HEMORRHOID DISEASE: DIAGNOSIS TREATMENT AND COMPLICATION MANAGEMENT

Hemorrhoidal_Disease_Bahadir_Egekapak

ANAL CANAL ANATOMY

Ahmet Atasever

Demiroğlu Science University, Faculty of Medicine, Department of General Surgery, İstanbul, Türkiye

Atasever A. Anal Canal Anatomy. In: Ege B, editor. Hemorrhoidal Disease: Diagnosis, Treatment and Complication Management. 1st ed. Ankara: Türkiye Klinikleri; 2025. p.15-21.

ABSTRACT

The anal canal is a critical anatomical structure that serves as the terminal portion of the gastrointestinal tract, facilitating the transition from the rectum to the external environment. Its distinctive structure and functionality are crucial for maintaining continence and facilitating defecation, making it a key focus of both anatomical and clinical studies. The anal canal is anatomically divided into superior and inferior segments by the pectinate (dentate) line, a key landmark that separates the endodermal and ectodermal embryological origins. This division also dictates differences in arterial supply, venous drainage, lymphatic pathways, and neural innervation. The superior segment is supplied by the superior rectal artery, connects to the portal venous system, and is regulated through autonomic innervation. In contrast, the inferior segment is supplied by the inferior rectal artery, drains into the systemic venous circulation, and is innervated by somatic nerves.

Microscopically, the anal canal is composed of three distinct epithelial zones: the columnar zone, transitional zone, and squamous zone. These zones exhibit structural and functional variations that have implications for pathological conditions. For instance, the columnar zone, with its longitudinal mucosal folds (columns of Morgagni), is prone to conditions such as perianal abscesses when anal crypts become blocked. The transitional zone marks the transition between simple columnar and stratified squamous epithelium, while the squamous zone, located below the dentate line, transitions from non-keratinized to keratinized epithelium near the anal verge.

The anal canal’s anatomical relationships are equally significant. Anteriorly, it is anatomically adjacent to the perineal body and structures like the membranous urethra and bulb of the penis in males, as well as the lower third of the vagina in females. Posteriorly, the coccyx and anococcygeal ligament provide support, while laterally, the ischioanal fossae, filled with fat and traversed by the pudendal canal, flank the canal.

This intricate anatomy underpins the anal canal’s physiological roles and its involvement in various disorders, including hemorrhoids, anal fissures, chronic constipation, and anorectal dysfunctions. Thorough knowledge of its structure and function is crucial for accurately diagnosing and managing these conditions, emphasizing its significance in both surgical and clinical practice.

Keywords: Anal canal; Anus diseases; Anatomy; Hemorrhoids; Rectum

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