Course 15.3Lesson 3 of 3

Kidney disorders, dialysis and transplant

When the kidneys fail, urea builds up in the blood. This lesson covers uraemia, kidney failure, kidney stones and the inflammation of the glomeruli, then shows how haemodialysis cleans the blood and why a transplant is the lasting treatment.

about 30 min1 simulation1 practice question

Lesson 3 of 3Show all lessons

Try the code and the simulations beside the lesson.

When the kidneys fail

The kidneys keep the blood clean. If they stop working well, the wastes stay in the blood, and the water and the salts of the body are no longer balanced. The common disorders are these.

Uraemia and renal failure

Malfunctioning of the kidneys can lead to the accumulation of urea in the blood. This is uraemia. It is highly harmful, and it may lead to kidney failure, also called renal failure, in which the kidneys no longer filter the blood.

An extra from physiology books: in acute renal failure the kidneys stop working suddenly, and may recover. In chronic renal failure they lose their work slowly over months or years.

Haemodialysis

The urea can be removed from the blood by a process called haemodialysis. It is done by an artificial kidney.

Blood is drained from a convenient artery and pumped into a dialysing unit. An anticoagulant, heparin, is added first, so that the blood does not clot.
The unit contains a coiled cellophane tube. The tube is surrounded by a dialysing fluid, which has the same composition as plasma, except for the nitrogenous wastes.
The porous cellophane membrane lets molecules pass according to the concentration gradient. Urea and the other wastes diffuse out of the blood into the fluid, because the fluid has none. Useful substances such as glucose do not leave, because the fluid has the same amount as the blood.
The cleared blood has anti-heparin added to it, and it is pumped back into the body through a vein.

This method is a boon for thousands of uraemic patients all over the world.

Dialysis in numbers

This part is a model, and it goes beyond the NEET syllabus text. Take a model of the body as one pool of 40 L of water. A dialyser clears 200 mL of blood of urea each minute. After 4 hours, about 70 per cent of the urea is gone, and about 30 per cent is left. A session of dialysis usually lasts 3 to 4 hours, and a patient needs it about three times a week. These values come from physiology books, and they differ for each patient.

A graph of the urea left in the blood, in per cent, against the time of dialysis in hours, from 0 to 6 hours. Three curves start at 100 per cent and fall, with the steepest fall for the largest dialyser clearance. The green curve is for a clearance of 100 millilitres a minute, the blue curve for 200 and the red curve for 300. A marked point on the blue curve shows that about 30 per cent of the urea is left after 4 hours. The title says that it is a one pool model for a body water of 40 litres.

Kidney transplantation

Kidney transplantation is the ultimate method in the correction of acute renal failure. This part is not in the NEET syllabus text, but NCERT prints it. A functioning kidney from a donor is used. The donor is preferably a close relative, to minimise the chance of rejection by the immune system of the host. Modern clinical procedures have raised the success rate of this complicated technique.

Renal calculi

Renal calculi are stones. A stone is an insoluble mass of crystallised salts, such as oxalates, that forms within the kidney. A stone can block the ureter, and then the flow of urine is stopped.

A drawing of a kidney, a ureter and the urinary bladder. Several grey stones lie in the renal pelvis of the kidney, and the note says that they are insoluble masses of crystallised salts such as oxalates. One stone lies in the ureter, and the note says that it blocks the flow of urine. One more stone lies in the bladder.

Glomerulonephritis

Glomerulonephritis is the inflammation of the glomeruli of the kidney. In general, inflammation of the kidney is called nephritis. The inflamed glomeruli filter badly. In physiology books, protein and blood can then appear in the urine.

Disorder	What happens
Uraemia	urea accumulates in the blood
Renal failure	the kidneys no longer filter the blood properly
Renal calculi	stones of crystallised salts form in the kidney
Glomerulonephritis	the glomeruli are inflamed

You should find that a larger clearance, or a longer time, removes more urea. The fall is quick at first and slow later, because less urea is left to be removed.

Try it in Python

The program uses the model to print the urea that is left after each hour of dialysis.

Practise with new numbers

Common mistakes

Saying that the dialysing fluid is pure water. It has the composition of plasma, without the nitrogenous wastes.
Saying that urea leaves the blood by active transport in the dialyser. It diffuses down its concentration gradient.
Adding heparin on the way back. Heparin is added before the unit. Anti-heparin is added after it.
Mixing up uraemia and glycosuria. Uraemia is urea in the blood. Glycosuria is glucose in the urine.
Saying that a kidney stone is a clot of blood. It is a mass of crystallised salts.

Remember these

Uraemia: urea in the blood, may lead to renal failure.
Haemodialysis: blood from an artery, heparin, a coiled cellophane tube in a dialysing fluid of plasma composition without nitrogenous wastes, diffusion by the concentration gradient, anti-heparin, return through a vein.
Transplant: a functioning kidney from a donor, preferably a close relative, to reduce rejection.
Renal calculi: stones of oxalates and other salts. Glomerulonephritis: inflamed glomeruli.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

What is uraemia, and why is it harmful?

Why is heparin added to the blood in haemodialysis, and anti-heparin later?

What is the composition of the dialysing fluid, and why?

What are renal calculi?

What is glomerulonephritis?

References

NCERT (2023). Biology, Textbook for Class XI, chapter 16, Excretory Products and Their Elimination.
Hall J. E. and Hall M. E. (2021). Guyton and Hall Textbook of Medical Physiology, 14th edition, Elsevier, the chapter on diuretics, kidney diseases and dialysis.
Daugirdas J. T., Blake P. G. and Ing T. S. (2015). Handbook of Dialysis, 5th edition, Wolters Kluwer, the chapters on the kinetics of urea.