Urinary System part 1

• Urinary system


  Comprises kidneys, ureters, urinary bladder, urethra

  
• Urinary organs


  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra

  
• Upper urinary tract


  Kidneys, ureters

  
• Lower urinary tract


  Urinary bladder, caudal ureters, urethra

  
• Kidneys


  • Lie retroperitoneally pressed against the dorsal abdominal wall on either side of the vertebral column
  • Located in the dorso-cranial part of the abdomen, in the lumbar region
  • Extend cranially under the last ribs into the intrathoracic part of the abdomen
• Right kidney position


  • Ventral to the last two-three ribs and first lumbar transverse process
• Left kidney position


  • Ventral to the last rib and first two or three lumbar transverse processes
• Right kidney


  • Cranial pole fits into a fossa of the liver, which helps fix its position
• Left kidney


  • More mobile and more likely to sag within the abdomen
• Kidney shape


  • Bean-shaped (dog, cat, goat, sheep, man)
  • Pyramidal-shaped (left)/Heart-shaped (right) (horse)
  • Flattened (pig)
  • Irregular oval-shaped ~ 12 lobes (cattle)
• Kidney consistency and colour


  • Firm
  • Reddish-brown
• Kidney lobation


  • Multilobar (pigs, large ruminant) - multipyramidal kidney with numerous medullary pyramids and papillae
  • Unilobar (Cats, dogs, horses, sheep, and goats) - fusion of the medullary pyramids - smooth surface with a single renal papilla
• Kidney surface, border, pole


  • Surface is generally smoothly convex
  • Medial border has an indentation region called the renal hilus - entry and exit site for structures
  • Cranial and caudal poles
• Perirenal fat


  • Covers the kidney in an adipose capsule, sometimes enough to hide the kidney completely
  • Protects against distorting pressures from neighbouring organs
• Renal capsule


  • Tough, fibrous capsule that encloses the kidney
  • Passes inward at the medial aspect to line the walls of the renal sinus
  • Restricts the kidney's ability to expand
• Kidney parenchyma


  • Divided into renal cortex and renal medulla
• Renal cortex


  • Reddish-brown colour and finely granular appearance
• Renal medulla


  • Consists of a dark outer zone and a paler red inner zone
  • In multilobar kidney, the medulla extends toward the renal calyx
  • In unilobar kidney, the renal medulla is fused
• Renal pyramids


  • Triangle structures in multilobar kidney that contain a dense network of nephrons
  • Bases are directed outward, toward the cortex
  • Apices project inwards and form renal papillae that fit into renal calyces
• Renal crest


  • Common papilla formed by the fused apices of the medullary pyramids in unilobar kidney
• Renal columns


  • Connective tissue extensions that radiate downward from the cortex through the medulla
• Renal pelvis


  • Urine collects here and the smooth muscle funnels the urine via peristalsis into the ureter
• Comparative anatomy of kidneys in domestic animals


  • Dog
  • Cattle
  • Small ruminants
  • Horse
  • Pig
  • Avian
• Dog kidney


  • Light brown colour
  • Smooth external surface
  • Bean-shaped, short and thick
  • Much perirenal fat
  • Shallow hilus
  • All renal pyramids fused into a single medullary mass with a common renal crest
• Cattle kidney


  • Brownish red colour
  • Lobated surface with 12-25 lobes of different sizes
  • No renal pelvis, papillae fit into calyces
  • Much perirenal fat
• Small ruminant kidney


  • Light brown colour
  • Smooth external surface
  • Bean-shaped, short, thick and almost circular
  • Much perirenal fat
  • Shallow hilus
  • Unipyramidal type with fused renal pyramids
• Horse kidney


  • Dark red to brown colour
  • Smooth external surface
  • Left kidney pyramidal-shaped, right kidney heart-shaped
  • Deep hilus
  • Small amount of perirenal fat
  • Unipyramidal type with fused renal pyramids
  • Yellowish mucus in renal pelvis
• Pig kidney


  • Grayish brown colour
  • Smooth external surface
  • Bean-shaped, flattened dorsoventrally with slightly pointed poles
  • Thick cortex, medulla only 1/2 to 2/3 thickness of cortex
  • Multipyramidal with numerous medullary pyramids and papillae
  • Papillae fit into renal calyces
  • Considerable perirenal fat
• Avian kidney


  • Brown colour
  • Elongated and divided into cranial, middle and caudal lobes
  • Left and right kidneys symmetrically placed on either side of vertebral column
  • Cortex and medulla not clearly demarcated, no renal pelvis
• Nephron


  • Basic functional unit of the kidney
  • Composed of renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule
• Renal corpuscle


  • Blood-filtering component of the nephron
  • Composed of glomerulus and Bowman's capsule
• Proximal convoluted tubule


  • Continuation of Bowman's capsule
  • Longest part of the nephron tubular system
  • Site of reabsorption and secretion
• Loop of Henle


  • Continues from proximal convoluted tubule, descends into medulla, makes U-turn, ascends back to cortex
• Distal convoluted tubule


  • Continuation of ascending loop of Henle
  • Drains into a collecting duct
• Collecting duct


  • Collects renal filtrate and transports it to renal calyx or pelvis
• Renal circulation


  • Renal artery branches into interlobar, arcuate, and interlobular arteries
  • Interlobular arteries divide into afferent arterioles supplying glomerular capillaries
  • Blood filtration, reabsorption, and urine excretion occur
• Distal convoluted tubule


  • Continuation of ascending loop of Henle
  • Drains into a collecting duct which transports filtrate to renal calyx/pelvis
• Renal circulation


  • Renal artery branches into interlobar, arcuate, interlobular arteries
  • Afferent arterioles supply blood to glomerular capillaries
  • Peritubular capillaries and vasa recta in medulla
• Blood filtration, reabsorption and urine excretion


  1. Blood enters kidney via renal artery, filtered in glomerular capillaries

  2. Small molecules, excess water, waste pass into Bowman's capsule, larger molecules stay in blood

  3. Filtered blood leaves kidney via renal vein