為何洗腎的人會感到疲累?

洗腎（血液透析）其實係將血液泵出黎，經過diffusion，然後注入返去身體裡面，攰嘅原因之一係因為血液離開身體，會損失咗部份熱力（雖然洗腎機內會為血液保溫），即係人體需要產生多D嘅熱能，咁就會消耗一D體力，其二係血液循環增加，心臟需要嘅動力多咗，肺部需要嘅動力亦多咗（道理同浸完溫泉一樣）．
血液透析係將血液泵出，利用diffusion，透過一塊半透膜，將血裡面嘅廢物滲透到膜嘅另一邊，所以係用diffusion原理，而唔會用active transport嘅．
不過如果係腹膜透析，咁就係用osmosis嘅原理．
詳情睇下以下資料：
Principle
Dialysis works on the principle of the diffusion of solutes across a semipermeable membrane. Blood flows by one side of a semipermeable membrane, and a dialysis solution or fluid flows by the opposite side. Smaller solutes pass through the membrane. The concentrations of undesired solutes (for example potassium, urea, and phosphorus) are high in the blood, but low or absent in the dialysis solution and constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this side of the membrane. The dialysis solution has levels of minerals like sodium and chloride that are similar to their natural concentration in healthy blood. For another solute, bicarbonate, dialysis solution level is set at a slightly higher level than in normal blood, to encourage diffusion of bicarbonate into the blood, to neutralise the acidosis that is often present in these patients.
Hemodialysis
In hemodialysis, the patient's blood is pumped through the blood compartment of a dialyzer, exposing it to a semipermeable membrane. Dialysis solution is pumped through the dialysate compartment of the dialyzer, which is configured so that the blood and dialysis solutions flow on opposite sides of the semipermeable membrane. The cleansed blood is then returned via the circuit back to the body. Ultrafiltration occurs by increasing the hydrostatic pressure across the dialyzer membrane. This usually is done by applying a negative pressure to the dialysate compartment of the dialyzer. This pressure gradient causes water and dissolved solutes to move from blood to dialysate, and allows removal of several liters of excess salt and water during a typical 3-4 hour treatment. Dialysis patient weight is measured in kilos: therefore, one kilo of fluid equals 2.2 pounds of body weight. Hemodialysis treatments are typically given three times per week, but more frequent sessions, which are usually 2-3 hours in duration given 5-6 times per week can be sometimes prescribed. Hemodialysis treatments can be given either in outpatient dialysis centers or can be done by a patient at home, providing they have suitable help and accommodation.
Peritoneal dialysis
In peritoneal dialysis, a sterile solution containing minerals and glucose is run through a tube into the peritoneal cavity, the abdominal body cavity around the intestine, where the peritoneal membrane acts as a semipermeable membrane. The dialysate is left there for a period of time to absorb waste products, and then it is drained out through the tube and discarded. This cycle or "exchange" is normally repeated 4-5 times during the day, (sometimes more often overnight with an automated system). Ultrafiltration occurs via osmosis; the dialysis solution used contains a high concentration of glucose, and the resulting osmotic pressure causes fluid to move from the blood into the dialysate. As a result, more fluid is drained than was instilled. Peritoneal dialysis is less efficient than hemodialysis, but because it is carried out for a longer period of time the net effect in terms of removal of waste products and of salt and water are similar to hemodialysis. Peritoneal dialysis is carried out at home by the patient and it requires a substantial degree of motivation and support to perform. It does free patients from the routine of having to go to a dialysis clinic on a fixed schedule multiple times per week, and it can be done while traveling with a minimum of specialized equipment.