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Urinary System- Kidney

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					       Urinary System- Kidney
   Overall function
    – Osmoregulation (water, salt)
    – Nitrogenous waste in tetrapods
    – Ammonia in amphibians
    – Urea in mammals
    – Uric acid in birds and reptiles
    – Note: uric acid in birds is 3000x more
      concentrated than blood!
            Kidney - Nephron
 The functional unit of the kidney
 Filters blood to make urine
 Glomerulus is a network of permeable
  blood capillaries
    – Afferent glomerular arteriole
    – Efferent glomerular arteriole
         Kidney - Nephron
 Bowman’s capsule is a cup-shaped capsule
  around the glomerulus to catch filtrate
 Renal corpuscle – Glomerulus plus the
  Bowman’s capsule since they function as a
  unit
         Kidney - Nephron
 Renal Tubules
 Increase in complexity with higher
  vertebrates
 Function to secrete substances directly from
  blood to tubule
 Function for reabsorption from tubules back
  to bloodstream based on need
         Kidney - Nephron
 ADH = Antidiuretic hormone promotes
  water reabsorption from renal tubules
 Aldosterone – hormone that promotes
  sodium reabsorption from renal tubules and
  water passively follows
 Renal tubules are countercurrent for
  maximum efficiency
              Key Points
 Define countercurrent.
 Look at the following picture and explain
  how countercurrent is advantageous.
          Kidney - Nephron
 Peritubular capillaries pick up substances
  being reabsorbed from renal tubules
 Common collecting tubule collects urine
  from all renal tubules
                      Kidney
   Longitudinal kidney duct
    – Carries urine to cloaca in all but placental
      mammals
    – Various names for this duct depending on
      group
      Kidney Types based on
           Embryology
 Pronephros
 Forms from intermediate mesoderm
  (mesomere) very far cranially
 Renal tubules are temporary pronephric
  tubules
 Pronephric duct carries urine to cloaca
 Pronephric duct persists in anamniotes but
  changes its name to Mesonephric duct
   Pronephros is the functional embyronic
    kidney in anamniotes
            Kidney Types
 Mesonephros
 Middle region of intermediate mesoderm
 Longitudinal duct is Mesonephric duct (we
  called it archinephric duct in lab)
 Functional embryonic kidney in amniotes
 Adult kidney of anamniotes
               Kidney Types
   Mesonephros
    – Mesonephric tubules invade testes and form the
      Vasa efferentia which carry sperm from testicle
      to mesonephric duct
    – Mesonephric duct carries sperm & urine in
      anamniotes
    – Mesonephric duct in amniotes will only carry
      sperm & is called the Spermatic Duct or Vas
      Deferens
Mammalian Vasa Efferentia &
Persistent Mesonephric Duct
           Kidney Types
 Metanephros
 Caudal-most intermediate mesoderm
 Becomes the adult amniote kidney
                 Kidney Types
 Metanephros – adult amniote kidney
 Cortex –outer region
 Medulla – inner region
    – Pyramids
    – Papillae
   Pelvis – slit-like funnel collecting urine
    from medulla
           Kidney Types
 Metanephros – adult amniote kidney
 Ureter = Metanephric duct
 Carries urine caudally
          Urinary bladder
 Cyclostomes & Elasmobranchs have none
 Most fish have a widening of the
  mesonephric ducts that form the urinary
  bladder
 Dipnoans have a bladder that is an
  outpocketing of the cloaca
           Urinary Bladder
 Tetrapods have a urinary bladder that is an
  outpocketing of the cloaca
 The urinary bladder then empties into the
  cloaca in all except placental mammals
           Urinary Bladder
 The urinary bladder is formed from the
  embryonic membrane called the allantois
 The remnant of the allantois is called the
  urachus which becomes an umbilical
  ligament
             Urinary Bladder
   In mammals, the urinary bladder is drained
    by the URETHRA
             Urinary Bladder
   Functions:
    – Water reservoir except placental mammals
    – Under ADH control
    – Holding tank in placental mammales
    – Pheromones
    – Marking territory
              Key Points
 What are two roots that both mean kidney?
 Can you live without one kidney? Can you
  live without two? Why or why not?