Blood Flow: Function, Tasks, Role & Diseases

Blood flow is the movement of blood in the body’s circulatory system. Blood flow is influenced by various conditions in the body.

What is blood flow?

Blood flow is understood as the movement of blood in the body’s circulatory system. Blood is a fluid of the body that consists of special blood cells and liquid blood plasma. Blood distributes throughout the body via the circulatory system. The blood circulation begins at the heart. Various blood vessels, such as arteries, arterioles and capillaries, distribute the oxygen-rich blood throughout the body. Venules and veins transport the deoxygenated blood back to the heart. The movement of blood in blood vessels is called blood flow. Blood flow is influenced by various factors. For example, it depends on blood pressure, the viscosity of the blood and the resistance of the blood vessels. Basically, however, blood flow follows the laws of hemodynamics. Hemodynamics deals with the flow techniques of blood. Blood flow affects the functionality of the body. Tissues that receive too little oxygen due to impaired blood flow can no longer function properly. Thus, various diseases can develop. Serious diseases, such as heart attack or stroke, are also based on a disturbance of blood flow.

Function and task

Hemodynamics is determined by blood pressure. Blood pressure is the pressure that prevails in the arterial vascular system during a particular segment of cardiac activity. Blood pressure that is too high causes damage to vessel walls or organs. Too low blood pressure results in slower blood flow. Reduced blood flow to tissues and organs is then the result. Blood pressure is also regulated depending on the vascular condition. The cardiac output and the viscosity of the blood also play a role. Cardiac output is the volume of blood that the heart delivers to the bloodstream per minute. Blood viscosity is the viscosity of the blood. It depends, among other things, on the content of blood cells, on the deformability of red blood cells and on the agglomeration of red blood cells. The viscosity of blood is also influenced by temperature and flow velocity, which in turn depends on the condition of the blood vessels and also on blood pressure. By changing individual parameters, the body can regulate the blood flow to individual organs. The aim is to ensure that the needs of each organ are optimally met. Regulation also ensures that, despite the differences in pressure between the ejection phase (systole) and the filling phase (diastole) of the heart, the blood flows through the body mostly evenly. This even blood flow is also ensured by the windkessel function of the aorta. During systole, the aorta expands. As a result, it absorbs some of the ejected blood. During diastole, it contracts and the collected blood flows into the vascular system. If the vessels did not respond with this elastic expansion, the blood would always flow intermittently through the body. In a young person, the blood pressure wave moves through the body at an average rate of six meters per second. In the elderly, this time doubles to twelve meters per second due to reduced vascular elasticity. Blood flow in the arteries depends to a large extent on the pumping action of the heart. In the veins, other mechanisms play a role. The vein valves, for example, are important here. They prevent the blood from flowing back. The surrounding muscles also ensure via muscle pump that venous blood can flow back to the heart from the periphery.

Diseases and ailments

Impaired blood flow in the arterial system leads to a lack of oxygen and nutrient supply to organs and tissues. For example, one disease caused by impaired blood flow is peripheral arterial disease (PAVD). It is caused by a progressive occlusion of the leg or arm arteries. As a result of arteriosclerosis, the blood can no longer flow freely in the affected vessels. This leads to 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 symptoms when walking. In stage IIb, the symptom-free walking distance is less than 200 meters. Stage III is even accompanied by pain at rest.In stage IV, ulcers and necrosis develop due to the undersupply. The counterpart to pAVK in the venous system is chronic venous insufficiency. Due to a pathological change in the leg veins, outflow obstructions and microcirculation disorders develop in the area of the feet and lower legs. Chronic venous insufficiency is caused by an increase in pressure in the leg veins. The pressure can increase, for example, due to thromboses in the leg veins, due to a lack of muscle pump or due to a malfunction of the venous valves. Due to the disturbed blood flow, edema develops on the lower legs. Dark blue skin changes also become visible. Stage two is associated with hemosiderosis and purpura on the skin of the lower legs. There is stasis eczema and blue discoloration of the skin. The final stage of chronic venous insufficiency is leg ulcer. This is a deep and weeping wound on the lower leg. It is often triggered by a small injury that cannot heal due to impaired blood flow. Ulcus cruris also occurs more frequently in diabetes mellitus. Here, the cause is also a disturbance of the blood flow. In its course, diabetes mellitus leads to both disturbed microcirculation and disturbed macrocirculation.