Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.

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This follows on from Homeostasis, Excretion, and the Kidneys, and links with a small section on Kidney dialysis machines.

After surgery (i.e. any sort of operation - not necessarily on the kidneys), it is common for hospital staff to monitor blood pressure and urine output.
Can you explain why they do this, in relation to the normal operation of the kidney and circulatory system, as outlined in previous units?

> If blood pressure falls - no filtration (first stage in kidney processing) - so no urine output (leading to buildup of toxic substances e.g. urea)

If the kidneys stop working (renal failure), then urea and other waste products will accumulate leading eventually to death. The two main ways that this can be dealt with are by dialysis using an "artificial kidney" machine (see later), or by a kidney transplant.

Kidney transplants

These operations are nowadays quite common, and probably the most successful transplants, in terms both of healthcare economics and raising the quality of life for the people affected.

It is normal practice to place the transplanted kidney into the abdomen, and not to remove the non-functioning kidneys, unless they are infected. See diagram below.

transplanted kidney
What other link must be made between the transplanted kidney and the body to allow the kidney to work?

> blood supply - artery & vein

Suggest one advantage of transplanting the kidney in the position shown rather than in the normal position.

> space! - other (first) kidneys may recover

Since a person can function with only one kidney, it is sometimes possible for a healthy person to donate a kidney to another, so that each has one functioning kidney. Such a transplant is especially possible between members of the same family, where tissue rejection is less likely due to closeness of tissue typing.

It is also possible to use both kidneys from the body of someone who has recently died, or whose body systems have been kept functioning after death of the brain.

Why is it essential to use kidneys as quickly as possible?

> kidneys continue to respire, so they will use up oxygen and "food", then gradually deteriorate and die

Kidneys for operations are transported in special containers, packed in ice.

What does the cooling do for them?

> slows down their respiration and deterioration

Why not freeze them?

> ice crystals would damage cell structures, especially membranes


You should remember that in dialysis, some dissolved substances (solutes) are able to pass through a partially permeable membrane, but not other substances. The membrane has extremely small perforations which allow only the smaller molecules through [like a tea bag?].

In some respects this process is like the first of the processes going on in the kidney:

- (ultra) filtration. However, there is no equivalent of the second process - selective reabsorption - and it is much less efficient and quite inconvenient.

Blood is taken from a patient's arm, passed through a machine and then returned with a lower urea content. They thus have to be immobile for a few hours, several times a week.

Inside the machine, the blood is passed into a chamber lined with a membrane, on the other side of which is a liquid (dialysis fluid) which is in osmotic balance with the blood plasma. Due to differences in concentration, urea crosses the membrane (together with other wastes) and passes away in the dialysis fluid, which is run away to waste.

A complex arrangement of many interleaved layers of membrane are used, in order to increase the surface area for the exchange.

Fill in the diagram alongside to show the details of the dialysis process, using a simple key for the components of blood.

dialysis animation


What other (useful) substances are likely to cross the membrane and become lost?

> glucose, salts

How can the bad effects of such a loss be cancelled out?

> put (balanced amounts of) glucose and salts in dialysis fluid

"Specimen" Urine Samples in diagnosis of kidney disease and other conditions

Urine is an example of a biological fluid which can be fairly easily collected, and which can be used to give an indication of an individual's state of health. In particular, it may show if the individual is suffering from an abnormal condition, as well as giving clues about their lifestyle.

A urine sample is normally freshly collected at a clinic, usually in a sterile container, and either tested straight away or sent to specialist laboratory.

List some abnormal conditions - "diseases" - which may be detected from examining someone's urine sample.

> diabetes

> kidney failure/infection

List some clues about lifestyle, personal habits etc. - which may be detected from examining someone's urine sample.

> drug usage, e.g. steroids (recreational/medicinal)

(also antibiotics etc.)

> pregnancy

> alcohol consumption

> diet e.g. protein eaten

Why is it usually necessary to use a sterile container for urine samples?

> bacteria will grow if left some time

What is meant by a mid-stream urine sample?

> after "pipes flushed"(!) to reduce external contamination

Background to practical activity

The exercise below is designed to show how 2 simple and rapid tests (as used in clinics) can assist in the diagnosis of kidney problems. These rely on chemical reagents attached to plastic strips which are dipped into the specimens, and the resulting colour changes are compared with standards to give a broad indication of symptoms.

Clinistix colour comparison chart

Clinistix are used to show the presence of glucose ("blood sugar") in urine, which is a symptom of the condition known as diabetes mellitis.

Describe how the glucose gets into the urine.

> excess glucose (due to unregulated "blood sugar" levels) is not absorbed in first convoluted tubule, so it passes on into the urine

Why is it not normal for glucose to be in the urine?

> glucose level is usually within limits, and usually all glucose is reabsorbed

Albustix are similarly used to test for the plasma protein albumin in the urine, which is an indication of renal (kidney) failure.

Albustix colour comparison chart Describe how the albumin gets into the urine.

> damage to membrane of glomerulus allowing more contents of blood out

Why is it not normal for albumin to be in the urine?

> being "large" molecules, they are usually kept back by the membrane

What other ("low-tech") tests could you perform on these samples to confirm their results?

?(for glucose) >Benedict's test (result = orange ppt) ?(for protein) >Biuret test (result = purple colour)

Examine the "specimens" provided using Clinistix and Albustix and record the results in the table below.

Diagnose each patient's problems and, if you can, decide on an appropriate course of action.

Clinistix Albustix
Pre-test check Colour of "stix" before test red yellowy-green
Clinistix Albustix
Patient's name Colour of "stix" after test red yellowy-green
Norman Leadswinger Your diagnosis
i.e. interpretation of this result
Nothing abnormal
Treatment suggested
to remedy condition
Go home!
Clinistix Albustix
Patient's name Colour of "stix" after test dark purple yellowy-green
Dexter T. Rose Your diagnosis
i.e. interpretation of this result
Glucose in urine - symptom of Diabetes mellitus
Treatment suggested
to remedy condition
Modify diet - low sugar/Course of insulin injections
Clinistix Albustix
Patient's name Colour of "stix" after test red blue-green
Albert Minn Your diagnosis
i.e. interpretation of this result
Albumin in urine - possible kidney failure
Treatment suggested
to remedy condition
Arrange dialysis/put on kidney transplant list

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