Superior Mesenteric Vein

What is the superior mesenteric vein?

Your superior mesenteric vein (SMV) is a blood vessel that helps carry blood from your intestines to your liver. It plays an important role in the distribution of blood in your abdomen (belly) and ultimately your entire circulatory system.

A blood clot or other disruptions to blood flow in your SMV can lead to serious complications. Therefore, it’s important to learn about your SMV and how it supports healthy blood flow in your body.

What is the function of the superior mesenteric vein?

Your superior mesenteric vein supports the work of your hepatic portal system (portal venous system). This is a network of veins that drains blood from organs in your belly and sends it to your liver. Your SMV is one of the most important veins in this network because it collects blood from many other veins.

Your SMV is a bit like a tree branch containing many twigs. The twigs are smaller veins that serve as tributaries, carrying blood from nearby organs into your SMV. Together with its tributaries, your SMV drains blood from your:

• Small intestine.
• Large intestine.
• Stomach.
• Pancreas.
• Appendix.

Your superior mesenteric vein then supplies all this blood to your portal vein.

If you imagine your SMV as a tree branch, then you can think of your portal vein as the tree trunk. This trunk is “planted” in your liver through an opening called your liver hilum. Blood in your portal vein drains into your liver. Your liver then filters and processes the blood before sending it into veins that lead to your heart. Then, the blood flows through your heart and lungs and back out to the rest of your body.

Tributaries of the SMV

The chart below lists tributaries of your superior mesenteric vein and what each one drains.

Where is the superior mesenteric vein located?

Your superior mesenteric vein is in your abdominal cavity. This is the large space under your chest and above your pelvis that holds important organs and tissues.

Your SMV begins near your belly button, within the part of your mesentery that connects with your small intestine. (Your mesentery is a double layer of tissue that holds the organs in your belly in place.) Your SMV extends up to your L1 vertebra, which is the top bone in your lumbar spine. There, it connects with your splenic vein to form your portal vein.

Where does the superior mesenteric vein go?

Your superior mesenteric vein travels along the right side of your superior mesenteric artery. This artery delivers oxygen-rich blood to your intestines. Meanwhile, your SMV carries blood that’s lower in oxygen (but rich in nutrients) away from your intestines and toward your liver. Many of the veins and arteries in your body travel alongside each other in this way. Imagine a two-lane highway with traffic moving in opposite directions on either side.

Occasionally, the SMV travels along the left side of a person’s superior mesenteric artery. This anatomical variation can happen in babies born with malrotation. It can also happen if you have a tumor that presses on nearby structures, including blood vessels.

What is the superior mesenteric vein made of?

Like other veins in your body, your SMV has walls made of three layers:

• Outer layer (tunica adventitia), which provides your vein’s shape.
• Middle layer (tunica media), which contains smooth muscle cells that let your vein grow wide or narrow as blood flows through.
• Inner layer (tunica intima), which has a lining of endothelial cells that keep your blood flowing smoothly.

What conditions affect the superior mesenteric vein?

Conditions that can affect your SMV include:

• SMV thrombosis. This is when a blood clot forms in your superior mesenteric vein. Sudden, severe pain in your belly is the most common symptom of acute thrombosis. But some people with subacute or chronic forms have pain that comes and goes over days or weeks, or no symptoms at all. The sooner you receive care, the better your chances of a good outcome.
• Portal hypertension. This is elevated blood pressure in your portal venous system. Causes of portal hypertension include cirrhosis of the liver and blood clots. Portal hypertension can cause life-threatening complications, such as internal bleeding. Treatment manages complications and, in some cases, redirects blood flow to ease pressure in your blood vessels.

A note from Cleveland Clinic

Learning anatomy can be exciting but also overwhelming. Don’t feel like you need to learn the terms and concepts all at once. If you’re learning about your SMV due to a medical diagnosis, remember that your healthcare provider is there to help. Ask them to explain concepts you don’t understand, and write down the key points. The more you learn about the inner workings of your body, the more you’ll feel comfortable talking to your provider about your condition and what you can expect going forward.