A machine for failed kidneys

The idea

An artificial kidney removes nitrogenous wastes by dialysis: blood passes through semi-permeable tubes in a dialysing fluid of the same osmotic pressure but without nitrogenous wastes, which diffuse out; unlike the kidney, it involves no re-absorption.

When kidneys fail

If both kidneys stop working, poisonous wastes build up in the body.

What could be done to clean the blood?

• Use a machine that removes the wastes
• Nothing can be done
• Wait for the wastes to go by themselves

Cleaning the blood

Press Next step. A doctor and a hospital do this in real life.

Dialysis

When the kidneys fail, an artificial kidney can clean the blood. The blood passes through tubes with a semi-permeable lining, inside a tank of dialysing fluid. The fluid has the same osmotic pressure as blood but no nitrogenous wastes, so the wastes diffuse out of the blood into it. The cleaned blood goes back to the patient. Unlike a real kidney, there is no re-absorption.

An artificial kidney removes nitrogenous wastes by dialysis: blood passes through semi-permeable tubes in a dialysing fluid of the same osmotic pressure but without nitrogenous wastes, which diffuse out; unlike the kidney, it involves no re-absorption.

Notes

An artificial kidney removes nitrogenous wastes from blood by dialysis (blood in semi-permeable tubes in dialysing fluid without wastes); unlike the kidney, no re-absorption.

Check yourself

Why does the dialysing fluid contain no nitrogenous wastes?

How do the wastes leave the blood in an artificial kidney?

How does an artificial kidney differ from a natural kidney?

When can an artificial kidney be used?

• So that the wastes from the blood can diffuse into it — correct. Yes!
• So that glucose can be re-absorbed. There is no re-absorption involved in an artificial kidney.
• So that its osmotic pressure is different from blood. The dialysing fluid has the same osmotic pressure as blood.
• They are collected by Bowman's capsule. Bowman's capsule is part of the nephron in a natural kidney.
• They pass into the dialysing fluid by diffusion — correct. Yes!
• They are re-absorbed back into the blood. The wastes pass out of the blood; there is no re-absorption in an artificial kidney.
• It does not remove nitrogenous wastes. It is a device to remove nitrogenous waste products from the blood through dialysis.
• It makes the blood poisonous. It purifies the blood, which is pumped back into the patient.
• There is no re-absorption involved — correct. Yes!
• In case of kidney failure — correct. Yes!
• When the kidneys are working well. It is used in kidney failure, when the activity of the kidneys is reduced.
• To digest food. Digestion is done in the alimentary canal; the artificial kidney removes nitrogenous wastes from the blood.