Unit 12- Excretion

04.28.2020
09:10:48
Biology/ grade 9-Today’s topic-kidney dialysis-course book- pages 158 and 159.

Main points-
The kidneys might not work properly for several reasons, including accidents or disease
Humans can survive with one functioning kidney, but if both are damaged then there will quickly be a build-up of toxic wastes in the body which will be fatal if not removed.

The usual treatment for someone with kidney failure is dialysis.
This is an artificial method of filtering the blood to remove toxins and excess substances.
Patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and restore/maintain the water and salt balance of the blood.
Unfiltered blood is taken from an artery in the arm, pumped into the dialysis machine and then returned to a vein in the arm.
Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane  – the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists.

Dialysis fluid contains:
a glucose concentration similar to a normal level in blood
a concentration of salts similar to a normal level in blood
no urea

How a dialysis machine works to filter the blood:

As the dialysis fluid has no urea in it, there is a large concentration gradient – meaning that urea diffuses across the partially permeable membrane, from the blood to the dialysis fluid.
As the dialysis fluid contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists.
As the dialysis fluid contains a salt concentration similar to the ideal blood concentration, movement of salts across the membrane only occurs where there is an imbalance (if the blood is too low in salts, they will diffuse into the blood; if the blood is too high in salts, they will diffuse out of the blood).
The fluid in the machine is continually refreshed so that concentration gradients are maintained between the dialysis fluids and the blood.
Dialysis may take 3-4 hours to complete and needs to be done several times a week to prevent damage to the body from the buildup of toxic substances in the blood.
An anticoagulant is added to blood before it runs through the machine to prevent the blood from clotting and slowing the flow.

No homework.