Transport Principles - Definitions

Question 1

Diffusion

Answer 1

The movement of solutes (dissolved particles) across a semi-permeable membrane from regions of high solute concentration to regions of low solute concentration. The net transport continues until equilibrium is reached and solute concentration is the same everywhere.

Question 2

Ultrafiltration

Answer 2

Occurs when fluid moves across a semipermeable membrane as a result of a pressure gradient being applied across the membrane. The fluid will move from an area of higher pressure to an area of lower pressure.

Question 3

Osmosis

Answer 3

The movement of water from an area of low solute concentration to an area of high solute concentration, or alternatively fro an area of high water concentration to an area of low water concentration. This process occurs across a semi-permeable membrane.

Question 4

Convection

Answer 4

The process of solute drag or solute movement of middle molecules with a solvent (plasma water) from the blood compartment to that of the dialysate compartment. When a solution is moving, the solutes dissolved in it will move along with it.

Question 5

Reverse Osmosis

Answer 5

It is the opposite to osmosis. The process used in preparing source water for dialysate. In this process water is forced across a semipermeable membrane under pressure, leaving behind 95% of ionic and nonionic contaminants. This causes water to move from high concentration to low concentration of solutes.

Question 6

Sieving Coefficient

Answer 6

The measurement of the porosity of a dialysis membrane for a given solute.

Question 7

TMP

Answer 7

Transmembrane Pressue. It is the pressure gradient across the dialyser membrane. It is created by the difference between the positive pressure in the blood compartment of the dialyser and the negative pressure in the dialysate compartment of the dialyser.

Heamodialysis machines calculate this pressure automatically and it is this pressure that is the driving force for fluid removal (ultrafiltration). The heamodialysis machine will automatically adjust the TMP as venous pressure, blood flow rate and the amount of fluid to be removed changes.

Question 8

High Flux or High Permeability

Answer 8

Will allow molecules of a molecular weight less than 50, 000 daltons to pass across the membrane. They are also highly permeable for water.

Question 9

Low Flus or Low Permeability

Answer 9

Less permeable that high flux. It will only allow molecules that weigh up to 10, 000 daltons to pass across its membrane.