Middle colic artery

The middle colic artery is a major branch of the superior mesenteric artery (SMA). It arises from the anterior surface of the SMA and is responsible for supplying blood to the transverse colon.

Location

The middle colic artery originates in the upper abdomen, near the level of the first lumbar vertebra (L1), where the superior mesenteric artery emerges from the aorta. From there, the middle colic artery travels upward and anteriorly within the mesocolon, the connective tissue that suspends the colon from the abdominal wall. It divides into right and left branches as it approaches the transverse colon. The right branch typically anastomoses with the right colic artery, and the left branch forms an anastomosis with the left colic artery, which comes from the inferior mesenteric artery. This artery runs along the upper part of the abdominal cavity, following the path of the transverse colon.

Structure and Anatomy

Origin

The middle colic artery arises from the anterior surface of the superior mesenteric artery (SMA). It typically originates at the level of the first lumbar vertebra (L1), just below the origin of the SMA from the abdominal aorta. It is one of the first major branches of the SMA and is directed primarily toward the transverse colon.

Course

After its origin from the superior mesenteric artery, the middle colic artery ascends and runs anteriorly through the transverse mesocolon, which is the fold of the peritoneum attaching the transverse colon to the posterior abdominal wall. The artery courses upward and slightly forward as it approaches the transverse colon.

Branches

As the middle colic artery approaches the transverse colon, it divides into two primary branches:

• Right Branch: This branch travels toward the right side of the transverse colon and anastomoses with the right colic artery. The right branch is responsible for supplying the right half of the transverse colon, including the hepatic flexure, the junction between the ascending colon and transverse colon.
• Left Branch: The left branch of the middle colic artery travels toward the left side of the transverse colon and anastomoses with the left colic artery, which is a branch of the inferior mesenteric artery. This anastomosis is important for supplying the left half of the transverse colon and part of the splenic flexure (the junction between the transverse colon and the descending colon).

Relations

• Anteriorly: The middle colic artery is covered by the transverse mesocolon, and anterior to the transverse mesocolon are loops of small intestine.
• Posteriorly: It lies in front of the duodenum and pancreas, particularly the head of the pancreas, as it courses within the mesocolon.
• Medially: Medial to the middle colic artery is the superior mesenteric artery, from which it arises.
• Laterally: The artery runs laterally toward both sides of the transverse colon, with its right and left branches extending toward their respective areas.

Length and Diameter

The middle colic artery is relatively short in its main trunk, but its branches extend along the transverse colon. The length and diameter of the artery can vary depending on individual anatomy, but it is typically smaller in caliber compared to the superior mesenteric artery itself. It provides significant blood supply to the transverse colon and its surrounding areas.

Anastomoses

The middle colic artery plays an essential role in the formation of anastomoses with neighboring arteries:

• Right Colic Artery: The right branch of the middle colic artery anastomoses with the right colic artery, which supplies the ascending colon and hepatic flexure. This connection ensures that both the right side of the transverse colon and the hepatic flexure receive an adequate blood supply.
• Left Colic Artery: The left branch of the middle colic artery anastomoses with the left colic artery from the inferior mesenteric artery, which supplies the descending colon and the splenic flexure. This connection provides collateral blood flow to the left side of the transverse colon and the splenic flexure.

These anastomotic connections are important for maintaining the blood supply to the transverse colon and nearby regions, especially in cases of vascular disruption or surgery.

Relations to Other Vessels

• Superior Mesenteric Vein: The middle colic artery runs adjacent to the superior mesenteric vein, which parallels the superior mesenteric artery. The vein drains blood from the transverse colon and other regions into the portal vein.
• Inferior Mesenteric Artery: The left branch of the middle colic artery anastomoses with the inferior mesenteric artery’s left colic branch, creating a key connection between the SMA and IMA circulatory systems.

Termination

The middle colic artery terminates by dividing into its right and left branches, which further supply blood to the transverse colon. These branches continue their course by anastomosing with the right and left colic arteries, ensuring a continuous blood supply along the length of the transverse colon and into the neighboring regions.

Anatomical Variations

• Absent Middle Colic Artery: In some individuals, the middle colic artery may be absent or underdeveloped, with the transverse colon receiving its blood supply from anastomoses between the right and left colic arteries.
• Variation in Branching Pattern: The branching pattern of the middle colic artery can vary between individuals. In some cases, the right branch may be dominant, while in others, the left branch may be more prominent.

Function

The middle colic artery plays a vital role in supplying oxygenated blood to the transverse colon, ensuring that the colon receives the necessary nutrients and oxygen to perform its functions in digestion and absorption. Below is a detailed breakdown of its specific functions based on the regions it supplies and its connections to other arteries.

Blood Supply to the Transverse Colon

The primary function of the middle colic artery is to supply blood to the transverse colon, which is the longest section of the colon. This section of the large intestine is responsible for:

• Absorption of Water and Electrolytes: The transverse colon continues the process of absorbing water and electrolytes from the digestive contents as they move through the colon. The blood supply from the middle colic artery ensures that the epithelial cells lining the colon receive sufficient oxygen and nutrients to perform this absorptive function effectively.
• Support for Colonic Muscle Contractions: The smooth muscles of the transverse colon require a continuous blood supply to maintain peristaltic movements, which help move food material along the digestive tract. The middle colic artery provides oxygenated blood to support these contractions, which are essential for moving digested material through the colon.

 Blood Supply to the Hepatic Flexure

The right branch of the middle colic artery extends toward the hepatic flexure, where the transverse colon curves downward to become the ascending colon. The hepatic flexure marks a key point in the movement of contents from the transverse to the ascending colon. The middle colic artery ensures:

• Adequate Oxygenation: The hepatic flexure receives blood from both the right colic artery and the right branch of the middle colic artery. This dual supply helps maintain a sufficient blood flow to support tissue metabolism and muscle function in this region.
• Support for Flexure Movement: The hepatic flexure requires robust blood supply for the smooth muscle contractions that help propel digested material around the bend and into the ascending colon. The middle colic artery plays a role in supporting these movements.

Blood Supply to the Splenic Flexure

The left branch of the middle colic artery supplies blood to the left portion of the transverse colon and contributes to the blood supply of the splenic flexure, the point where the transverse colon curves downward to become the descending colon. The splenic flexure is a critical area because it is a watershed region, meaning it is at the junction of blood supply from both the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA). The middle colic artery’s left branch helps ensure:

• Continuous Blood Flow to the Splenic Flexure: The left branch anastomoses with the left colic artery from the inferior mesenteric artery (IMA), providing collateral circulation to this area. This dual blood supply is crucial because the splenic flexure is vulnerable to ischemia if either artery is compromised.
• Maintaining Flexure Function: The splenic flexure’s smooth muscle contractions and tissue health depend on the blood supply from both the middle colic artery and the left colic artery. The middle colic artery helps prevent ischemia by providing oxygen and nutrients to this critical junction.

Anastomotic Support and Collateral Circulation

One of the key functions of the middle colic artery is its role in forming important anastomoses with other arteries, providing collateral blood supply to the colon. These anastomotic connections ensure that blood flow continues even if one artery is compromised:

• Anastomosis with the Right Colic Artery: The right branch of the middle colic artery anastomoses with the right colic artery, which supplies the ascending colon. This connection ensures that the right side of the transverse colon and the hepatic flexure receive a continuous blood supply from multiple sources.
• Anastomosis with the Left Colic Artery: The left branch of the middle colic artery anastomoses with the left colic artery, a branch of the inferior mesenteric artery (IMA). This connection is particularly important at the splenic flexure, a watershed area between the SMA and IMA circulatory systems, ensuring continuous blood flow even if one artery is obstructed.

Contribution to the Marginal Artery of Drummond

The middle colic artery contributes to the formation of the marginal artery of Drummond, which is a continuous arterial vessel that runs along the inner border of the colon, providing collateral circulation between the superior mesenteric artery and the inferior mesenteric artery. The marginal artery helps to:

• Ensure Continuous Blood Supply Along the Colon: The middle colic artery’s contribution to the marginal artery supports continuous blood flow along the length of the transverse colon and into neighboring sections of the colon.
• Facilitate Surgical Safety: During surgeries involving the colon, such as resections, the marginal artery serves as a safeguard to maintain blood flow to the colon if other arteries are ligated or obstructed. The middle colic artery’s connection to this system is vital for protecting the transverse colon from ischemic damage.

Oxygen and Nutrient Delivery

As with other arteries in the gastrointestinal system, the primary function of the middle colic artery is to deliver oxygen and nutrients to the tissues it supplies. The blood supplied by the middle colic artery supports:

• Cellular Metabolism: The epithelial cells, smooth muscle cells, and immune cells in the transverse colon require oxygen and nutrients to perform their functions. This includes absorbing water, maintaining peristalsis, and defending against pathogens. The middle colic artery ensures these cells receive the necessary resources to maintain their metabolic activities.
• Tissue Repair and Maintenance: The colonic epithelium undergoes constant wear and tear from the passage of food and waste material. The blood supply from the middle colic artery supports the rapid regeneration and repair of these tissues, ensuring that the colon remains functional and intact.

Clinical Significance

The middle colic artery is clinically significant due to its vital role in supplying blood to the transverse colon and the splenic and hepatic flexures. In surgical procedures such as colectomies or other bowel resections, the middle colic artery must be carefully navigated to avoid compromising blood flow to the transverse colon. Its anastomotic connections with the right and left colic arteries provide crucial collateral circulation, especially in the splenic flexure, which is a watershed area at risk of ischemia.

In conditions like mesenteric ischemia or vascular disease, blockage or disruption of the middle colic artery can result in ischemic damage to the transverse colon. Additionally, during surgical management of colon cancer, understanding the artery’s anatomy and its anastomoses helps to maintain adequate blood supply to the remaining colon segments.