from Wikipedia, the free encyclopedia

A capillary (previously also known as a hair tube ) is a very fine, elongated cavity. The word is derived from the Latin word capillus (hair).


In general, capillaries are tubes with very small internal diameters. The physical effect of capillary action occurs in capillaries due to surface effects, which come to the fore in comparison to larger tubes : Liquids with high surface tension rise in capillaries, they condense on the capillary walls above their boiling point and chemical reactions can occur come that would not expire outside of capillaries. The capillarity causes z. B. Ice Lenses .

Biology / medicine

Capillaries are the smallest blood vessels . They are about 0.5 mm long and 5 to 10 µm in diameter. They form a fine network in the organs and tissues of the body and enable the exchange of substances between blood and tissue. The diameter of the pulmonary capillaries is just large enough for red blood cells to fit through one behind the other.

Biology / plants

Trachea and tracheids , only tracheids in the case of coniferous wood, form the water management system of trees and other plants. They conduct the soil water with the dissolved nutrient salts with the help of capillarity and the perspiration suction to the leaf organs of the plants.

Arable land / agriculture

In arable land, the size and distribution of the cavities ( pores ) for the water and air balance is of decisive importance for the fertility of a site. The small or smallest pores are called capillaries - thanks to the adsorption forces , the rainwater remains in them for the longest as retained water - in them moisture rises from the groundwater ( capillary rise ).


In chemical laboratories, the term capillary usually refers to the boiling capillaries . They are used for distillations both under vacuum and under normal pressure in order to avoid delayed boiling . These are very thin, flexible capillaries. They are immersed in the liquid to be distilled and should touch the bottom of the flask. Small bubbles of inert gas or air continuously enter the liquid through the capillaries , which maintain an even boiling process and thus prevent a boiling delay.

2 glass capillaries - 50 µl and 100 µl filling volume with ring mark


In analysis, with certain methods such as thin layer chromatography , glass capillaries, also called capillary pipettes, are used to measure and apply the smallest of samples. The sample is taken up either with the help of a pipette helper or mostly independently by capillary action. Capillary pipettes are usually adjusted to "In" (pouring volume).

Inkjet printer

In inkjet printers, capillaries are used to transport the ink to the print head. The advantages are enormous: The devices can be built more compact (less high), as the ink tanks are not moved with the head, as both are connected by capillaries. The print heads can be positioned finer or faster because of the lower moving mass, there is less inertia - which leads to noticeable quality improvements, especially with high-speed printing (draft printing). Amazingly, capillaries were first used by refill providers (especially for Epson printers) in order to be able to offer larger ink tanks than those offered by the printer manufacturer. These ink tanks must be installed outside the device and connected to the print head through the capillaries.

Textile industry

In the textile industry, the term capillary stands for the finest (individual) fibers that are then spun into a yarn .

The capillary thread is the single filament thread emerging from the bore of the spinning nozzle during the jet spinning process.

Other uses


  • H. Schubert: Capillarity in porous solid systems. Springer-Verlag, Berlin 1982, ISBN 3-540-11835-7