because if the concentrations are different ,important or much needed substances may pass out of the blood into the tube if the concentration of that substance is low in the patients blood, so conditions of the patient can become even worst.
Because if the dialysis fluid didn't contain glucose, the glucose in the blood will be transferred across the concentration gradient to the fluid and this will cause hypoglycemia which is dangerous.
Keep the concentration of these substances in the dialysis fluid same as in the blood, and they won't diffuse out.
As the dialysis fluid has no urea in it, there is a large concentration gradient - meaning that urea moves across the partially permeable membrane, from the blood to the dialysis fluid, by diffusion. This is very important as it is essential that urea is removed from the patients' blood.
the concentration of urea should be kept low in the dialysis fluid because urea is harmful for our body if it is not removed.
It has to flow in opposite directions to keep a balanced concentration therefore a balanced diffusion. If it went in the same direction as the blood there would be less diffusion as, for instance, by the time the dialysis fluid from the right side got the the left, no more diffusion could take place with the blood above it as the fluid would already have gone though diffusion with blood further back down the right end so particles would not move from a high concentration to a low concentration as the fluid below would have a high concentration too from what it gained back at the right end.
I guess you are asking about dialysis. dialysis is the procedure whereby the kidneys of an animal remove waste material and excess fluid from their blood. If the kidneys fail, a machine can be used to do the procedure.
dialysis
There are two methods of dialysis in use: hemodialysis (blood dialysis) and peritoneal dialysis (dialysis in the abdominal cavity). In hemodialysis, the dialysis membrane is made up of cellophane or other synthetic material that assists in the removal of impurities from the blood by their passage through these semipermeable membranes in a fluid bath. In peritoneal dialysis, the surface area of the peritoneum acts as the membrane. Dialysis fluid is introduced into the peritoneal cavity and then periodically removed along with the waste products. This procedure may be done at intervals throughout the day or during the night.
The dialysis fluid is different to plasmas in that it does not have the uric acid and urea in it.. besides that- it has no excess salts either.
diffusion
The amount of fluid removed is decreased
dialysis works just like our kidneys. if for some reason our kidneys fail to filter our blood, then dialysis is done. in dialysis our blood is filtered to remove waste products. dialysis can be done in two ways haemodialysis---it makes use of a kidney machine or artificial kidney containig a fluid with adjusted compostion. during this process the blood i pumped from the body through a tube into the fluid through a semi permeable membrane present in the fluid. this way by passing through the semi permeable membrane the nitrognenous wastes and excess salts are diffused out from the blood into the fluid. then the blood is returned into the body. this proces takes 6 to 10 hours and is to be done three times a week peritoneal dialysis----it requires abdominal incision . a cathetar is inserted through this incision inot the peritoneal cavity. a fluid bag is attached to the cathetar from the outside. in this way the fluid enters the peritoneal cavity of our body and purifies our blood. after sometime the fluid is tkane out of the peritoneal cavity back into the bag. this process takes an hour and is reapeated day or overnight the major difference between the two dialysis processes is that in the first process the blood is taken out of our body and then filtered.it is a long and lengthy process and very painful while in the second process the fluid itself is inserted into our our body and then blood is purified. this is a realtively quicker way
Urea and salts, i think so such as sodium ions