Blood flow

As Blood flow the movement of the blood in the body's circulation is understood. The blood flow is influenced by various conditions in the body.

What is the blood flow?

Blood is a body fluid made up of special blood cells and liquid blood plasma. The blood is distributed in the body via the bloodstream. The blood circulation begins in the heart. Various blood vessels such as arteries, arterioles and capillaries distribute the oxygen-rich blood in the body. Venules and veins transport the deoxygenated blood back to the heart.

The movement of blood in the blood vessels is called blood flow. Various factors affect blood flow. It depends, for example, on blood pressure, the viscosity of the blood and the resistance of the blood vessels.

In principle, however, the blood flow follows the laws of hemodynamics. Hemodynamics deals with the flow techniques of the blood. The blood flow affects the functionality of the body.

Tissues that receive too little oxygen due to disturbed blood flow can no longer function properly. This is how various diseases can develop. Serious illnesses, such as heart attack or stroke, are also based on a disruption of the blood flow.

Function & task

The hemodynamics are determined by the blood pressure. Blood pressure is the pressure that prevails in a certain section of the heart's activity in the arterial vascular system. If the blood pressure is too high, vessel walls or organs are damaged. Low blood pressure results in slower blood flow. The result is a reduced blood flow to tissues and organs. The blood pressure is also regulated depending on the state of the blood vessels.

Cardiac output and the viscosity of the blood also play a role. Cardiac output is the volume of blood that the heart delivers into the bloodstream per minute. The blood viscosity is the viscosity of the blood. It depends, among other things, on the content of blood cells, the deformability of the red blood cells and the aggregation of the red blood cells. Temperature and the flow rate, which in turn depend on the state of the vessels and also on blood pressure, also influence the viscosity of the blood. The body can regulate the blood flow to the individual organs by changing individual parameters. The aim is that the needs of each individual organ are optimally covered.

The regulation also ensures that, despite the pressure differences between the ejection phase (systole) and the filling phase (diastole) of the heart, most of the blood flows evenly through the body. The wind chamber function of the main artery (aorta) also ensures this even blood flow. The aorta expands during systole. This way, it absorbs some of the blood that is thrown out. During the diastole it contracts and the collected blood flows into the vascular system. If the vessels did not react with this elastic expansion, the blood would always flow through the body in bursts.

The blood pressure wave moves through the body in a young person at an average of six meters per second. In the elderly, this time doubles to twelve meters per second due to the lower vascular elasticity.

The blood flow in the arteries depends to a large extent on the pumping capacity of the heart. Other mechanisms play a role in the veins. The venous valves, for example, are important here. They prevent the blood from flowing back. The surrounding muscles also use muscle pumps to ensure that the venous blood can flow back from the periphery to the heart.

Illnesses & ailments

A disturbed blood flow in the arterial system leads to an insufficient supply of the organs and tissues with oxygen and nutrients. A disease that is caused by a disturbed blood flow is for example peripheral arterial occlusive disease (PAD). It is caused by a progressive occlusion of the arteries in the leg or arm. As a result of arteriosclerosis, the blood in the affected vessels can no longer flow undisturbed. There is an undersupply of the legs or arms. In stage I of the disease, patients usually do not yet notice the disturbed blood flow. In stage II, intermittent claudication, they develop discomfort when walking. In stage IIb, the symptom-free walking distance is less than 200 m. Stage III is even accompanied by pain at rest. In stage IV, ulcers and necrosis develop due to the insufficient supply.

The counterpart to PAOD in the venous system is chronic venous insufficiency. Due to a pathological change in the leg veins, drainage obstructions and microcirculation disorders develop in the area of ​​the feet and lower legs. The chronic venous insufficiency is caused by an increase in pressure in the leg veins. The pressure can rise, for example, due to thrombosis in the leg veins, a missing muscle pump or a malfunction of the venous valves. The disturbed blood flow causes edema to develop on the lower legs. Dark blue skin changes are also visible. Stage two is accompanied by hemosiderosis and purpura on the skin of the lower legs. This leads to congestive eczema and a blue coloration of the skin. The end stage of chronic venous insufficiency is the leg ulcer. It is a deep and weeping wound on the lower leg. The trigger is often a minor injury that cannot heal due to the impaired blood flow.

A leg ulcer also occurs more frequently in diabetes mellitus. Here, too, the cause lies in a disruption of the blood flow. The course of diabetes mellitus leads to both disturbed microcirculation and disturbed macrocirculation.