Answer about haemodialysis. Why is heparin added to the blood before it enters the unit? …
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer about haemodialysis.
- Why is heparin added to the blood before it enters the unit?
- Why does the dialysing fluid have the same composition as plasma, except for the nitrogenous wastes?
- What makes urea leave the blood?
- Why is anti-heparin added before the blood goes back to the body?
Need a reminder? The key ideaShow
Uraemia is urea in the blood. In haemodialysis, blood from an artery gets heparin. It runs through a coiled cellophane tube in a dialysing fluid that is like plasma without the nitrogenous wastes. It returns through a vein after anti-heparin. Wastes diffuse down their concentration gradient. In a model, the urea left is per cent, where the ratio is the volume of blood cleared divided by the body water. Renal calculi are stones of crystallised salts. Glomerulonephritis is the inflammation of the glomeruli.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Heparin is an anticoagulant. It stops the blood from clotting in the tubes and the unit.
Step 2. (b) The useful substances, such as glucose and salts, are at the same concentration on both sides, so they do not leave the blood. Only the wastes, which are absent from the fluid, diffuse out.
Step 3. (c) The concentration gradient. The urea is more concentrated in the blood than in the fluid, so it diffuses through the porous cellophane membrane.
Step 4. (d) Anti-heparin cancels the heparin, so that the blood of the patient can clot normally.
Answer: (a) to stop clotting; (b) to keep the useful substances and remove only the wastes; (c) the concentration gradient; (d) to cancel the heparin.
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