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Kidney dialysis and transplantation

Explain repeated dialysis support and compare it with a donor kidney, including the need for ongoing care and the risk of tissue rejection.

  • SEC G1 Science 2027

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What job needs support?

Kidneys remove waste products and excess water from the blood and help keep its salt balance suitable for the body. The removed substances leave in urine. If kidney function is severely reduced, wastes and excess water can build up. A useful comparison starts with that missing job, then asks how a technology supports it.

Dialysis supports some kidney functions

Dialysis removes wastes and excess water from blood. One form, haemodialysis, passes blood through a filter outside the body and returns the filtered blood. The removed wastes and water are not returned with it. Another form uses a lining inside the abdomen as an exchange surface; not all dialysis involves blood leaving the body.

Dialysis does not repair the kidneys or replace every kidney function. The body keeps producing wastes between treatments, so sessions need to be repeated. With continuing kidney failure, this dependence may be lifelong unless kidney function recovers or a successful transplant becomes possible. The repeated treatment, time and access to equipment are limitations even when dialysis is helping.

A transplant replaces an organ

A kidney transplant places a donor kidney inside the body. A functioning donor kidney can filter blood and make urine, restoring much kidney function. A suitable donor and surgery are needed, followed by ongoing care.

The immune system may recognise donated tissue as foreign and attack it. This is tissue rejection, which can damage the donor kidney. Medicines that suppress the immune response reduce rejection risk, but ongoing care is still needed. A transplant is not a guaranteed one-time cure.

Two ways to support failed kidney functionOn the left, haemodialysis takes blood from the body through an external filter and returns the filtered blood. Wastes and excess water are removed separately. On the right, a donor kidney inside the body filters blood and produces urine. Dialysis requires repeated sessions; transplantation requires a donor and ongoing care and carries a risk of rejection.Support function, then consider the limitationsHaemodialysisBlood passes through an external filterBloodfrom bodyExternal filterFiltered blood returnsRemoved wastesand excess waterNeeds repeated treatmentReplaces only some kidney functionsKidney transplantA donor kidney is placed in the bodyInside the bodyDonor kidneyFilters bloodBlood inBlood outUrineNeeds a donor and ongoing careRejection remains possible
Scroll diagram horizontally to read all labels.
These simplified function diagrams do not show anatomical positions or shapes. Haemodialysis is one form of dialysis; other forms also exist. Follow the labelled arrows: the blood returning to the body is separate from the removed wastes and excess water.

Compare benefits with limitations

Keep a benefit and a limitation together for each technology. “Technology helps” is too vague; “technology is perfect” ignores what happens after the procedure.

  • Dialysis removes wastes and excess water, but replaces only some functions and requires repeated treatment.
  • A transplant can restore much function with a donor kidney, but needs a donor, surgery and ongoing care, with a risk of rejection.

The NIDDK comparison of kidney-failure treatments explains the purposes and limits of these approaches.

Worked examples

Modelled example 1

Why one dialysis session is not enough

Core

Problem

A fictional case states that the kidneys have not recovered, but dialysis has removed wastes and excess water in one session. Explain why further sessions may still be needed.

Study the worked solution

  1. Connect the missing function to continued need

    Method

    Trace what happens between treatment sessions.

    Reason

    Removing the current build-up does not permanently stop waste production or restore kidney function.

    Working

    The body continues producing wastes and taking in water. The kidneys still cannot remove enough wastes and excess water, so these can build up again. Dialysis supports removal during treatment; it does not repair the kidneys. Further sessions are therefore needed while the underlying loss of function continues.

Challenge 2

Compare two forms of kidney support

Minimal support

Problem

A student says, “A kidney transplant and dialysis are both complete, one-time cures for kidney failure.” Correct the claim by explaining one benefit and one limitation of each technology.

Give a balanced comparison

Hints

Hint 1: dialysis

Does the treatment replace all kidney function permanently, or must it be repeated?

Hint 2: transplant

Could the immune system respond to tissue from another person?

View solution step by step

  1. Balance benefits and limitations

    Method

    Describe what each option can do without calling either a guaranteed cure.

    Reason

    Medical technologies can restore or support function but still have practical and biological limits.

    Working

    Dialysis removes wastes and excess water from the blood when kidneys cannot do so adequately, but it requires repeated treatment and may become a lifelong dependence. A successful kidney transplant can restore much kidney function for longer periods, but a suitable donor is needed and the recipient’s immune system may reject the organ.

Practise independently

A fictional information card calls dialysis and transplantation the same one-time cure. Compare one benefit and one limitation of each.

Need a hint?

Keep the purpose and limitation paired for each technology.

Check your answer

Dialysis removes wastes and excess water but requires repeated treatment and replaces only some functions. A transplant can restore much function but needs a donor, surgery and ongoing care, with rejection risk. Neither description justifies calling it a guaranteed one-time cure.

One-minute check

Without looking back, explain why dialysis may need to continue after one successful session. Then explain tissue rejection and give a benefit and a limitation of a kidney transplant.

Syllabus and review details

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