Gas and mass transfer | Artery

Gas and mass transfer

In the capillaries the mass transfer of the blood with the environment takes place. This is favoured by the very thin vessel wall and the huge total surface area of all capillaries. Some substances, such as gases, can pass through the vessel wall unhindered, while other substances are absorbed into the tissue via special transport mechanisms.

The permeability of the vessel wall varies greatly from organ to organ. A continuous vessel wall (endothelium) has a permeability (permeability) that varies from organ to organ. A fenestrated vascular wall (endothelium) allows mainly water molecules to pass through, whereas a discontinuous vascular wall (endothelium) is completely permeable for all components of the blood.

Arteriosclerosis is the collective term for all pathological changes in arteries. These changes can have different causes. The most common form is atherosclerosis, which in our latitudes is often equated with arteriosclerosis.

This pathological change is often found in large and medium-sized vessels and is promoted by damage to the innermost vascular layer. This damage causes the smooth surface of the artery to become roughened and components of the blood such as cholesterol, macrophages and fats can accumulate there and develop into a larger plug (atheromatous plaques). This leads to a narrowing of the vascular space (stenosis) and possibly to reduced blood flow in the tissue behind the artery.

If an artery closes as a result of a very large plug, the tissue behind it dies because it can no longer be supplied with oxygen and nutrients. This is called an infarction. These vascular changes are normal with increasing age, but can be extremely promoted by various risk factors such as smoking (nicotine abuse), high blood pressure or diabetes.


PAVK, short for Peripheral Arterial Occlusive Disease, is a disease of the arteries. It results in stenosis (narrowing) or closure of arteries, in most cases due to arteriosclerosis. The risks include diabetes mellitus (diabetes), smoking, high blood pressure and lipid metabolism disorders, i.e. too high a level of fatty acids and cholesterol in the blood.

Often the legs are affected, which then hurt due to arterial undersupply. The consequence is that one can only walk short distances, which is why PAVK was also given the nickname “window dressing”. A simple diagnosis is the examination of the skin colour (in side comparison).

If the skin on the foot is very pale and cold compared to the opposite side, there is most likely a circulatory disorder. However, there are many more specific examination methods. The symptoms can vary depending on the degree of occlusion.

In stage I, the affected persons do not notice anything of your disease. In stage II, a distinction is made between IIa, where those affected can walk continuously for more than 200 metres, and IIb, where those affected can walk continuously for less than 200 metres. In stage III pain occurs at rest.

In stage IV, necrosis (death of tissue) occurs. A distinction is also made here between IVa and IVb. In stage IVa dry necrosis occurs due to a lack of blood circulation.

The tissue turns black. In stage IVb, a bacterial infection of the necrosis occurs. The problem here is that the bacterial infection is difficult to fight, since the body’s immune system cannot transport the infection via the undersupply. The therapy of PAVK ranges from lifestyle, medication and bypass surgery to amputation of the dead tissue.