The Kidney

• Removal of urea from the blood
• Adjustment of ions in the blood
• Adjustment of water content in the blood

• First filtering the blood through ultrafiltration
• Then reabsorbing all the sugar, dissolved ions and as much water as the body needs.
• It then releases urea, excess water and ions as urine

Ultrafiltration:

• This is when a high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule.
• The membran between the blood vessels and the Bowman's capsule act like filters, so big molecules like protein and blood cells can not squeeze out. They stay in the blood.

Reabsorbtion:

• As the liquid flows along the nephron, useful substances are absorbed back into the blood.
• All the sugar is reabsorbed through the process of active transport, against the concentration gradient.
• Sufficient ions are reabsorbed by active transport, but excess ions are not.
• Sufficient water is reabsorbed. 

Release of Waste: The remaining substances (including urea) continue out of the nephron, into the ureter and down to the bladder as urine. 

• If the kidneys don't work properly, waste substances build up in the blood and you lose the ability to control the levels of ions and water in your body.
• You get problems in the heat, bones, nervous system, stomach, mouth etc
• Eventually this results in death
• People who suffer from kidney failure may be treated either by using a kidney dialysis machine or by having a healthy kidney transplant

• Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels, and removes waste substances.
• It has to carried out at regular intervals. 
• In a dialysis machine the person's blood flows between particularly permeable membranes, surrounded by dialysis fluid. 
• The dialysis fluid contains the same concentration of dissolved ions and glucose as healthy blood.
• This ensures that glucose and useful mineral ions are not lost.
• Only waste substances, such as urea and excess ions and water diffuse into the dialysis fluid.

Problems:

• Many patients have to have a dialysis session three times a week and each session takes 3-4 hours. This can be time consuming and inconfenient.
• Dialysis may cause blood clots or infections.

• Kidney transplants are the only cure to kidney diseases
• A disease kidney is replaced with a healthy one from a donor (alive or dead)
• However, the donor kidney maybe rejected. The recipient's antibodies may attack the antigens on the donor organ as they do not recognise them as part of the recipient's body.
• Antigens are proteins on the surface of cells.
• Precautions are taken to prevent rejection of the transplanted kidney:
  • A donor kidney with a 'tissue-type' similar to that of the recipient is used. The tissue type is based on antigens.
  • The recipient is treated with drug that suppress the immune system so it won't attack the transplanted kidney.

Kidney Dialysis machines are:

• Expensive to run
• Not pleasant experience
• Inconvenient

Transplants are:

• Cheaper
• Have long waiting lists
• Have possibility of rejection
• Drugs that suppress the immune system can make people vulnerable to other illnesses