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!

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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

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Kidney - Nephron

• Bowmans capsule is a cup-shaped capsule around
  the glomerulus to catch filtrate
• Renal corpuscle Glomerulus plus the Bowmans
  capsule since they function as a unit

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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

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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

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Key Points

• Define countercurrent.
• Look at the following picture and explain how
  countercurrent is advantageous.

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Kidney - Nephron

• Peritubular capillaries pick up substances being
  reabsorbed from renal tubules
• Common collecting tubule collects urine from all
  renal tubules

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Kidney

• Longitudinal kidney duct
• Carries urine to cloaca in all but placental
  mammals
• Various names for this duct depending on group

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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

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• Pronephros is the functional embyronic kidney in
  anamniotes

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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

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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

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Mammalian Vasa Efferentia Persistent
Mesonephric Duct
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Kidney Types

• Metanephros
• Caudal-most intermediate mesoderm
• Becomes the adult amniote kidney

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Kidney Types

• Metanephros adult amniote kidney
• Cortex outer region
• Medulla inner region
• Pyramids
• Papillae
• Pelvis slit-like funnel collecting urine from
  medulla

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Kidney Types

• Metanephros adult amniote kidney
• Ureter Metanephric duct
• Carries urine caudally

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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

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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

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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

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Urinary Bladder

• In mammals, the urinary bladder is drained by the
  URETHRA

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Urinary Bladder

• Functions
• Water reservoir except placental mammals
• Under ADH control
• Holding tank in placental mammales
• Pheromones
• Marking territory

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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?