The peripheral blood vessels that people often refer to mainly include three parts: arteries, veins and lymphatic vessels. Arterial blood flowing in the arterial vessels is arterial blood rich in nutrients and oxygen, which is necessary to maintain various normal physiological functions of the human body. If the blood vessels are narrowed or occluded, the blood supply to local tissues is reduced, and that tissue will cause pain or necrosis. The venous blood flowing in the venous vessels contains many wastes produced by the body’s metabolism and is expelled from the body through the kidneys and other organs, and poor venous reflux or the formation of thrombus often causes tissue edema or dysfunction. The blood vessels connecting arteries and veins are capillaries, which are widely distributed and interconnected, forming a capillary network. The capillary wall is highly permeable, and many substances can be exchanged through the capillaries. After the exchange of substances, the arterial blood enters the body tissues with nutrients, and then takes away the waste produced by the body’s metabolism and turns into venous blood. The lymphatic vessels are another channel for the return of body fluids and assist the veins in returning lymphatic fluid to the right atrium. Poor lymphatic return or leakage out can cause tissue swelling, lymphatic leakage, celiac disease and other pathologies.