Arteries and Veins are very different !

Usually we think that arteries and veins are just two types of blood vessels which carry deoxygenated and oxygenated blood. If you also think same then you are wrong. Actually there are three types of blood vessels: Arteries, Veins and Capillaries. Our blood oxygen level don't define the difference between arteries and veins. The actual difference between these blood vessels is a lot more.

Confusion about Definition of Arteries and Veins

Most of the people think that veins carry deoxygenated blood, while arteries carry oxygenated blood. But this assumption is totally wrong, as Pulmonary Artery carry deoxygenated blood and Pulmonary Vein carry Oxygenated blood. The correct definition of Artery is "a blood vessel that takes blood away from heart", and the correct definition of Vein is "a blood vessel that takes blood back to heart". 

In Diagrams arteries are usually painted red and veins are painted blue because veins appear blue through pale skin, but the blood inside veins is actually dark red. Arteries and veins seen during surgery often looks identical.

Apart from direction of blood, is there any other difference between Artery and Vein ?

Most of us think that "from heart" and "to heart" is the only difference between Artery and Vein, while there is much more than that. The basic structure of these two types of blood vessels is very different. 

If all arteires, veins and capillaries are connected end-to-end then they can circle the earth around 4 times, i.e. 100,000 miles. Don't forget that capillaries are also a part of this this assumption which account for most of this length.

Here are some important differences between arteries and veins:

• Blood flows more forcefully in arteries, while that pressure is less in veins. More force of blood in arteries makes them an adequate place to measure pulse rate, as the pulse of blood can be easily felt in them.
• Most of the veins have valves to stop the blood from flowing backwards, while there is no such valves in arteries. These valves are helpful in working against gravity, such as legs which are very far from heart.
• Our arteries have thicker walls as they bear more pressure of blood coming forcefully from heart.
• Two layers of "elastic lamina" are present in arteries, which are either thin or absent in in veins. It provides extra elasticity to arteries.
• Blood pressure in veins is always lower than arteries.
• Arteries are usually deep in skin, while veins are superficial.
• If a vein is cut then it creates a blood pool, while if an artery is cut then it creates a fountain of blood.
• Cross section of artery is usually circular, while that of vein tends to flatten out.
• Among blood vessels neither arteries nor veins are the thinner-most. The thinner-most are the capillaries, which are around one-third of thickness of a human hair. Capillaries are a web of blood vessels between an artery and a vein. Their thickness is so less that RBC pass through them in a single row.

Usually people think that veins of body builders are larger than other people, while the truth is that body builders have less subcutaneous fat and their pumped muscles under the veins pushes veins outwards. Thus it gives a bulgy look to the same veins.