Superior Mesenteric Vein: Anatomy, Location and Function

What is the superior mesenteric vein?

The superior mesenteric vein (SMV) is a large vein in the abdomen that plays a crucial role in the digestive system. It drains blood from parts of the gastrointestinal tract, including the small intestine, cecum, ascending colon, and part of the transverse colon.

The SMV runs alongside the superior mesenteric artery and eventually joins with the splenic vein to form the portal vein. The portal vein then transports the nutrient-rich blood from the intestines to the liver for processing and detoxification.

In essence, the SMV is an important component of the venous drainage system of the digestive organs.

What is the function of the superior mesenteric vein?

The superior mesenteric vein (SMV) has the critical function of draining blood from the intestines and portions of the gastrointestinal tract. Specifically, it carries nutrient-rich, deoxygenated blood from the small intestine (jejunum and ileum), cecum, ascending colon, and part of the transverse colon, as well as from the pancreas.

Once the blood is collected by the SMV, it joins the splenic vein to form the portal vein, which delivers this blood to the liver. In the liver, nutrients are processed, toxins are detoxified, and waste products are filtered before the blood continues to the systemic circulation. Thus, the SMV is integral to the body's nutrient absorption and waste removal processes.

Tributaries of the SMV

The superior mesenteric vein (SMV) has several tributaries that drain blood from various parts of the gastrointestinal tract and associated organs. The major tributaries of the SMV include:

● Right gastroepiploic vein - Drains blood from the greater curvature of the stomach.

● Anterior and posterior inferior pancreaticoduodenal veins - Drain blood from the pancreas and the duodenum.

● Jejunal and ileal veins - Drain blood from the jejunum and ileum (parts of the small intestine).

● Ileocolic vein - Drains blood from the ileum, cecum, and appendix.

● Right colic vein - Drains blood from the ascending colon.

● Middle colic vein - Drains blood from the transverse colon.

These tributaries converge into the SMV, which then merges with the splenic vein to form the portal vein, continuing the process of transporting blood to the liver for filtration and nutrient processing.

Where is the superior mesenteric vein located?

The superior mesenteric vein (SMV) is located in the abdominal cavity, running parallel and adjacent to the superior mesenteric artery (SMA).

Key landmarks for its location:

■ Origin:

 The SMV begins in the lower right quadrant of the abdomen, collecting blood from the small intestine and parts of the large intestine.

■ Course: 

It ascends vertically along the right side of the superior mesenteric artery. The vein runs behind the neck of the pancreas.

■ Termination:

 The SMV joins with the splenic vein posterior to the pancreas to form the portal vein, which then carries blood to the liver.

The SMV is part of the larger portal venous system and lies anterior to the third part of the duodenum as it ascends through the abdomen.

Where does the superior mesenteric vein go?

The superior mesenteric vein (SMV) ascends through the abdomen and eventually merges with the splenic vein to form the portal vein.

Pathway:

● After collecting blood from the intestines and other organs, the SMV runs upward, behind the neck of the pancreas.

● It then meets the splenic vein, usually just behind the pancreas, where the two veins join to form the portal vein.

Final Destination:

The portal vein carries the blood, which is rich in nutrients but low in oxygen, to the liver. In the liver, this blood undergoes detoxification and nutrient processing before being released into the systemic circulation. Hence, the SMV plays a vital role in directing blood to the liver as part of the portal venous system.

What is the superior mesenteric vein made of?

The superior mesenteric vein (SMV), like other veins in the body, is made up of several layers of tissue that are designed to carry blood back toward the heart. These layers include:

■ Tunica intima (inner layer): 

This is a thin layer of endothelial cells that line the inside of the vein. It provides a smooth surface for blood to flow and plays a role in preventing blood clots.

■ Tunica media (middle layer): 

This layer is made of smooth muscle and elastic tissue. In veins, the tunica media is thinner compared to arteries, as veins operate under lower pressure. The smooth muscle helps to maintain the vein’s shape and assists in controlling blood flow by contracting or relaxing as needed.

■ Tunica adventitia (outer layer): 

This is the outermost layer and is composed of connective tissue, including collagen and elastic fibers. It provides structural support and flexibility to the vein, helping to protect it from overexpansion.

Overall, the SMV is composed of these layers, working together to transport nutrient-rich, deoxygenated blood from the intestines and other organs to the liver.

What conditions affect the superior mesenteric vein?

Several conditions can affect the superior mesenteric vein (SMV), impacting its function and the blood flow through it. These include:

● Superior Mesenteric Vein Thrombosis (SMVT):

 This is a condition where a blood clot forms in the SMV. It can lead to intestinal ischemia (reduced blood flow to the intestines), causing abdominal pain, nausea, and potentially severe complications if not treated promptly.

● Mesenteric Ischemia:

 This condition occurs when there is a reduction in blood flow to the intestines, often due to clotting or narrowing of the SMV or its tributaries. It can result from SMV thrombosis or embolism, leading to pain, vomiting, and in severe cases, bowel necrosis.

● Portal Hypertension:

 Elevated blood pressure in the portal venous system can affect the SMV. It is often caused by liver cirrhosis or other liver diseases, leading to complications such as esophageal varices or ascites.

● Tumors:

 Tumors in the abdomen, particularly those involving the pancreas or intestines, can compress or invade the SMV, affecting its function and blood flow.

● Infections or Inflammatory Conditions:

 Conditions such as pancreatitis or Crohn's disease can cause inflammation that affects the SMV, leading to thrombosis or compromised blood flow.

These conditions can have significant effects on digestive health and require medical evaluation and treatment.