What Are Veins and Why Should I Know About Them?

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What Are Veins?

When you stick your arm out, you may see blue or green lines under the skin running along it. These are veins, a type of blood vessel in the body. Veins hold around 75% of all the blood in the body at any point in time. If you know about arteries, blood vessels which transport oxygen-rich blood to the heart and other major organs, veins can be thought of as their opposite. The primary function of most veins in the body is to transport deoxygenated (oxygen-poor and containing waste material) blood to the kidneys, to undergo filtration so the waste materials can be excreted, or to the lungs, so that carbon dioxide can be expelled from the blood into exhaled air. [1]

Veins are grouped in two circuits according to which part of the body they transport the blood to:
● Pulmonary
○ Pulmonary veins carry oxygenated blood from the lungs to the heart. In the diagram of the heart below, the pulmonary vein (indicated in purple) transports blood back to the heart once it has been oxygenated again.
○ There are only 4 pulmonary veins in the entire vascular system.
● Systemic
○ Systemic veins carry deoxygenated blood from the rest of the body to the heart.
○ All veins beside the 4 pulmonary ones are systemic. [2]

Types of Veins

There are three types of veins, classified according to their depth below the skin:
● Superficial
○ Superficial veins are located closest to the skin, under the subcutaneous layer of fat. Blood moves slower in these veins as they have no surrounding muscle to compress it.
● Deep
○ Deep veins are found along muscles or bones, located further below the skin. If deep veins get blocked, it can cause serious complications (see below).
● Connecting
○ Connecting veins allow blood to flow from superficial veins to deep ones, and are not supposed to flow in the opposite direction (i.e. deep to superficial). [2]

Major Veins You Should Know

Superior and Inferior Vena Cava:

A diagram of the heart and its connected vessels. Taken from Stepwards

The vena cava are the largest veins in the body, and are connected directly to the heart. The superior vena cava transports blood from the upper body (head, neck etc) and the inferior vena cava transports blood from the parts of the body below the heart (legs, trunk etc) to the right atrium (chamber) of the heart.

Jugular Veins

There is a group of large veins in the head and neck – jugular veins. Their main function is to transport deoxygenated blood from the head and neck to the heart. The internal jugular veins, located on both the right and left sides of the neck, are the largest veins in the neck, and thus serves as the main channel to transport deoxygenated blood to the heart from the head. [3] A cut or tear in the jugular vein could be fatal as a large amount of blood can be lost in a very short time.

Hepatic Portal Vein:

The hepatic portal vein carries blood rich in absorbed nutrients from the stomach, intestines, pancreas and spleen to the liver to be detoxified and processed. [4] If it becomes blocked, pressure on the portal vein will increase, causing large veins called varices to appear around the stomach and oesophagus (gullet). This is called portal hypertension. The chief cause of blockage would be cirrhosis (liver scarring) which can happen due to a variety of conditions, including hepatitis or heavy alcoholism. [5]

The varices can bleed easily, and someone with portal hypertension may have gastrointestinal bleeding (black stools or vomiting of blood), and an accumulation of fluid in the abdomen.

Parts of Veins


A diagram comparing the state of valves in healthy and varicose veins. Taken from Desert Vein and Vascular Institute.

Certain veins will have valves, tiny flaps of tissue attached to their inner walls. They passively open to allow blood to flow to the heart and close to prevent backflow of the deoxygenated blood. If the valves are weakened or damaged, deoxygenated blood will be able to flow back towards the organs they were transported from. [6] This happens most often in the legs, assisted by gravity pulling the blood downwards. Hence blood starts pooling or collecting in the legs and feet, known as chronic venous insufficiency. Chronic venous insufficiency will cause swelling and itchiness in your legs or ankles, and in severe cases, discomfort while walking.

It can cause a number of problems such as varicose veins – thick, bulging and twisted darker veins. Varicose veins can cause aching and swelling in the legs; if treatment is not received, the pain will gradually become more severe and take longer to go away even with rest. Varicose veins may also be a cause for cosmetic concern.

Another potential health issue is deep vein thrombosis, where blood clots become stuck in the deep veins, and thus running the risk of bits of the blood clot breaking off and becoming stuck in other important blood vessels (called an embolism). It is especially dangerous if the clot becomes stuck in a blood vessel leading to the lungs (called a pulmonary embolism). The risk of getting DVT increases with age and with some medical conditions which cause increased clotting risk. Being inactive for a prolonged period of time (sitting or standing) also makes it easier to get DVT as the blood circulation is poor, allowing clots to form more easily.

What should I do if I have vein problems?

If you are currently experiencing any of the vein health issues listed above, our vascular specialists are here to help you. Feel free to book an appointment with us today!

6694 6270 (Call)
9898 3595 (WhatsApp)
[email protected] (Email)

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