Urine Information

• Urine information


  1. Glomerular filtration

  2. Selected reabsorption

  3. Tubular secretion
• Function of the kidneys

  • Rid the body of wastes (especially nitrogenous wastes i.e. urea, uric acid and creatinine)
  • Regulate the balance of fluid, salt and pH
• Filtration


  Process of filtering the blood
• Glomerular Filtration


  1. Occurs in renal corpuscle

  2. Afferent arteriole wider than efferent - high pressure forces fluid out of capillary into capsule

  3. All material except cells and plasma proteins

  4. Capillary wall and wall of capsule are 1 cell thick

  5. Fluid in capsule = filtrate
• Selective Reabsorption


  1. Much of what is filtered in capsule is useful to the body

  2. Selective reabsorption of filtrate occurs to return them to blood (peritubular capillaries)

  3. Water

  4. Glucose

  5. Amino acids

  6. Ions (sodium, potassium, calcium, chloride, bicarbonate)

  7. Reabsorbed by cells lining renal tubule (proximal convoluted tubule, loop of Henle, distal convolute tubule and collecting duct

  8. Requires large surface area (long length of renal tubule and large number of nephrons
• Reabsorption - Proximal convoluted tubule (PCT)


  • Water (passive, osmosis)
  • Glucose (active)
  • Amino Acids (active)
  • Vitamins (passive)
  • Potassium, Chloride, Bicarbonate ions (passive)
  • Sodium (active)
• Reabsorption - Loop of Henle


  Sodium ions (active)
• Reabsorption - Distal convoluted tubule (DCT)

  • Sodium ions (active)
  • Potassium, Chloride ions (passive)
  • Water (active, uses hormone, dependent on body's need) in descending loop only
• Reabsorption - Collecting duct


  Water (active, uses hormone, dependent of body's need)
• Tubular Secretion


  1. Adds materials to filtrate from blood:

  2. Potassium ions (K+)

  3. Hydrogen ions (H+)

  4. Creatinine

  5. Ammonium ions (NH4+)

  6. Some drugs (penicillin)
• Main effects of Tubular Secretion

  • Maintain blood pH: (7.4-7.5) raises by removing H+ & NH4+
  • Maintain urine pH: (6) slightly acidic by presence of H+ & NH4+
• Urine Excretion


  1. Substances not reabsorbed drain form the collecting ducts into the renal pelvis

  2. Fluid is now called urine

  3. Urine drains into ureters

  4. Muscle contractions push urine into bladder for storage

  5. Urethra carries urine from bladder out of body
• The bladder


  • Has elastic walls
  • Can stretch to hold maximum of 750 mL
  • Voiding of urine triggered by stretch receptors
  • Two sphincter muscles control exit of urine
  • Sphincter muscles under voluntary and involuntary control
  • Control is a learned process
  • The release of urine from the body is termed Micturition / Micturating
• Waste products need to be in solution to be removed and so necessitate a certain amount of water loss
• Approximately 500 mL of water has to be filtered out of the blood per day to remove metabolic wastes
• When water content of the body fluids is low, the urine that is excreted is very concentrated
• When water content of the body fluids is high, the urine that is excreted is very dilute
• On average a healthy person produces around 1.5 L of urine per day