URINE FORMATION

• 3 processes of urine formation:

  • Glomerular filtration
  • Tubular reabsorption
  • Tubular secretion
• Glomerular filtration:

  • Water and solutes are forced through glomerular walls while proteins and blood cells are too large to pass through filtration.
  • Filtrate leaves via renal tubule.
• Tubular reabsorption:

  • Peritubular capillaries reabsorb useful substances such as water, glucose, amino acids, and ions.
  • Occurs in PCT
  • Some reabsorption is passive, but most is active
• Tubular secretion:

  • Eliminates wastes such as H, Na, and K ions, nitrogenous wastes (urea, uric acid, creatinine), ammonia, and bicarbonate ions
• 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 to 1.8 liters of urine are produced
• Filtrate - contains the same elements as blood plasma except proteins
• Urine - what remains after filtrate has undergone reabsorption
• Urochrome - the pigment responsible for the yellow color of urine and is formed by the destruction of hemoglobin
• Urine has a pH of 6, and a specific gravity of 1.001 to 1.035.
• Solutes that are not normally found in urine (with name of condition):

  • Glucose (glycosuria)
  • Blood proteins (proteinuria)
  • RBCs (hematuria)
  • Hemoglobin (hemoglobinuria)
  • WBCs (pus) (pyuria)
  • Bile (bilirubinuria)