Maintaining water and nitrogen balance in the body

• What is osmosis?

  movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• In what ways is water lost from the body?

  • during exhalation via the lungs
  • sweating
  • urine (some reabsorbed in the kidney)
• in what ways are ions lost from the body?

  • Sweating
  • urine
• How are excess amino acids excreted from the body?

  • excess amino acids are deaminated in the liver to form ammonia
  • ammonia is toxic, therefore converted into urea
  • urea is excreted from the body via sweat and urine
• How do kidneys maintain the balance of water and other substances in the body?

  • filter blood in order to remove waste products
  • selectively reabsorb useful molecules
• Full name of ADH hormone

  Anti-diuretic hormone
• Where is ADH secreted in the body?

  Pituitary gland of the brain
• How does ADH affect the reabsorption of water in the kidneys

  • when the blood is too concentrated, the pituitary gland secretes more ADH
  • ADH travels in the bloodstream to the kidney and increases the permeability of kidney tubules to water
  • more water is reabsorbed in the kidneys, resulting in a smaller volume of more concentrated urine
• Why is kidney failure dangerous?

  • when damaged, unable to filter the blood properly
  • a build-up of toxic molecules in the body
  • uncontrolled ion and water balance and cells being damaged as a result of osmosis
• Two main ways of treating kidney failure

  • dialysis
  • transplant
• What is kidney dialysis?

  • use of a specialist machine to carry out the same function of kidneys
  • dialysis fluid contains the same concentration of glucose and ions as healthy blood
  • as a result, only excess and waste molecules are lost from the blood, and glucose and ions remain