Blood vessels are a part of the circulatory system of the body that transport blood. They supply blood to all the organs, tissues, and cells of the body. They are present all over the body and are of three types – arteries, veins, and capillaries. The arteries carry oxygenated blood away from the heart. Veins carry deoxygenated blood from the capillaries to the heart. Capillaries, the smallest blood vessels, enable the exchange of nutrients, waste substances, chemicals, and water between the tissues and the blood. Together, all these form a complex network of the circulatory and microcirculatory system. Arteries carry oxygenated blood except for the pulmonary artery. They appear rounded and have thick muscular walls. This enables them to resist the high pressure of blood flow. The largest artery is the aorta. Arteries then branch out into arterioles and then eventually divide into capillaries. Veins carry deoxygenated blood to the heart except for the pulmonary vein. They appear flattened and are reservoirs of blood. The largest veins are the superior and inferior vena cava. The inner walls of the veins come with valves to prevent back flow of blood when they are circulated against gravity. When these valves do not function properly, it leads to a condition called varicose veins. Veins further divide into venules and join with capillaries. Capillaries are the smallest blood vessels and the body has nearly 100,000 kilometers of capillaries, which help the exchange of nutrients, gases, waste substances, between the blood vessels and tissues. Capillaries come in different types – Continuous capillaries, fenestrated capillaries, and sinusoid capillaries. In people with diabetes and uncontrolled diabetes, the blood vessels tend to get damaged due to high blood sugar levels. High blood sugar levels lead to a reduced level of fatty acid synthase at the cellular level. This reduced fatty acid synthase level in the endothelial cells on the lining of blood vessels leads to an inability to dilate blood vessels. This is attributed to a lack of nitric oxide, a vasodilator. This is called endothelial dysfunction. This is caused due to an increased production of reactive oxygen metabolites, which decrease the bioavailability of nitric oxide. The imbalance in the vasodilating and vasoconstricting properties of blood vessels leads to a host of complications since the arteries and arterioles cannot dilate properly. This leads to diseases like diabetic retinopathy, diabetic nephropathy, heart diseases, and cardiovascular diseases along with an increased uptake of LDL by the endothelial cells of blood vessels leading to plaque formation.