The sum total filtrate amount in the body is almost insignificant relative to diffusion. [2]
1.4.3 Osmosis
If a semipermeable membrane separates two solutions of differing concentration, then the solvent will drift in the direction of higher concentration. The membrane is impermeable to the higher solvent concentration. This drift can be prevented by means of pressure on the more highly concentrated solution. The amount of pressure needed to bring the osmotic drift to a stop is known as the effective osmotic pressure. Osmosis is the water attraction of salts and sugars, oncosis the water uptake power of proteins. The current term for the latter is now colloid osmosis. The cause of this phenomenon lies in the activity of the solvent, which is reduced by dissolving a substance in a solvent. It is necessary that the membrane be permeable for the solvent but not the solute.
Osmotic pressure
N = number of particles, R = the gas constant, T = temperature, V = volume
Ionization of individual electrolytes also influences the number of actually available osmotically effective particles. The term “tonicity” serves to indicate the effective osmotic pressure of a solution relative to the plasma. If the pressures are equal, it is termed isotonic; hypertonic refers to a higher and hypotonic to a lower pressure.
All of these transport processes are passive; the particles involved move “downhill”. However, in many situations it is necessary to move “uphill” toward a region of higher concentration, or against osmotic pressure or an electrical gradient. This is known as active transport, and requires energy from cellular metabolism.
1.4.4 Homeostasis
The interstitial part of the extracellular fluid is the environment of body cells. Normal functioning of the cells is dependent on the constancy of this fluid. There are numerous physiological regulatory mechanisms whose purpose is to restore normal conditions after a disturbance. Most of these mechanisms work on the feedback principle. Numerous sensors located all over the body register deviations from the norm and trigger compensation mechanisms in order to return the system to normal. [1, 9]
Summarizing, one can say - simplifying somewhat - that the following forces are active in transporting materials out of the blood: the blood pressure in the capillaries and the oncotic suction of the tissue proteins exert the filtering force; the tissue pressure and the oncotic suction of blood proteins exert the resorptive force. In the current literature, oncotic suction is designated as colloidal osmotic pressure. Under physiological conditions, this generates an equilibrium in the region of the terminal vessels, i. e. the perfusion forces in the capillaries are the same in both directions. This was ascertained around the turn of the century by the physiologist Starling.
However, one should always keep in mind that, due to the complexity of the feedback mechanisms, the alteration of one factor can change numerous other substances and conditions on a continuous basis, and that the various bodily regions will each react differently. If the filter forces outweigh the resorptive forces, then a portion of the filtrate will not be returned to the capillaries, but will instead remain in the tissues.
From there it can be taken up by the lymphatic system, which can carry it on. For Manual Lymph Drainage to succeed, it is necessary to know (among other things) whether and to what degree resorption at the venous limb of the blood capillaries can be strengthened.
In this context, the following factors are influential: the blood pressure exerts a force on the vessel walls from within and.thus keeps the vessel filled out. In this manner, fluid is forced - i. e. filtered - through the permeable vessel walls. The plasma's protein components bind water and thereby also fill the vessel. However, this water attraction also works through the capillaries and thus draws water out of the tissues. Thus, besides filtration, resorption takes place at the same time. But since the other side of the capillary walls, the connective tissue, also contains protein substances, additional water molecules are induced to migrate out of the capillaries. This is yet another filtration factor. The more proteins and water in the tissues, the greater the pressure exerted on the vessels. This tissue pressure acts as a compensatory force on the capillaries and thus induces resorption. The pressure of any manual massage works with this tissue pressure, which compresses and re-sorbs.
The most important prerequisite for filtration and resorption is flow in the vessels. If a vessel is pinched shut by external pressure, then the flow stops. The region around the vessel then suffers from a lack of nutrients, and waste products pile up. If the external pressure lets up, the capillary opens up again and blood flow resumes, with elevated pressure at first - which results in increased filtration. Since the blood pressure would also have risen in the venous part, resorption is reduced. The filtering arterial power limb of the capillaries becomes longer, the resorbing venous limb of the capillaries shorter. The correct -i.e. the ideal - massage pressure for Manual Lymph Drainage works together with the tissue pressure and thus has a resorbing effect. Increasing the massage pressure thus sets clear limits to the effect(iveness) of the massage. The best resorption results are obtained by that pressure which does not quite cause compression (of the vessels).
Fig. 4: Starling's equilibrium
The construction of the vessel walls, their permeability, as well as the size relationship of the respective arterial and venous capillary limbs -all of these also influence the relationship between resorption and filtration.
Current scientific terminology refers to effective filtration pressure, which consists of the blood pressure in the capillaries minus the tissue pressure, and effective colloidal osmotic pressure consisting of the colloidal osmotic pressure in the blood minus that in the tissues. If the effective filtration pressure exceeds the effective colloidal osmotic pressure, then this leads to build-up of fluid in the tissues, the net ultra-filtrate is elevated, leading to what is termed an elevated lymph-time-volume. The lymph-obligatory load is increased.
But in addition to filtration, diffusion and osmosis, there is the factor of active transport or proteins and other substances. Only the smaller proteins (albumin) can seep through the large pores of the capillaries and thus end up in the tissues.
Active transport takes place via the vascular endothelial cells. The membrane of the endothelial cell everts itself into the vessel's lumen and takes up the protein molecule: it is enclosed in a vesicle. This vesicle drifts through the cell and releases the protein on the far side. In this manner, the protein moves from blood to tissue. This process is called cytopempsis. When other substances are transported through cells in this manner, it is termed pinocytosis. However, since there is always a drive toward homeostasis, protein is able to be transported back into the blood and the lymph by this route as well. In this form of cytopempsis, the molecular structure of the protein is not altered. This is a physiological process, an active performance on the part of the endothelial cell.
See Fig. 5.
But proteins can also enter the inner part of the cell and permeate through the plasma, whereby their molecular structure is altered by being changed into water-insoluble mucopolysaccharides and excreted onto the basement membrane. They can be stored there, or passed on to the connective tissue, after undergoing yet another structural alteration.
The endothelial cells have a special sensitivity to the body's own substances with high blood level, but also to foreign substances. In physiological permeation, protein binds with