Microcirculation

describes the blood movement in the capillaries. Determining factors: the functional organization of this area (haemodynamics), flow properties, changes in the clearing width, the arteriolovenous pressure gradient as the driving force, the transmural (through an organ wall) pressure as well as permeability and mass transfer mechanisms.

Perfusion is actively modified by the smooth muscles of the small arteries (arterioles, which in turn are influenced by local metabolic, nervous and hormonal mechanisms as well as ions) in terms of adapting the driving pressure gradient and transmural pressure to local needs. Here also a part of the blood plasma water (possibly also parts of the plasma proteins) escapes through the capillary endothelia into the interstitium, in order to leave it again, after perfusion or diffusion, at the venous part of the capillaries and through lymph capillaries.

The movement of the erythrocytes takes place passively under the influence of the plasma flow and under elastic deformation (armor chain rotation of the membrane); the less flexible nucleus-containing blood cells (lympho- and leukocytes), on the other hand, can cause the local blood flow to be reduced. Slow down blood flow; carried thrombocytes - if not clumping - do not cause any significant flow obstruction. Functional acceleration of microcirculation manifests itself in hyperemia (increased blood volume). Disturbances of microcirculation result from a marked reduction in blood pressure (e.g. in shock), narrowing and displacement of the small arteries and capillaries (e.g. arterial occlusive disease, microembolia, venous backwater (thrombosis), increased blood viscosity.

https://de.wikipedia.org/wiki/Mikrozirkulation _{(Wikipedia CC-by-sa-3.0)}