Kidneys

• 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 urine
• If body cells lose or gain too much water by osmosis they do not function efficiently
• The digestion of proteins from the diet results in excess amino acids which need to be excreted safely. In the liver these amino acids are deaminated to 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
• ADH stands for anti-diuretic hormone
• ADH is released from the pituitary gland and monitors the water content of the blood
• When water content is high

  • Pituitary gland releases less ADH
  • Less water is reabsorbed by the kidney tubules
  • Less concentrated, high volume urine
• When water content is low

  • Pituitary gland releases more ADH
  • More water is reabsorbed by the kidney tubules
  • More concentrated, low volume urine
• When both kidneys fail dialysis or and organ transplant are needed
• Dialysis machines have the patients blood flowing through a partially permeable membrane and the dialysis fluid contains a healthy concentration of ions and glucose so only waste (urea), excess ions and water diffuse across the barrier
• Negatives of dialysis

  • Expensive for NHS to run
  • Can cause blood clots and infections
  • Has to be done multiple times a week
• Negatives of kidney transplants

  • Patient has to be on immunosuppressant drugs which can make them more liable to illnesses
  • Very long waiting list