that water will continue flowing out of
    collecting tubule of the nephron
   Creates hypertonic urine
   Conserves water
   Longer Loop of Henle = More water reabsorption



Excretion
   Removal of metabolic wastes (nitrogenous wastes)
   Everything that passed into the collecting tubule is excreted from
    the body
Kidney Dialysis
-- When the kidney(s) fail,
patients must undergo
dialysis (artificial
mechanical filtration)
                        Nephron Particulars

 Renal Cortex
   Glomerulus – tightly packed ball of capillaries

   Bowman’s Capsule – encapsulates the glomerulus
         Actual site of blood filtration
     Proximal Tubule – site of substantial secretion & absorption
     Distal Tubule – another important site of secretion &
      absorption
           Nephron Particulars (Page 2)

 Renal Medulla
   Loop of Henle
     Descending limb – Impermeable to Salt, but permeable to water
       Filtrate becomes increasingly concentrated

     Ascending limb – Impermeable to water, but permeable to Salt
       NaCl diffuses out of the lower part, increasing salt concentration
        of the surrounding tissue
           Nephron Particulars (Page 3)

   Collecting Duct
     Carries the remaining filtrate through tissue that has high
      osmolarity (salt concentration)
     ADH (Anti-Duretic Hormone) – Determines whether water is
      removed here or not
       If ADH is present, collecting ducts become permeable to water
        & filtrate = hypertonic urine
       If ADH is NOT present, collecting ducts’ walls remain
        impermeable to water = hypotonic urine
          Hormonal Control of Kidneys

 Under the control of Nervous & Endocrine systems
 Hence, kidney can quickly respond to the changing
  requirements of the body

 ADH (Anti-Diuretic Hormone)
   Produced by the hypothalamus
   Stored in the Posterior Pituitary
   Targets the collecting tubule of the nephron
   Hypothalamus has osmoreceptor cells that monitor blood
    concentrations of salts
   On a feedback loop to maintain homeostasis of fluid
    concentration
                           ADH @ Work

 When body’s salt concentration is too HIGH, ADH is
 released into the blood
    ADH increases permeability of the collecting tubule
        So more water is collected from the urine, and urine volume is
         decreased
 When body’s salt concentration is too LOW (dilute),
 due to water intake being too high or salt intake too
 low, ADH is reduced = more urine production

 EtOH = ADH inhibition = excessive urine production
   May lead to dehydration