March 11, 2014
By Robert H. Shmerling M.D.
Beth Israel Deaconess Medical Center
Perhaps you've heard statements like this before:
- High cholesterol can lead to hardening of the arteries.
- My cousin had blood clots so he took a blood thinner to prevent them from going to his lungs.
- A heart attack may complicate atherosclerosis.
- Cardiovascular disease is the number one killer of adults in the United States.
All of the conditions mentioned above have something in common: They are blood vessel diseases that block blood flow in some way.
When blood flow is interrupted, the body's tissues can't get the nutrients (including oxygen) they need. And waste products don't get removed from tissues.
It's easy to confuse the various blood vessel conditions. So here's a closer look at them and how doctors talk about them.
A Quick Anatomy Lesson
Understanding anatomy and function are the first steps to understanding the various blood vessel problems.
For example, a clot in a leg vein almost never causes a stroke. But a clot in a neck artery often does. Knowing a bit about the anatomy makes this logical (rather than just a random fact to memorize).
So, consider the following:
- If all of the blood vessels in the body were removed and put end to end, they would stretch out 60,000 miles. Each major vessel has its own name (such as radial artery or femoral artery). And different vessel types have different names (such as skin capillary or kidney arteriole).
- Think of all these blood vessels as forming a loop. Let's track it, starting at the left side of the heart:
- The left side of the heart receives oxygen-rich blood from the lungs.
- When the heart pumps, blood exits the heart through the aorta (the largest artery) to tissues throughout the body.
- The aorta leads to arteries in the tissues. Arteries branch into smaller blood vessels called arterioles. These in turn branch into even smaller blood vessels called capillaries. This network delivers oxygen and picks up carbon dioxide from the blood.
- Capillaries lead to small veins (called venules) and larger veins that travel back to the right side of the heart.
- The right side of the heart pumps blood into the lungs to drop off the carbon dioxide and to pick up more oxygen.
- This oxygen-rich blood flows from the lungs to the left side of the heart and the cycle repeats.
- Here's a trick to avoid confusing arteries and veins: Arteries take blood away from the heart (both words starting with a); so, veins must bring it back. And it follows that arteries are carrying oxygen-rich (bright red) blood and veins carry oxygen-poor (bluish or dark red) blood. (The one major exception to this is the large vessels around the lungs: the pulmonary artery takes oxygen-poor blood from the right ventricle to the lungs and the pulmonary vein takes oxygen-rich blood from the lungs to the left atrium.)
- While a blockage in any blood vessel can be dangerous, a blocked artery is usually worse than a blocked vein. That's because interrupting oxygen flow can cause tissue damage within minutes. Still, a vein clot can also cause major trouble. One example is when a blood clot in a leg vein travels to the lungs, a condition that is potentially fatal.
- Clots are the most common causes of vessel blockage. There are two main types:
- Embolic – A clot travels some distance through the blood vessel and suddenly blocks blood flow (especially if a person has certain abnormal heart rhythms such as atrial fibrillation).
- Thrombotic – A narrowing develops in the wall of the blood vessel due to the accumulation of cholesterol, inflammatory cells and blood cells (especially common with diabetes, high blood pressure or high cholesterol).
Common Examples of Conditions and Diseases
Imagine you're a blood cell traveling out of the heart through the aorta. If you took an early off-ramp, you might wind up in a coronary artery. These arteries supply the heart muscle; a blockage here can cause a heart attack.
If, instead, you stayed in the aorta a bit longer and then chose a branch heading "north," you might enter the brain where a blockage can cause a stroke.
If you stayed in the aorta and took a later exit, you might reach the arm and hand where a blocked artery can cause gangrene in a finger.
Your fellow red blood cells, which were still in the aorta, could travel on to the spleen, intestine, kidney or legs. Here, a blockage might cause damage to one of these organs or tissues. If it's a small blockage, a person might not even know it. If it's large, you might become quite ill and need immediate treatment (including surgery) to open up the blockage and/or remove the dead tissue.
Meanwhile, if a vein is blocked, there is typically swelling, pain and, perhaps, redness in the area. This tends to be less dramatic than an artery blockage. One reason is that blood trying to flow through a blocked vein can often be diverted to another vein that's headed toward the same ultimate destination. However, the pressure that builds up from a blocked vein can cause complications, so prompt diagnosis and treatment are important.
Examples of vein blockages include:
- Leg vein clot (deep vein thrombosis)
- Liver vein clot (called hepatic vein thrombosis or "Budd-Chiari Syndrome")
- Kidney vein clot (called renal vein thrombosis)
"Collaterals" Can Prevent Collateral Damage
When an artery slowly narrows, blood can often find an alternate route. (New or enlarged channels, called collaterals, may develop on their own over time. But if the blockage occurs suddenly, as with an embolus, there isn't time for collaterals to develop. Often, the difference between a fatal heart attack and a bit of chest pain is the presence of collaterals.
Coronary artery bypass surgery uses this same concept. Surgeons remove a small (and nonessential) vein from the leg and use it to divert blood around the narrowed portion of a blocked coronary artery. The surgery essentially creates a collateral blood vessel.
Tumors Need Blood Vessels, Too
Tumors need an adequate blood supply to grow or survive. Several decades ago, researchers discovered that many tumors make and release chemical messengers that stimulate the formation of new blood vessels. This has recently led to the first approved anti-cancer drug that prevents blood vessel formation directed by tumors. It's called bevacizumab (Avastin). It is approved for the treatment of several cancers, including certain colon and lung cancers.
The Bottom Line
It's a minor miracle (or perhaps a major one) that the 60,000 miles of blood vessels in our bodies do their job so well for so long. The major problems that can complicate disease in our vascular system confirm how important these conduits are.
It's worth making an effort to prevent cardiovascular disease. This means not smoking, eating well, exercising, and keeping your cholesterol, blood sugar and blood pressure normal.
Talk with your doctor about how to prevent cardiovascular disease. The talk will go a lot better now that you know the difference between arteries and veins. If you're confused about something she says, ask for more information. As always, that's the best way to know what your doctor is saying.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.