Urinary system

• Function of Kidney


  • Production of renin to maintain blood pressure
  • Production of erythropoietin to stimulate red blood cell production
  • Conversion of vitamin D to its active form
• The right kidney is slightly lower than the left
• An adult kidney is about 12 cm (5 in) long and 6 cm (2.5 in) wide
• Renal hilum


  A medial indentation where several structures enter or exit the kidney (ureters, renal blood vessels, and nerves)
• An adrenal gland sits atop each kidney
• Fibrous capsule


  Encloses each kidney
• Perirenal fat capsule


  Surrounds the kidney and cushions against blows
• Renal fascia


  The most superficial layer that anchors the kidney and adrenal gland to surrounding structures
• Renal cortex


  Outer Region
• Renal medulla


  Deeper Region
• Renal pyramid


  Triangular regions of tissue in the medulla
• Renal column


  Extensions of cortex like material that separate the pyramids
• Renal pelvis


  Medial region that is a flat, funnel-shaped tube
• Calyces


  Cup-shaped "drains" that enclose the renal pyramids
• Calyces


  Collect urine and send it to the renal pelvis, on to the ureter, and to the urinary bladder for storage
• Each kidney contains over a million nephrons
• Glomerulus


  A knot of capillaries made of podocytes
• Podocytes


  Make up the inner (visceral) layer of the glomerular capsule
• Glomerular capsule


  A cup-shaped structure that surrounds the glomerulus. First part of the renal tubule
• Types of nephrons

  • Cortical nephrons
  • Juxtamedullary nephrons
• Cortical nephrons


  Located entirely in the cortex, include most nephrons
• Juxtamedullary nephrons


  Found at the cortex-medulla junction, nephron loop dips deep into the medulla
• Collecting ducts

  Collect urine from both types of nephrons, through the renal pyramids, to the calyces, and then to the renal pelvis
• Afferent arteriole


  Arises from a cortical radiate artery and feeds the glomerulus
• Efferent arteriole


  Receives blood that has passed through the glomerulus
• High pressure forces fluid and solutes out of blood and into the glomerular capsule
• Renal artery


  Provides each kidney with arterial blood supply
• Renal vein


  Returns blood to the inferior vena cava
• Renal tubule


  Extends from glomerular capsule and ends when it empties into the collecting duct
• One-quarter of the total blood supply of the body passes through the kidneys each minute
• If arterial blood pressure is too low

  Filtrate formation stops
• Filtration


  A nonselective passive process
• Peritubular capillaries


  Reabsorb useful substances from the renal tubule
• Most reabsorption

  Occurs in the proximal convoluted tubule
• Materials left in the renal tubule

  Move toward the ureter
• Urea


  End product of protein breakdown
• Uric acid


  Results from nucleic acid metabolism
• Creatinine


  Associated with creatine metabolism in muscles
• In 24 hours, about 1.0 to 1.8 liters of urine are produced
• Filtrate contains everything that blood plasma does (except proteins)