Inferior phrenic artery

The inferior phrenic artery is a paired vessel that primarily supplies blood to the diaphragm. It is one of the first branches of the abdominal aorta or may arise from other nearby arteries.

Location

The inferior phrenic artery originates near the abdominal aorta, just as it passes through the diaphragm at the level of the twelfth thoracic vertebra (T12). It may arise directly from the aorta, the celiac trunk, or the renal arteries, depending on individual anatomical variation. The artery ascends to supply the undersurface of the diaphragm and often gives off small branches to nearby structures, such as the adrenal glands and esophagus. The right and left inferior phrenic arteries are located on either side of the diaphragm, with each artery curving upward along the muscle’s surface to ensure its blood supply.

Structure and Anatomy

Origin

The inferior phrenic artery is a paired artery, meaning there is a right and left artery, each supplying blood to one side of the diaphragm. The origin of the inferior phrenic artery can vary:

• From the Abdominal Aorta: In most cases, the inferior phrenic artery arises directly from the abdominal aorta, just below the diaphragm at the level of the T12 vertebra.
• From the Celiac Trunk: The artery may also originate from the celiac trunk, which branches off the abdominal aorta.
• From the Renal Arteries: Occasionally, the inferior phrenic artery may arise from the renal arteries, which supply the kidneys.
• From a Common Trunk: In some individuals, the right and left inferior phrenic arteries may share a common trunk, arising from the abdominal aorta or celiac trunk.

Course

• Right Inferior Phrenic Artery: The right inferior phrenic artery ascends obliquely to the right, passing behind the inferior vena cava as it moves toward the diaphragm. As it ascends, the artery follows a course posterior to the liver and branches across the undersurface of the right hemidiaphragm.
• Left Inferior Phrenic Artery: The left inferior phrenic artery also ascends obliquely but toward the left. It travels posterior to the esophagus and runs across the undersurface of the left hemidiaphragm. Like its counterpart, it branches out across the diaphragm to ensure a broad distribution of blood.

Branches

The inferior phrenic artery gives off multiple smaller branches as it approaches and supplies the diaphragm:

• Diaphragmatic Branches: The primary branches of the inferior phrenic artery supply the diaphragm’s muscular and tendinous parts. These branches fan out across the inferior surface of the diaphragm, ensuring that the entire muscle is well-supplied with oxygenated blood.
• Adrenal (Suprarenal) Branches: Both the right and left inferior phrenic arteries often give rise to small superior adrenal arteries, which supply the adrenal glands. These branches are responsible for contributing blood flow to the adrenal glands along with the middle and inferior adrenal arteries.
• Esophageal Branches: Particularly from the left inferior phrenic artery, small branches may supply the lower part of the esophagus as it passes through the diaphragm.
• Collateral Branches: Occasionally, the inferior phrenic arteries may contribute to small collateral branches that help supply nearby structures, including parts of the liver, pancreas, and stomach, especially when the blood supply from other sources is compromised.

Relations

• Right Inferior Phrenic Artery:
  • Anteriorly: The right inferior phrenic artery is closely related to the liver, passing just beneath its posterior surface.
  • Posteriorly: It lies behind the inferior vena cava and the right adrenal gland as it travels upward from the aorta.
• Left Inferior Phrenic Artery:
• • Anteriorly: The left inferior phrenic artery lies in relation to the stomach and the lower esophagus, near the esophageal hiatus.
  • Posteriorly: It is related to the left adrenal gland and the kidney, located beneath the diaphragm.

Length and Diameter

The inferior phrenic arteries are relatively short arteries, as they ascend only a few centimeters from their origin to the diaphragm. The diameter of the artery is small compared to other major arteries like the renal or aortic branches, as it supplies only the diaphragm and small portions of nearby structures.

Termination

The inferior phrenic arteries terminate by splitting into multiple small branches that fan out over the inferior surface of the diaphragm. These branches penetrate the muscular and tendinous portions of the diaphragm, ensuring an even distribution of blood. In some cases, the terminal branches contribute to collateral blood flow in nearby structures, such as the liver or adrenal glands.

Anatomical Variations

Variations in the anatomy of the inferior phrenic arteries are relatively common, including:

• Origin Variations: The most frequent variation involves the origin of the inferior phrenic artery. It may arise from the aorta, celiac trunk, renal arteries, or from a common trunk shared by both the right and left inferior phrenic arteries.
• Accessory Arteries: In some individuals, accessory branches may arise from the inferior phrenic arteries to supply additional regions, such as the liver or pancreas.
• Absence or Fusion: On rare occasions, one of the inferior phrenic arteries may be absent, with the other artery compensating by supplying both sides of the diaphragm, or they may share a common trunk before splitting into separate right and left branches.

Blood Supply Regions

The inferior phrenic arteries are responsible for supplying oxygenated blood to the:

• Diaphragm, primarily its undersurface and central tendon.
• Adrenal glands, via small superior adrenal arteries.
• Lower esophagus, particularly through branches from the left inferior phrenic artery.
• Surrounding structures, including occasional contributions to the liver, stomach, and pancreas.

Function

The inferior phrenic artery plays a crucial role in supplying blood to the diaphragm, the primary muscle responsible for breathing. In addition to its role in supporting diaphragmatic function, the artery also supplies blood to nearby structures, including the adrenal glands and esophagus. Below is a detailed breakdown of the functions of the inferior phrenic artery.

Blood Supply to the Diaphragm

The most critical function of the inferior phrenic artery is to provide oxygenated blood to the diaphragm, ensuring it functions effectively as the primary muscle in respiration. The artery’s branches fan out across the diaphragm, supplying both its muscular and tendinous portions. Specific roles include:

• Nourishing Diaphragmatic Muscle: The diaphragm is a dome-shaped muscle that contracts and flattens during inhalation, creating negative pressure that draws air into the lungs. The oxygenated blood supplied by the inferior phrenic artery is essential for maintaining the energy needed for muscle contraction during breathing.
• Maintaining Diaphragmatic Tone: The diaphragm is involved in a wide range of activities beyond normal breathing, such as aiding in coughing, sneezing, laughing, and even stabilizing the core during lifting. The artery ensures that the muscle remains well-nourished and oxygenated during these activities, ensuring endurance and preventing fatigue.
• Supplying the Central Tendon: The central tendon of the diaphragm, a thin but strong aponeurosis, also receives blood from the inferior phrenic artery. This is crucial for maintaining the structure and elasticity of the diaphragm, as the central tendon serves as the point of insertion for the muscle fibers.

Blood Supply to the Adrenal Glands

The inferior phrenic artery contributes to the blood supply of the adrenal glands via small branches known as the superior adrenal arteries. These arteries play an important role in supporting the adrenal glands’ hormone-producing functions:

• Support for Hormone Production: The adrenal glands produce vital hormones, including cortisol, adrenaline, and aldosterone. These hormones regulate metabolism, blood pressure, and the body’s stress response. The blood supplied by the superior adrenal arteries, which branch off from the inferior phrenic arteries, ensures that the adrenal glands have sufficient oxygen and nutrients to sustain their hormone-producing activities.
• Providing Blood to the Adrenal Cortex and Medulla: The adrenal glands consist of two distinct layers—the outer cortex and inner medulla. The superior adrenal arteries supply both regions, ensuring that each has the necessary resources to produce hormones. The cortex produces corticosteroids, while the medulla releases adrenaline and noradrenaline.

Blood Supply to the Lower Esophagus

The left inferior phrenic artery often provides small esophageal branches that supply blood to the lower portion of the esophagus, particularly where the esophagus passes through the diaphragm at the esophageal hiatus. This blood supply supports several important functions:

• Protection of Esophageal Mucosa: The lower esophagus is prone to damage from gastric acid reflux, especially in conditions like gastroesophageal reflux disease (GERD). The blood supplied by the esophageal branches of the inferior phrenic artery helps nourish the mucosal lining of the esophagus, aiding in repair and protecting the esophageal wall from acid damage.
• Maintenance of the Esophagogastric Junction: The blood flow provided by the esophageal branches supports the integrity of the esophagogastric junction, where the esophagus meets the stomach. This region is critical in preventing the backflow of stomach contents into the esophagus, and the artery’s contribution ensures that this junction remains healthy and functional.

Oxygen and Nutrient Delivery

As with all arteries, the primary function of the inferior phrenic artery is to deliver oxygen and nutrients to the tissues it supplies. This process is essential for:

• Cellular Metabolism: The diaphragm, adrenal glands, and lower esophagus are highly active tissues that require a constant supply of oxygen to support cellular respiration and generate energy. The blood provided by the inferior phrenic artery ensures that these cells receive the oxygen and nutrients they need to maintain normal metabolic processes.
• Tissue Repair and Regeneration: The diaphragm, like all muscles, undergoes wear and tear as it contracts and relaxes during breathing. The blood supplied by the inferior phrenic artery supports the repair and regeneration of muscle tissue, ensuring that the diaphragm remains healthy and functional. The same applies to the esophagus, particularly in areas that experience irritation from acid reflux or other stressors.

Contribution to Collateral Circulation

The inferior phrenic artery plays a role in collateral circulation by providing alternate pathways for blood flow to nearby structures, especially in cases where other arteries are compromised. This is particularly important in situations where blood flow to the diaphragm, esophagus, or adrenal glands may be reduced due to blockages or injury.

• Collateral Blood Flow to the Diaphragm: The inferior phrenic arteries form anastomoses with other vessels that supply the diaphragm, such as the superior phrenic arteries (from the thoracic aorta) and the pericardiacophrenic arteries. These connections provide redundancy in blood supply, ensuring that the diaphragm remains oxygenated even if one artery is blocked or damaged.
• Contribution to the Adrenal Glands: In addition to the superior adrenal arteries (from the inferior phrenic artery), the adrenal glands also receive blood from the middle adrenal arteries (from the aorta) and the inferior adrenal arteries (from the renal arteries). The inferior phrenic artery’s contribution helps create a network of vessels that ensures a continuous supply of blood to the adrenal glands, even if one of the other arteries is compromised.

Clinical Significance

The inferior phrenic artery is clinically significant because it supplies blood to the diaphragm, adrenal glands, and lower esophagus. Its importance is highlighted in conditions involving the diaphragm, such as diaphragmatic paralysis or injury, where the artery’s blood supply is crucial for muscle function and recovery. The artery also plays a role in certain cases of adrenal tumors, such as pheochromocytomas, where the superior adrenal branches of the inferior phrenic artery may need to be carefully managed during surgery.

Additionally, the artery can be involved in esophageal and gastric surgeries due to its esophageal branches, which supply the lower esophagus. In cases of vascular diseases, such as aneurysms near the celiac trunk or abdominal aorta, the inferior phrenic artery’s role in collateral circulation becomes important to maintain blood flow to the diaphragm and surrounding structures. Understanding its course and variations is essential in abdominal and thoracic surgeries to prevent complications.