Inferior rectal artery

The inferior rectal artery is a branch of the internal pudendal artery that supplies blood to the lower part of the rectum and the anal canal.

Location

The inferior rectal artery arises from the internal pudendal artery within the ischioanal fossa. It originates shortly after the internal pudendal artery exits the greater sciatic foramen and re-enters the pelvis through the lesser sciatic foramen. From the ischioanal fossa, the inferior rectal artery travels medially across the fossa toward the anal canal and the lower part of the rectum. It runs along the walls of the anal canal and anastomoses with branches from the middle rectal artery and superior rectal artery, forming a network of vessels that supply the anorectal region.

Structure and Anatomy

Origin

The inferior rectal artery is a branch of the internal pudendal artery, which itself is a branch of the internal iliac artery. It originates after the internal pudendal artery exits the pelvis through the greater sciatic foramen and re-enters through the lesser sciatic foramen into the ischioanal fossa. It typically arises just lateral to the anal canal and the lower rectum.

Course

Once the inferior rectal artery branches from the internal pudendal artery, it travels medially across the ischioanal fossa, a fat-filled space located on either side of the anal canal. As it courses through this fossa, the artery runs towards the anal canal and lower rectum, supplying blood to these structures.

The artery passes within the ischioanal fossa deep to the levator ani muscle, one of the major muscles of the pelvic floor, which helps support the pelvic organs and maintain continence. The artery runs along the lateral walls of the anal canal, giving off small branches that supply the sphincter muscles, mucosa, and skin in this region.

Branches

The inferior rectal artery gives rise to several smaller branches as it travels toward the anal canal. These branches supply blood to various structures in the anorectal region, including:

• Sphincter Muscles: The artery provides blood to both the external anal sphincter and portions of the internal anal sphincter. These muscles are responsible for controlling the passage of stool and maintaining continence.
• Anal Canal Mucosa: The artery supplies the mucosa of the anal canal, ensuring that this delicate lining receives adequate blood for tissue health and repair.
• Perianal Skin: The artery gives off cutaneous branches that supply the skin surrounding the anus, contributing to the vascularization of the perineal and anal regions.

Termination

The inferior rectal artery terminates by forming anastomoses with other rectal arteries, specifically the middle rectal artery (a branch of the internal iliac artery) and the superior rectal artery (a continuation of the inferior mesenteric artery). These anastomoses form an important vascular network that ensures a continuous and robust blood supply to the rectum and anal canal, even if one of the main arteries is compromised.

Anatomical Relations

• Internal Pudendal Artery: The inferior rectal artery is one of the early branches of the internal pudendal artery. It shares its origin with other perineal branches and travels alongside the pudendal nerve within the pudendal canal (Alcock’s canal).
• Ischioanal Fossa: The inferior rectal artery courses through the ischioanal fossa, a wedge-shaped fat-filled space located between the ischium and the anal canal. This fossa contains fat, nerves, and blood vessels that supply the perineum and anal region.
• Levator Ani Muscle: The artery runs below the levator ani muscle, which is part of the pelvic floor and supports the rectum and anal canal. The artery is located in the fat of the ischioanal fossa, deep to this muscle.
• Anal Canal: The artery runs along the lateral walls of the anal canal, giving off branches to supply the mucosa, sphincter muscles, and surrounding tissues. The anal canal is a terminal portion of the gastrointestinal tract that plays a crucial role in continence.
• External and Internal Anal Sphincters: The artery supplies both the external anal sphincter, which is under voluntary control, and portions of the internal anal sphincter, which is involuntary. These sphincter muscles regulate the passage of feces and maintain continence.

Anastomoses

The inferior rectal artery forms several important anastomoses with other arteries that supply the anorectal region:

• Superior Rectal Artery: This artery is a continuation of the inferior mesenteric artery and supplies the upper part of the rectum. The inferior rectal artery anastomoses with the superior rectal artery in the lower rectum, forming a network that ensures a continuous blood supply.
• Middle Rectal Artery: This artery, a branch of the internal iliac artery, supplies the middle portion of the rectum. The inferior rectal artery anastomoses with the middle rectal artery, further contributing to the vascularization of the rectum and anal canal.

These anastomoses help ensure that the anorectal region receives a continuous and reliable blood supply, even if one of the main arteries is obstructed or compromised. This is particularly important in conditions such as trauma or surgery, where maintaining an adequate blood supply is essential for healing and function.

Relations with Other Structures

• Pudendal Nerve: The inferior rectal artery runs alongside the pudendal nerve, which is responsible for motor and sensory innervation to the perineal region, including the external anal sphincter. Both the artery and the nerve pass through the pudendal canal (Alcock’s canal) before branching to supply the anal and perineal regions.
• Perineal Region: The inferior rectal artery gives rise to small branches that also contribute to the blood supply of the perineum, especially the skin and soft tissues near the anal canal.

Surface Anatomy

While the inferior rectal artery itself is located deep within the ischioanal fossa and is not palpable, its proximity to the anal canal and sphincter muscles makes it an important vessel during surgical interventions or procedures involving the anorectal region. Understanding its anatomical course and branches is crucial for avoiding vascular injury during surgeries such as hemorrhoidectomy or rectal prolapse repairs.

Function

Blood Supply to the Anal Canal

The primary function of the inferior rectal artery is to provide oxygenated blood to the anal canal, ensuring the health and function of the tissues within this region. The anal canal, which is responsible for the expulsion of feces, requires a consistent blood supply to maintain its structural integrity and function. The artery supplies blood to the mucosa lining the anal canal, which is essential for maintaining the moisture and health of the tissue. Adequate blood flow supports the healing of the mucosa, particularly in conditions like hemorrhoids or anal fissures.

Blood Supply to the External and Internal Anal Sphincters

The inferior rectal artery plays a vital role in supplying the external and internal anal sphincters, which are critical for maintaining continence. The external anal sphincter is a voluntary muscle that controls the release of feces during defecation, while the internal anal sphincter is an involuntary muscle that maintains closure of the anus when at rest. Both sphincters rely on a steady supply of oxygenated blood to function properly, and the inferior rectal artery ensures that these muscles receive the necessary nutrients and oxygen for their contraction and relaxation.

Vascularization of the Perianal Skin and Tissues

The inferior rectal artery supplies blood to the perianal skin and the soft tissues surrounding the anus. These tissues are involved in maintaining the structure and health of the anal region and are subject to various stressors, including friction and pressure during bowel movements. The artery provides oxygenated blood to the epidermal and subcutaneous layers of the perianal region, supporting skin integrity and the ability to heal after minor injuries or irritation. This vascularization is crucial for maintaining the health of the perianal skin, particularly in conditions such as perianal abscesses or infections.

Contribution to Hemorrhoidal Circulation

The inferior rectal artery contributes to the blood supply of the hemorrhoidal plexus, a network of blood vessels located in the anal canal and rectum. This plexus is involved in the formation of hemorrhoids, which occur when the blood vessels become engorged and swollen. The inferior rectal artery, along with the middle rectal artery and superior rectal artery, supplies blood to the hemorrhoidal vessels. Understanding this blood supply is important in the context of hemorrhoidal disease, as the artery’s role in providing blood to this region can affect both the development and treatment of hemorrhoids.

Support for Wound Healing and Tissue Repair

The inferior rectal artery plays a crucial role in wound healing and tissue repair in the anorectal region. Injuries to the anal canal or surrounding tissues, such as anal fissures or surgical incisions (e.g., after hemorrhoidectomy or fistula repair), require a robust blood supply to heal properly. The oxygenated blood delivered by the inferior rectal artery is necessary for cell regeneration, collagen production, and the repair of damaged tissues. The artery’s function is particularly important for maintaining tissue viability and promoting recovery after injury or surgery in the anorectal region.

Collateral Circulation and Anastomosis with Other Rectal Arteries

The inferior rectal artery forms anastomoses with the middle rectal artery and superior rectal artery, ensuring that the anorectal region has a consistent blood supply, even if one of these arteries is compromised. This collateral circulation is particularly important in cases where blood flow is disrupted due to injury, surgery, or vascular disease. The anastomoses allow blood to flow through alternate routes, ensuring that the rectum, anal canal, and surrounding tissues remain well-nourished and capable of proper function. This redundancy in blood supply helps prevent tissue ischemia and promotes healing in the event of vascular damage.

Maintenance of Rectal and Anal Canal Function

The inferior rectal artery supports the overall functionality of the rectum and anal canal by supplying the necessary blood to their tissues. The smooth passage of stool through the rectum and its eventual evacuation through the anus relies on the health of the anal canal’s mucosa and sphincter muscles. The inferior rectal artery provides the blood required for the proper contraction of the sphincters, lubrication of the anal canal, and maintenance of the structural integrity of the tissues involved in defecation. Without adequate blood supply from this artery, the anal canal and sphincters would be prone to dysfunction, leading to issues such as incontinence or defecatory disorders.

Role in Supporting Perianal Nerves and Sensory Function

The perianal skin and tissues surrounding the anus are densely innervated by sensory nerves that provide feedback related to pressure, pain, and temperature. The inferior rectal artery supports these nerves by supplying blood to the perianal tissues, ensuring that the nerves remain healthy and functional. Proper blood flow to these tissues is essential for maintaining normal sensory function, which is crucial for detecting irritation, injury, or the need to defecate. Impaired blood supply to the perianal region can lead to sensory deficits, which may increase the risk of injuries going unnoticed or worsen the symptoms of conditions like anal fissures or hemorrhoids.

Removal of Metabolic Waste and CO2

In addition to delivering oxygen and nutrients, the inferior rectal artery helps in the removal of metabolic waste products, such as carbon dioxide and lactic acid, from the tissues it supplies. The sphincter muscles and the anal canal require efficient waste removal to prevent the buildup of byproducts that could lead to tissue fatigue, muscle dysfunction, or inflammation. This function is particularly important in maintaining the health and endurance of the anal sphincters, especially during periods of increased muscle activity, such as during bowel movements or when holding the sphincters closed for continence.

Support for the Pelvic Floor and Levator Ani Muscles

The inferior rectal artery runs below the levator ani muscle, which is a crucial part of the pelvic floor. While the levator ani is primarily supplied by other arteries, such as the internal pudendal artery, the inferior rectal artery contributes to the vascularization of the ischioanal fossa and the surrounding pelvic structures. By ensuring that the tissues of the perineum and anal canal remain healthy and functional, the artery indirectly supports the pelvic floor muscles, which play a key role in maintaining continence and supporting the pelvic organs.

Clinical Significance

The inferior rectal artery is clinically significant due to its role in supplying blood to the anal canal, sphincter muscles, and perianal skin. It is a key artery involved in the vascularization of the hemorrhoidal plexus, which is important in the development and treatment of hemorrhoids. During hemorrhoidectomy or other surgical procedures involving the anal region, the inferior rectal artery must be carefully managed to avoid excessive bleeding or ischemic complications.

Additionally, the artery is involved in providing blood to the external and internal anal sphincters, which are critical for maintaining continence. Disruption of the blood flow to these muscles, whether due to trauma, surgery, or vascular disease, can impair their function, leading to incontinence or defecatory disorders. Proper identification and preservation of the artery are also important during surgeries that involve the perianal or rectal region to ensure adequate blood supply and promote healing after injury or surgery.