Health Advice



Veins are a key player in the body; here’s why

Robert H. Shmerling, M.D., Harvard Health Blog on

Published in Health & Fitness

Blood circulation is vital to our health. Our arteries deliver oxygen, energy-rich nutrients, hormones, immune cells, and other essentials throughout the body. When deliveries are cut off, organs and tissue can be irreversibly damaged within minutes.

But a second part of blood circulation is also vitally important: the return trip. After our arteries deliver the goods, our blood must return to the lungs to pick up more oxygen, stock up on nutrients, get rid of carbon dioxide, and head back to the heart to be pumped out again. In this way, blood is in continuous motion, ensuring organs and tissues get what they need while waste products are removed.

The vessels designed for the return trip are your veins. Read on for answers to questions about how veins work, what can interfere with their ability to work smoothly, and five ways to keep thousands of miles of these blood vessels healthy.

What are veins and what do they do?

Perhaps you haven't thought much about your veins. Or if you have, maybe you focused on varicose veins, those swollen, unsightly purplish vessels that may be visible just beneath the skin of the legs. Or perhaps you had a blood test and the person taking the blood had a hard time finding a “good vein.” But these are just a small part of vein world.

Veins make up a network of connecting tubes throughout the human body, ranging in size from 1 mm (about the size of a pencil point) to 2 cm (about the size of a quarter), that bring blood low in oxygen back to the lungs to reload with oxygen. Then four pulmonary veins carry oxygen-rich blood from the lungs to the heart. (Fun fact: some people have three or five pulmonary veins, but most of us have four.)


Often, major veins are found alongside similarly named arteries, like a highway with cars moving in opposite directions: in the upper arm, for example, the axillary vein lies next to the axillary artery; in the kidney, the renal vein runs alongside the renal artery.

How do veins help keep blood flowing?

Let's start by picturing tiny red blood cells loaded up with oxygen. Now imagine you're a red blood cell that has just traveled from the heart through the arteries to a calf muscle of someone who is jogging. After you drop off the much-needed oxygen and pick up waste products like carbon dioxide, you need to get back to the heart — fast! — because exercising muscles need extra oxygen.

But wait. As you head back to the lungs to load up on more oxygen and release carbon dioxide, there's a steep climb straight up. How can you make it back to the lungs without help?


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