Functions of capillaries

The function of the capillaries is mainly mass transfer. Depending on where the capillary network is located, nutrients, oxygen and metabolic end products are exchanged between the bloodstream and the tissue. Nutrients are supplied to the tissue, waste products are absorbed and carried away.

Depending on the oxygen requirement of a particular tissue and the metabolic activity to be found there, this tissue is more or less densely covered with capillaries. Oxygen- and nutrient-rich blood reaches the tissue via the capillaries. This blood is then released into the tissue via the thin capillary wall from the inside of the blood vessel.

The tissue constantly needs new nutrients and oxygen. Metabolically active tissues include, for example, the brain, skeletal muscles and the heart, which is why they are permeated by many capillaries. Tissues that are less metabolically active, on the other hand, have few or even no capillaries.

These include mainly cartilage tissue, the lens of the eye and the cornea. At the same time, the blood in the capillaries absorbs waste products of the tissue and carbon dioxide and transports them to the lungs. In the lung, carbon dioxide is released from the blood and oxygen is absorbed by the lungs.

The released carbon dioxide is breathed out through the lungs and the absorbed oxygen is transported into the tissue. The difference in the concentration of a molecule between the blood vessels and the tissue is important for mass transfer. The gas or mass transfer always takes place where there is less of the corresponding substance.

Because a capillary network consists of a large number of capillaries, a very large area is available for mass transfer. In addition, the blood flows more slowly in the capillaries, so that there is enough time for mass transfer. Together with the thin wall structure, the optimal conditions for the most effective mass transfer are given.

This could also be interesting for you: Vascular supply of the lungThe mass exchange is the main task of capillaries. Depending on the tissue, different substances can be exchanged. The decisive factor for mass transfer is the difference in concentration of the respective substance.

A substance will always migrate into the tissue where less of it is present. For example, oxygen is exchanged from oxygen-rich blood into the tissue where oxygen is needed. This also applies to nutrients.

In contrast, the carbon dioxide or waste products produced in the tissue are released from the tissue into the blood and transported away from there. This gas exchange is reversed in the lungs. In the lungs, oxygen is absorbed and carbon dioxide is breathed out.

The capillaries of the lung absorb oxygen corresponding to the difference in concentration and the carbon dioxide released by the tissue passes through the capillary wall towards the lung. Other important factors for the exchange of substances are the blood pressure in the capillaries and the hydrostatic pressure.Due to the pressure differences that this creates between the inflowing part of the capillary and tissue, liquid and small molecules are transported into the tissue. In the outflowing part of the capillary, the so-called colloid-osmotic pressure created by the proteins in the blood plays a decisive role. This pressure causes a slight reabsorption of liquid into the blood. This is important for regulating the fluid exchange.