Anal canal and rectum: structure, function and common diseases

Structure and function of the anal canal

The anal canal is an important part of the human digestive system. It begins at the anal verge and ends at the anorectal junction, also known as the linea pectinea, mucocutaneous junction or linea dentata. There are 8-12 anal crypts and 5-8 papillae in this area. The anal canal is lined with anoderm, which is a continuation of the outer skin. This region is very sensitive as it is innervated by somatic sensory nerves that react to pain stimuli.

Venous and lymphatic drainage

Venous drainage from the anal canal is into the cavernous system, while the anorectal junction can drain into both the portal and cavernous systems. The lymphatic vessels from the anal canal lead to the internal iliac lymph nodes, the posterior vaginal wall and the inguinal nodes. This venous and lymphatic drainage is crucial as it determines the spread of malignant tumors and infections.

Structure and function of the rectum

The rectum is the continuation of the sigmoid and begins at the level of the 3rd sacral vertebra. It extends to the anorectal junction. The lining of the rectum consists of a shiny red, glandular mucous membrane that is supplied by autonomic nerves and is therefore relatively insensitive to pain. The venous drainage of the rectum is via the portal vein system, while the lymphatic return flow is along the upper hemorrhoidal vascular pedicle to the lower mesenteric and aortic lymph nodes.

Sphincter ring and its significance

The sphincter ring that surrounds the anal canal consists of an internal sphincter, the central portion of the levators and parts of the external sphincter. The anterior part of the sphincter is particularly susceptible to injury, which can lead to incontinence. The puborectalis muscle forms a muscular sling around the rectum and supports the process of micturition and defecation.

Common anorectal diseases

The most common anorectal diseases include

• Anal cancer
• Anal fissure
• Anal itching
• Anorectal abscess
• Anorectal fistula
• Fecal incontinence
• Hemorrhoids
• Levator syndrome
• Pilonidal disease
• Proctitis
• Foreign bodies in the rectum
• Obstructive defecation syndrome (ODS)
• Rectal prolapse
• Rectal carcinoma
• Colorectal carcinoma
• Solitary rectal ulcer syndrome

These conditions can cause various symptoms and complaints and require specialized diagnosis and treatment. Our practice offers comprehensive examinations and individualized therapies for all of the above conditions. Contact us for a consultation or to make an appointment.