What are Blood Vessels?

Our heart works as a pumping machine through the help of blood vessels, a method better known as circulatory system. These blood vessels are flexible muscular tubes that transport blood to each and every body part. Not only continuous supply of oxygen and nutrients, but discarding waste like carbon dioxide from the body tissues is an essential job of these blood vessels.

Blood vessels can be classified in major 3 types as given below:

1) Veins: Veins are transparent tubes spread around the whole body. They are positioned just under the skin and less strong than arteries. Veins are blood vessels that take blood back to the heart. But there are two types of specific veins namely pulmonary and umbilical veins which transports oxygenated blood to the heart. As fresh oxygen and nutrients gets consumed by the tissues in the body, blood which returns back to heart via veins has very less oxygen and full with waste products to be removed from the body.

The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart. These veins happen to be large near to the heart area.
Majority of veins have equipped with valves to prevent blood flowing in the reverse direction. Veins are of different types as mentioned here:

a) Pulmonary veins deliver oxygen-rich blood from the lungs back to the left atrium to the heart. There are 4 pulmonary veins in total, two from each lung.

b) Systemic veins role is to bring back oxygen-poor blood to the right atrium of the heart from all over body tissues.

c) Superficial veins are situated near to the body skin and have no related arteries. They carry very less blood and serve to drain blood from the skin.

d) Deep veins are deeper in the body and have corresponding arteries. These are normally close to an artery and share the same name like femoral vein is besides the femoral artery. Deep veins transport most of the blood in the body.

e) Perforator veins go through from superficial to the deep veins and their role is to maintain correct blood draining. For example lower limbs and feet veins.

f) Communicating veins are veins that directly connect superficial veins to deep veins.

2) Arteries : Arteries are also a type of blood vessel that carries oxygen-rich blood away from the heart to all of the body's tissues. However the pulmonary arteries carry oxygen-poor blood from the heart to the lungs under low pressure, making these arteries unique.

The largest artery is the aorta, which work like the main high-pressure pipeline connected to the heart's left ventricle. These are divided from the main artery many times and develop into smaller arteries to shunt blood from the heart into all the distant located organs. Subdivision of the main artery into smaller arteries is called arterioles and capillaries. This network of smaller arteries extends throughout the body. Each artery is a muscular tube lined by smooth tissue and has three layers:

a) The intima is the internal layer of a smooth tissue called endothelium.

b) The media is a layer of muscle that helps the arteries to deal with force coming from the heart.

c) The adventitia is the connective tissue attaching arteries to nearby tissues.

3) Capillaries : These are tiny thin blood vessels that connect the smallest arteries (arterioles) and the veins (venules). It is a kind of a tube which has an internal diameter of hair-like thinness. Capillaries have thin walls and form a network throughout the body which lets the oxygen, nutrients and waste products like carbon dioxide to pass through blood and tissue cells.