B3 3 Keeping internal conditions constant

3.1 Controlling internal conditions

• Keeping the body conditions within a narrow range is called HOMEOSTASIS  
• Conditions that must be controlled:
  • Temperature
  • Blood glucose
  • Water and ion content
  • Levels of waste products
• Waste products that have to be removed from body include:
  • Carbon dioxide - produced by respiration, removed via lungs when breathing out
  • Urea - Produced in liver from amino acid breakdown, removed by kidneys in urine, temporarily stored in the bladder
• If water / ion content is wrong then too much water may move into / out of cells damaging them

3.2 The human kidney

• A healthy kidney produces urine by:
  • First filtering the blood
  • reabsorbing all the sugar
  • reabsorbing the dissolved ions needed by the body
  • reabsorbing as much water as the body needs
  • releasing urea, excess ions and water in the urine
• UREA is removed from the blood by the kidneys during flitration

3.3 Dialysis - an artificial kidney

• People who suffer from kidney failure can be kept alive by dialysis.
• Treatment by dialysis restores the concentration of dissolved substances in the blood to normal levels and has to be carried out at regular intervals.
• In a dialysis machine a persons blood flows between partially permeable membranes. The dialysis fluid contains the same concentration of useful substances as the blood. This ensures that glucose and useful mineral ions are not lost. Urea diffuses out from the blood into the dialysis fluid.

3.4 Kidney Transplants

• In kidney transplants a…