Kidneys

• the kidneys are organs which control the levels of ions and water in the blood
• the kidneys act as filters to clean the blood
• functions of the kidneys

  • regulate blood water levels
  • reabsorb useful substances into the blood
  • adjust levels of salts and ions into the blood
  • excretion of urea and other metabolic wastes
• process of kidneys

  • blood enters kidney via the renal artery
  • it is put under pressure so that small molecules are forced out of the capillaries
  • kidneys selectively reabsorb certain molecules to maintain the correct levels in the blood
  • molecules not absorbed make up urea which leaves through ureter
  • urine goes to bladder where its stored then released
  • blood leaves kidney via renal vein
• substances removed from body in urine

  • urea
  • ions
  • water
• urea

  • proteins that cant be stored by the body so excess amino acids are converted into fats/carbohydrates
  • occurs in liver through deamination
  • ammonia is a waste product which is produced and is toxic so converted to urea
• ions

  • taken into the body in food then absorbed into the blood
  • if the ion content is wrong it could upset the balance
  • some ions are lost in sweat
• water

  • body has to constantly balance the amount of water coming in or out
  • lose water by sweating and breathing
• if water content levels increases...

  • receptors in the brain detect an increase in water content
  • the pituitary gland receives the information and co-ordinates a response
  • pituitary gland releases ADH
  • kidneys reabsorb less water & urine becomes more dilute
• if water content levels decreases...

  • receptors in brain detect decrease in water content
  • the pituitary gland receives the information and co-ordinates a response
  • pituitary gland releases more ADH
  • kidneys reabsorb more water & urine becomes more concentrated
• water regulation is an example of negative feedback because it releases hormones to bring water levels to normal when its either too concentrated or too dilute
• kidney failure is caused when waste substances build up in the blood and you lose the ability to control levels of water and ions
• dialysis machines filter the blood
• dialysis fluids have the same concentration of sodium and glucose as blood plasma so there is no overall lost and only waste substances are removed
• dialysis has to be done regularly to keep concentration of dissolved substances in blood at normal levels and to also remove waste substances
• kidney transplant

  • advantages - normal lifestyle, cheaper, dont need dialysis
  • disadvantages - shortage of organ donors, risk of failure/rejection from body, only lasts 8-9 years
• dialysis

  • advantages - facilities widely available, trained professionals at all times, no need for equipment at home
  • disadvantages - strict diet & fluid limits, take more medications, takes a long time