chapter 15 p6 Flashcards
Urine and anabolic steroids:
Athletes and body builders may try to cheat by using anabolic steroids.
Anabolic steroids are drugs that mimic the action of the male sex hormone testosterone and they stimulate the growth of muscles.
They are, however, excreted in the urine.
By testing the urine using gas chromatography and mass spectrometry, scientists can show that an individual has been using these drugs, which are banned in all sports.
The urine sample is vaporised with a known solvent and passed along a tube.
The lining of the tube absorbs the gases and is analysed to give a chromatogram that can be read to show the presence of the drugs.
Urine and drug testing:
Urine is tested for the presence of many different drugs, including alcohol.
Because drugs or metabolites - the breakdown products of drugs - are filtered through the kidneys and stored in the bladder, it is possible to find drug traces in the urine some time after a drug has been used.
If someone is suspected of having taken an illegal drug.
they may be asked to provide a urine sample and this will be divided into two.
The first sample may be tested by an immunoassay, using monoclonal antibodies to bind to the drug or its breakdown product.
If this shows positive, the second sample may be run through a gas chromatograph/ mass spectrometer to confirm the presence of the drug.
A wide range of drugs can be detected in the urine in this way
Causes and effects of kidney failure:
There are a number of reasons why the kidneys may fail.
They include
- kidney infections, where the structure of the podocytes and the tubules themselves may be damaged or destroyed;
- raised blood pressure that can damage the structure of the epithelial cells and basement membrane of the Bowman’s capsule;
- and genetic conditions such as polycystic kidney disease where the healthy kidney tissue is replaced by fluid-filled cysts or damaged by pressure from cysts.
If the kidneys are infected or affected by high blood pressure this may cause:
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 in the urine.
Blood in the urine - another symptom that the filtering process is no longer working.
If the kidneys fail completely, the concentrations of urea and mineral ions build up in the body. The effects include: p1
- Loss of electrolyte balance - if the kidneys fail, the body cannot excrete excess sodium, potassium, and chloride ions. This causes osmotic imbalances in the tissues and eventual death.
- Build-up of toxic urea in the blood - if the kidneys fail, the body cannot get rid of urea and it can poison the cells.
- High blood pressure - the kidneys play an important role in controlling the blood pressure by maintaining the 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.
If the kidneys fail completely, the concentrations of urea and mineral ions build up in the body. The effects include: p2
- Weakened bones as the calcium/phosphorus balance in the blood is lost.
- Pain and stiffness in joints as abnormal proteins build up in the blood.
- Anaemia - the kidneys are involved in the production of a hormone called erythropoietin that stimulates the formation of red blood cells. When the kidneys fail it can reduce the production of red blood cells causing tiredness and lethargy.
Measuring glomerular filtration rate:
- Kidney problems almost always affect the rate at which blood is filtered in the Bowman’s capsules of the nephrons.
- The glomerular filtration rate (GFR) is widely used as a measure to indicate kidney disease.
- The rate of filtration is not measured directly - a simple blood test measures the level of creatinine in the blood.
- Creatinine is a breakdown product of muscles and it is used to give an estimated glomerular filtration rate (eGFR).
- The units are cm3/min.
- If the levels of creatinine in the blood go up, it is a signal that the kidneys are not working properly.
- Certain factors need to be taken into account in the calculations to work out GFR.
- For example, GFR decreases steadily with age even if you are healthy, and men usually have more muscle mass and therefore more creatinine than women.
average GFRs in adults
Treating kidney failure with dialysis:
As you can see in Table 1, normal GFRs do not fall below 70 even in very elderly people.
A GFR of below 60 for more than three months is taken to indicate moderate to severe chronic kidney disease - and if it falls below 15, that is kidney failure.
The kidneys are filtering so little blood they are virtually ineffective.
There are two main ways in which kidney failure is treated.
In renal dialysis, the function of the kidneys is carried out artificially.
In a transplant, a new healthy kidney is put into the body to replace the functions of the failed kidneys - an animal can function perfectly well with just one healthy kidney.
There are two main types of dialysis - haemodialysis and peritoneal dialysis.
Haemodialysis:
p1
This involves the use of a dialysis machine.
It is usually carried out in hospital although sometimes patients will have a machine in their own home.
Blood leaves the patient’s 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 membranes is the dialysis fluid.
During dialysis it is vital that patients lose the excess urea and mineral ions that have built up in the blood.
Haemodialysis:
p2
It is equally important that they do not lose useful substances such as glucose and some mineral ions.
The loss of these substances is prevented by careful control of the dialysis fluid.
It contains normal plasma levels of glucose to ensure there is no net movement of glucose out of the blood.
The dialysis fluid also contains normal plasma levels of mineral ions, so any excess mineral ions in the blood move out by diffusion down a concentration gradient into the dialysis fluid, thus restoring the correct electrolyte balance of the blood.
The dialysis fluid contains no urea meaning there is a very steep concentration gradient from the blood to the fluid, and as a result, much of the urea leaves the blood.
The blood and the dialysis fluid flow in opposite directions to maintain a countercurrent exchange system and maximise the exchange that takes place.
Haemodialysis:
p3
The whole process of dialysis depends on diffusion down concentration gradients - there is no active transport.
Dialysis takes about eight hours and has to be repeated regularly.
Patients with kidney failure who rely on haemodialysis have to remain attached to a dialysis machine several times a week for many hours.
They also need to manage their diets carefully, eating relatively little protein and salt and monitoring their fluid intake to keep their blood chemistry as stable as possible.
The only time they can eat and drink what they like is at the beginning of the dialysis process.
dialysis machine diagram
Peritoneal dialysis:
- Peritoneal dialysis is done inside the body - it makes use of the natural dialysis membranes formed by the lining of the abdomen, that is, the peritoneum.
- It is usually done at home and the patient can carry on with their normal life while it takes place.
- The dialysis fluid is introduced into the abdomen using a catheter.
- It is left for several hours for dialysis to take place across the peritoneal membranes, so that urea and excess mineral ions pass out of the blood capillaries, into the tissue fluid, and out across the peritoneal membrane into the dialysis fluid.
- The fluid is then drained off and discarded, leaving the blood balanced again and the urea and excess minerals removed.
Peritoneal dialysis: diagram
donor kidney diagram
