Removal of waste and water control

  • Created by: Hope
  • Created on: 16-03-14 17:45

Removal of waste and water control

The conditions inside our body must be very carefully controlled if the body is to function effectively. Waste is constantly being generated in the body and must be removed in order to stop waste levels becoming toxic. Water and mineral ion content must also be kept constant for our cells to work effectively. This is the role of the kidneys. Those who suffer from kidney failure cannot control their water and mineral ion levels, and must therefore undergo kidney dialysis or have a kidney transplant.

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Removing waste products

Waste products must be excreted. If they arent they will increase in concentration and may interfere with chemicall reactions or damage cells. 

Waste productWhy is it produced?How is it removed? Carbon dioxide It is a product of aerobic respiration Through the lungs when we breathe out Urea It is produced in the liver when excess amino acidsare broken down The kidneys remove it from the blood and make urine - which is temporarily stored in the bladder

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Water Balance

  • We take in water through food and drink, also we get some when we respire. 
  • We loose water in sweat, faeces, urine and when we breathe out. 

For our cells to work properly, our water and mineral ion content has to be maintained at the correct level - This is an example of homeostatis. If the ion and water content was to change to much water would be going in and out of the cells, then damaging them.

Our body must control the the water we take in and the water we lose. This is done by the kidneys

The kidneys maintain our water balance by producing urine of different concentrations

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Kidney Dialysis

Kidney dialysis the process by which toxic compounds from the blood are removed. (

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Kidney Dialysis 2

Patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and restore/maintain the water and ion balance of the blood.

A system for artifically 'cleaning the blood', removing urea and excess ions and water from the blood. 

a) Haemodialysis - A machine takes over the function of the kidneys. 

  • Blood is passed through a system of tubing made from a cellulose like substance that is partially permibale 
  • The tubing is surrounded by dialysis fluid - this contains glucose and useful minerals and has simialr concentrations to normal blood plasma

b) Peritoneal dialysis - the layer of tissue in the abdoment is used as the dialysis membrane 

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Kidney Transplants

  • The alternative to dialysis is to have a transplant
  • The main problem to kidney transplants is rejection.
  • The patients antigens could quickly send antibodies to the donated kidney to destory the kidney

Precautions against rejection

1) Tissue Typing- Only giving the kidney to patients who have antigens very similar to the donor kidney. - Long wait where patients would have to undergo dialysis during wait 

2) Immuno-suppressant drugs - Must be taken by patients for the rest of their lives. Supresses the immune system against attacking the donated kidney - Also supresses the immune system from attacking pathogens in the body, increasing risk of infections 

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Kidney Transplants Vs Kidney Dialysis

AdvantagesDisadvantages Kidney transplants

  • Patients can lead a more normal life without having to watch what they eat and drink
  • Cheaper for the NHS overall
  • Must take immune-suppressant drugs which increase the risk of infection
  • Shortage of organ donors
  • Kidney only lasts 8-9 years on average
  • Any operation carries risks

Kidney dialysis

  • Available to all kidney patients (no shortage)
  • No need for immune-suppressant drugs
  • Patient must limit their salt and protein intake between dialysis sessions
  • Expensive for the NHS
  • Regular dialysis sessions – impacts on the patient’s lifestyle
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