molecular movement in the solutions (Diffusion)

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CONVECTION :

This type of movement is characterized by the drive of the molecules under the influence of a hydrostatic pressure gradient or the thrust by neighboring molecules (who, in dilute solutions are substantially solvent molecules).

TRANSFER THE CONVECTIVE :

Due to an external force to the molecule associated with the hydrostatic pressure.

Can be deduced from the definition of molar mechanical mobility b that the convective flow:

Jc = -bSpore.grP

the sign (-) convective transfer of makes the place strong pressure at the low pressure.

For the solvent: the volume of water flow is convective:

Qc= -bH20 . VH20 . Spore . city ​​P

NOTE INFLUENCE THE SIZE OF THE MOLECULE :

Unlike diffusive transfer, convective transfer is not influenced by the size of the molecule, it is related to the training of the solute molecule (even large molecule) by neighboring solvent molecules.

A large molecule has a lower mobility, but it is driven by a member molecules.

SOLVENT-DRAG :

As the solvent molecules outnumber those of solute, they are capable of movement in a mass of lead with them dispersed solute molecules. The convective heat transfer is called solute : solvent-drag

FILTRATION :

Diffusion through a membrane under the effect of a pressure difference.
This migration is limited by pore size – On a molecular scale sieving : ultrafiltration.

Poiseuille law :

MEDICAL APPLICATIONS :

dialysis :

  • problematic
  • Peritoneal dialysis
  • Hemodialysis and artificial kidney

Filtration :

  • Hémofiltration

DIALYSIS :

clean normal (functions) kidney patient (problems)
Regulates sodium level and amount of’water. Causes extra fluid.
Eliminates waste. N’not eliminate waste such as :

  • L’urea
  • creatinine
  • potassium
Produces hormones. Adjusts the production of’controlling hormones:

  • Blood pressure
  • The red blood cell production
  • L’calcium absorption

TREATMENT :

  • The treatment is a kidney transplant (artificial or real) placed a little above the bladder.
  • Meanwhile the transplant peritoneal dialysis is performed.

MEMBRANE DIALYSANTE :

Passes free water and small molecules dissolved therein but stops macromolecular (molecular mass of molecules greater than or equal to 10000 g / mol) Example: The capillary wall as represented by the artificial kidney.

KIDNEY DIALYSIS AND ARTIFICIAL :

  • Dialysis is a machine whose function is to replace the work of the kidney. It thus allows’purify a large amount of blood (on average 70 L per session’hemodialysis) toxic waste and’excess water retained. Although’indispensable, she n’is not without constraints : it binds to life to dialysis sessions, it mobilizes the patient for several hours,
  • There are two dialysis techniques

1- HEMODIALYSIS :

  • the oldest method, the patient is connected to a large machine called the dialyzer or more simply a « artificial kidney ». A l’interior, the blood is cleared of waste and, once purified, it is reintroduced into the circulatory system.
  • two pipes, one for the blood that comes out,
  • one for the blood that enters, connect the arm of the patient to the machine.

PERITONEAL DIALYSIS (DP) :

Extrarenal technique using the peritoneum as a membrane’exchange between waste-laden blood and a sterile liquid repeatedly introduced into the’abdomen. This technique is daily, require multiple exchanges during the day according to a technique known by sachets (CAPD).

  1. Introducing the dialysate into the peritoneal cavity
  2. The waste is transferred : Sang -» dialysat
  3. Recovery dialysate

DISADVANTAGE :

Little selectivity for the molecular weight

  • Protein Beads compensate
  • Infection Risks

2- HÉMOFILTRATION :

It is a technique of dialysis for 24 hours / 24 and several days if necessary, existing since the early 1990 in ICU for patients requiring renal replacement and whose blood pressure is fragile.

HÉMOFILTRATION

It makes it possible to "cleanse" the blood of deleterious substances and to remove the’excess water from cells.

On l’often use in case of septic shock, d’acute edema of the lung (water overload).

DIFFERENCE BETWEEN HEMODIALYSIS AND hemofiltration :

hemodialysis HD Hémofiltration HFC
  • Diffusion
  • Using the concentration gradient between plasma and dialysate.
  • L’transport intensity essentially depends on the concentration gradient and the diffusion coefficient of the substance considered
  • Eliminates molecules of low molecular weight and present in large numbers as tured, potassium or creatinine.
  • convection
  • using the hydrostatic pressure gradient arteriovenous
  • pressure gradient dependent and the size of the membrane pores and the viscosity
  • Eliminates the molecules whose molecular weight is higher but whose size remains smaller than the pores of the membrane, such myoglobin, and who are in low numbers in the solute

Theoretically, the two techniques are therefore complementary and the choice of’one or more’other should depend on the nature of the substances that l’we want to eliminate.

Course of Dr Allouache – Faculty of Constantine

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