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Overview of blood vessels

Tirohanga whānui ki ngā ia toto

Blood vessels consist of arteries, veins and capillaries.


Most arteries carry blood away from your heart and deliver oxygen to the tissues around your body. Muscles within your artery walls relax and constrict to allow more, or less blood to flow.

Arteries are found in every part of your body. All arteries can be affected by arterial disease. In some parts of your body, arterial disease has little or no affect and doesn’t need treating. In other parts, such as your heart, arterial disease can cause life-threatening conditions and needs treating.

Arteries narrowing or getting blocked due to hardening of the arteries' walls is the most common form of arterial disease. This is called atherosclerosis (a-ther-oh-scler-oh-sis). Atherosclerosis can cause heart disease, strokes, peripheral vascular disease and a lack of blood supply to a limb that can damage the limb.

Atherosclerosis can also weaken an artery's wall so that it widens or bulges. This is called an aneurysm (an-yur-ism). Aneurysms can burst and bleed or block and stop blood flow. When they burst or block suddenly, it can be a life- or limb-threatening emergency, which needs emergency treatment.

An arterial wall can tear along its length without bursting. This is called a dissection. A dissection is not very common but it's very painful and affects the blood supply to major organs. It can be life-threatening without emergency treatment.

A dissection is a complicated disease most commonly caused by high blood pressure. Some genetic (hereditary) diseases can also cause a weakness in the arterial wall.


Most veins return blood back to your heart. Your veins also have muscles but less muscles than your arteries. The muscles within your veins allow them to get larger or smaller in response to heat, cold or injury. One-way valves inside your veins stop your blood from flowing backwards.

Problems with veins can be caused by blood flow issues. Blood clotting in your body's deep veins is called deep vein thrombosis (DVT). Sometimes the clot can move and travel in your bloodstream to your lungs, causing a pulmonary embolism (PE) which can be life threatening.

Other problems with veins include thrombophlebitis (throm-bo-fle-by-tis), which is clotting in superficial veins (near the surface of your skin) and venous insufficiency, which is caused by problems with the valves allowing blood to flow in the wrong direction. Veins can also become swollen and twisted known as varicose veins.


Capillaries are tiny blood vessels that connect the arteries and veins in your tissues. They deliver the oxygen and nutrients that make your body function. They also remove carbon dioxide and other waste products that are removed (excreted) or recycled (metabolised) by organs such as your liver, lungs, kidneys and spleen.

Written by HealthInfo clinical advisers. Last reviewed August 2022.


Page reference: 403761

Review key: HIBLV-403653