Anatomy of Anal Canal || Boundaries, Specific Features, Blood & Nerve Supply, Lymphatic Drainage скачать в хорошем качестве

Anatomy of Anal Canal || Boundaries, Specific Features, Blood & Nerve Supply, Lymphatic Drainage

The anal canal is the terminal part of the lower gastrointestinal tract, measuring about 3 to 4 cm in length, extending from the anorectal junction to the anus. It lies extraperitoneally and is surrounded by two sphincters—the internal anal sphincter (involuntary) and the external anal sphincter (voluntary)—which maintain fecal continence and control defecation. Its anatomy is divided mainly by the pectinate (dentate) line into two regions with distinct features, blood supplies, nerve supplies, and lymphatic drainage. Boundaries Superior boundary: Anorectal junction, where the rectum transitions into the anal canal. Inferior boundary: The anal verge or anus, the external opening. The anal canal lies within the anal triangle of the perineum, below the pelvic diaphragm. Specific Features The anal canal is divided into three zones: *Columnar (colorectal) zone:* Upper two-thirds above the pectinate line, lined by simple columnar epithelium. It contains longitudinal mucosal folds called anal columns with anal valves connecting their lower ends, forming the pectinate line. Anal sinuses beneath the valves harbor anal glands. *Intermediate zone (anoderm):* About 1 cm distal to the pectinate line, lined by non-keratinized stratified squamous epithelium. *Cutaneous (squamous) zone:* Distal third lined with keratinized stratified squamous epithelium continuous with surrounding perianal skin. The pectinate line is a critical landmark where embryological origins, histology, neurovascular supply, and lymphatic drainage differ. Blood Supply Above the pectinate line (upper 2/3): Supplied by the **superior rectal artery**, a branch of the inferior mesenteric artery. Below the pectinate line (lower 1/3): Supplied by the *middle rectal artery* (from internal iliac artery) and *inferior rectal artery* (from internal pudendal artery). Venous Drainage Superior to the pectinate line: Drains into the superior rectal vein, which drains into the portal venous system via the inferior mesenteric vein. Inferior to the pectinate line: Drains via the middle and inferior rectal veins into the systemic circulation via internal iliac veins. Nerve Supply Above the pectinate line: Visceral innervation via the inferior mesenteric plexus, pelvic splanchnic nerves, and inferior hypogastric plexus, providing autonomic control. Below the pectinate line: Somatic innervation via the **pudendal nerve**, making this area sensitive to pain, temperature, and touch. Lymphatic Drainage Above the pectinate line: Lymph drains to the **internal iliac and inferior mesenteric lymph nodes**. Below the pectinate line: Lymph drains to the **superficial inguinal lymph nodes**. This detailed anatomical division of the anal canal facilitates distinct functional roles and clinical implications, especially in surgery and disease management such as in hemorrhoids, fissures, and cancers.[3][4][5] [1](https://teachmeanatomy.info/abdomen/g...) [2](https://emedicine.medscape.com/articl...) [3](https://www.kenhub.com/en/library/ana...) [4](https://www.ncbi.nlm.nih.gov/books/NB...) [5](https://en.wikipedia.org/wiki/Anal_canal) [6](https://www.slideshare.net/slideshow/...) [7](https://my.clevelandclinic.org/health...) [8](   • Anal Canal - Simplified Anatomy + Anki fla...  ) [9](https://www.sciencedirect.com/topics/...) [10](   • Anal Canal - 3 | Blood supply and Nerve Su...  ) [11](https://teachmeanatomy.info/abdomen/g...) [12](https://www.earthslab.com/anatomy/ana...) [13](https://www.pathologyoutlines.com/top...)