Kidney failure and Medical diagnosis

Question 1

Describe ways in which the kidneys can be damaged.

Answer 1

• Kidney infections (podocytes/ tubules may be damaged or destroyed).
• Raised blood pressure (can damage epithelial cells and basement membrane).
• Genetic conditions (e.g. polycstic kidney disease where healthy kidney is replaced fluid-fluid cysts or damaged by pressure from cysts).

Question 2

Describe how the components of urine may be affected if the kidneys are infected or are affected by high BP.

Answer 2

• Protein in the urine: if the basement membrane or podocytes of the Bowman’s capsule are damaged they no longer act as filters and large plasma proteins can pass into the filtrate and are passed out into the urine.
• Blood in the urine: another symptom of the filter process is no loner working.

Question 3

Describe 6 effects of kidney failure.

Answer 3

The concentrations of urea and minerals ions build up in the body. The effects include:

• Loss of electrolyte balance; if the kidneys fail, the body cannot excrete excess sodium, potassium, and chlorine ions. This causes osmotic imbalances in the tissues and eventual death.
• Build-up of toxic urea in the blood; if the kidney’s fail, the body cannot get rid of urea and it can poison the cells.
• High BP; the kidneys play an important in controlling BP by maintaining water balance of the blood. If the kidneys fail, the blood pressure increases and this can cause a range of health problems including heart problems and strokes.
• Weakened bones as calcium/phosphorous balance in the blood is lost.
• Pain and stiffness in joints as abnormal proteins build up in the blood.
• Anemia; the kidneys help produce a hormone called erythropoietin that stimulates the formation of RBCs causing tiredness and lethargy.

Question 4

State one measure that is used to indicate kidney disease.

Answer 4

Glomerular filtration rate (GFR) (cm3/min)

Question 5

Describe how glomerular filtration rate can be estimated and describe the precautions that need to be taken when interpreting the results.

Answer 5

• A blood test is used to measure the level of creatinine in the blood. Creatinine is a breakdown product of muscles.
• If the higher level of creatinine in the blood goes up, it is a sign that the kidneys are not working properly.
• However, must consider that GFR decreases steadily with age even if you are healthy, and men have more muscle mass than women so are likely to have more creatinine.

Question 6

State the two main ways in which kidney failure is treated.

Answer 6

• Dialysis

- Transplant

Question 7

Define the term “renal dialysis”.

Answer 7

The function of the kidneys is carried out artificially to maintain the salt and water balance of the blood.

Question 8

Define the term “haemodialysis”.

Answer 8

• The filtering of blood through a semi-permeable membrane in a dialysis machine to remove waste products.

Question 9

Define the term “peritoneal dialysis”.

Answer 9

• A type of dialysis that uses the peritoneum in a person’s abdomen as the membrane through which fluid and dissolved substances are exchanged with the blood.

Question 10

Draw, label and annotate a diagram to show the process of haemodialysis.

Answer 10

• Usually carried out in a hospital.
• Blood leaves the patients body from an artery and flows into the dialysis machine, where it flows between partially permeable dialysis membranes.
• These membranes mimic the basement membrane of the Bowman’s capsule.
• On the other side of the membrane is the dialysis fluid.
• During dialysis it is vital that patients lose the excess urea and mineral ions that built up in the blood and retain substances like glucose and some mineral ions.
• The process is entirely dependent on diffusion, there is no active transport.

Question 11

What is the counter-current exchange system in haemodialysis?

Answer 11

• The blood and dialysis fluid flow in opposite directions. This maintains a steep concentration gradient and so maximises the exchange that takes place.

Question 12

What are the implications of haemodialysis for the patient?

Answer 12

• Must remain attached to a dialysis machine several times a week for many hours.
• Must carefully control their diet, with little protein or salt.
• Monitor fluid intake carefully.

Question 13

Describe the constituents of the dialysis fluid and explain why this make up is necessary.

Answer 13

• During dialysis it is vital that patients lose the excess urea and mineral ions that built up in the blood and retain substances like glucose and some mineral ions.
• The dialysis fluid contains normal plasma levels of glucose and mineral ions so that there is no net movement of glucose. This is also means that any excess mineral ions diffuse out into the dialysis fluid down a concentration gradient.
• Dialysis fluid contains no urea so there is very steep concentration gradient from the blood to the fluid. This causes urea to diffuse out.

Question 14

Describe how molecules move across the dialysis membrane.

Answer 14

Diffusion down a concentration gradient. There is no active transport.

Question 15

Describe the process of peritoneal dialysis.

Answer 15

• The peritonuem (abdomen lining) acts as a natural dialysis membrane.
• Normally done at home and patient can carry on with their normal life.
• The dialysis fluid is introduced into the abdomen using a catheter.
• It is left for several hours so that dialysis can take place across peritoneal membrane. Urea and excess mineral ions pass out of the blood capillaries, into the tissue fluid and out across into the dialysis fluid.
• The fluid is then drained off and discarded, leaving the blood balanced again and the urea and excess mineral ions removed.

Question 16

Draw a table to compare haemodialysis with peritoneal dialysis.

Answer 16

Haemodialysis:
- interrupts daily life as many hours must be spent several times a week attached to the dialysis machine.

Peritoneal dialysis:

• Can continue with every day life
• Perhaps more invasive.

Question 17

Describe how transplantation can treat kidney failure.

Answer 17

• A healthy kidney from a donor is placed within the body.
• The blood vessels are joined and the ureter of the new kidney is inserted into bladder.
• Will function normally for many years.

Question 18

Describe the limitations of transplantation as a treatment for kidney failure.

Answer 18

• Risk of rejection; the antigens on the donor organ may differ from the antigens on the cells of the recipient and the immune system is likely to recognise this.
• Can result in destruction of new kidney.
• Transplanted kidneys do not last as long as an original kidney would (about 9-10 years).

Question 19

Draw a table to compare treating kidney failure with dialysis and treating kidney failure with transplantation.

Answer 19

Dialysis:

• readily available
• lead a relatively normal life
• monitor diet carefully
• big time commitment
• in the long-term, much more expensive than a transplant
• can eventually cause damage to the body

Transplant:
- free from the restrictions of the regular dialysis sessions and dietary monitoring
-

Question 20

How to reduce the risks of kidney transplantation?

Answer 20

• Match between antigens of donor and recipient are made as close as possible i.e. people with the same blood group.
• Use of immunosuppressant drugs for the rest of their lives. Reduces risk of rejection but makes you vulnerable to infection.

Question 21

Explain, in general, why analysis of urine can act as a good diagnostic test for different diseases.

Answer 21

• Urine contains the breakdown products of a whole number of chemicals i.e. hormones and toxins.
• If you are affected by a disease, it is likely that new substances show up in your urine.

Question 22

Name the hormone tested for in pregnancy tests and state where it is produced and when it starts being produced.

Answer 22

• The developing placenta starts producing a chemical chorionic gonadotrophin (hCG) after the humam embryo has implanted into the uterus.
• Some of this hormone is found in the blood and urine of the mother.

Question 23

Define the term “monoclonal antibody”.

Answer 23

Monoclonal antibodies -

Antibodies from a single clone of cells that are produced to target the particular cells or chemicals in the body.

Question 24

Describe how monoclonal antibodies to hCG are produced.

Answer 24

• A mouse is injected with hCG so that it makes the right antibody.
• The b-cells that make the required anitbody are then removed from the spleen of the mouse and fused with a type of cancer cell called myeloma, which divides very rapidly.
• This new fused cell is known as a hybridoma. Each hybridoma reproduces rapidly, resulting in a clone of millions of ‘living factories’ making the desired antibodies.
• These monoclonal antibodies are collected and purified in a number of ways.

Question 25

Describe the main stages in a pregnancy test.

Answer 25

• The wick is soaked in urine.
• The test contains mobile monoclonal antibodies that have very small coloured beads attached to them. They will only bind to hCG. If a women is pregnant the hCG in her urine binds to the mobile monoclonal antibodies and forms a hCG/antibody complex.
• The urine carries on along the test stick until it reaches a window.
• Here there are immobilised monoclonal antibodies arranged in a line or a pattern (e.g positive sign) that only bind to the hCG/antibody complex. If the woman is pregnant, a coloured line or pattern appears in the first window.
• The urine continues up through the test to a second window.
• Here there is a second line of immobilised monoclonal antibodies that bind to mobile antibodies whether they are bound to hCG or not. This coloured line forms regardless of whether the women is pregnant or not. It simply indicates the test is working.

Question 26

Define the term “anabolic steroid” and explain why they may give a benefit to athletes.

Answer 26

• Anabolic steroids are drugs that mimic the action of the male sex hormone testosterone and they stimulate the growth of muscles.

Question 27

Describe how urine is tested for anabolic steroids.

Answer 27

• Anabolic steroids are excreted in the urine.
• By testing the urine using gas chromatography and mass spectrometry.
• The urine sample is vaporised with a known solvent and passed along a tube.
• The lining of the tube absorbs the gasses and is analysed to give a chromatogram that can be read to show the presence of drugs.

Question 28

Describe how urine testing is used to see if someone has been taking illegal drugs.

Answer 28

• Drugs (or the breakdown products of drugs) are filtered through the kidney and stored in the bladder.
• Suspect drug-user must provide a urine sample and this will be divided into two.
• The first sample can be tested using an immunoassay (a type of chemical test), using monoclonal antibodies to bind to the drug or its breakdown product.
• If this shows positive, the second sample is run through a gas chromatography to confirm the presence of the drug.

Question 29

Explain why it may be possible to test for drug use some time after a person has taken the drug.

Answer 29

The metabolites (breakdown products) of the drug are filtered through the kidney and stored in the bladder, so they can be detected sometime after they have been taken.