Maintaining Water & Nitrogen Balance

Cards (18)

  • Water leaves the body via the lungs during exhalation
  • Water, ions, and urea are lost from the skin in sweat.
  • There is no control over water, ion, or urea loss by the lungs or skin
  • Excess water, ions, and urea are removed via the kidneys in the urine
  • If body cells lose or gain too much water by osmosis they do not function effectively.
  • The digestion of proteins from the diet results in excess amino acids which need to ne excreted safely. In the liver, these amino acids are deaminated for form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion.
  • The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions, and water.
  • the kidneys act as filters
  • Kidneys regulate ions
    1. Ions such as sodium taken into body in food
    2. Ions reabsorbed into blood
    3. If ion or water content wrong, balance between ions and water upset
    4. Too much or too little water drawn up by osmosis
    5. Wrong amount can damage cells or mean they don't work as well
  • Some ions are lost in sweat, but this amount is not regulated
  • Kidneys maintain right balance of ions
    1. Right amount of ions reabsorbed into blood after filtration
    2. Rest removed by body in urine
  • The water level in the body is controlled by the hormone ADH which acts on the kidney tubules. ADH is released by the pituitary gland when the blood is too concentrated and it causes more water to be reabsorbed back into the blood from the kidney tubules. This is controlled by negative feedback.
  • People who suffer from kidney failure may be treated by organ transplant or by using kidney dialysis.
  • dialysis has to be done regularly to keep the concentration of dissolved substances in the blood at normal levels, and to remove waste substances.
  • In a dialysis machine, the person's blood flows between partially permeable membranes, surrounded by dialysis fluid. It's permeable to things like waste substances but not big molecules like proteins.
  • The dialysis fluid has the same concentration of dissolved ions as healthy blood
  • This means that dissolved ions and glucose won't be lost rom the blood during dialysis.
  • Many patients with kidney failure have to attend dialysis sessions three times a week, witch each session taking 3-4 hours.