Anatomy of the Anal Canal: Structure, Subdivisions, and Clinical Significance, Study notes of Anatomy

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Anatomy of Anal

Canal

Dr Garima Sehgal Associate Professor Department of Anatomy King George’s Medical University, UP, Lucknow

DISCLAIMER:

• The presentation includes images which are either hand drawn or have been taken from google images or books.
• They are being used in the presentation only for educational purpose.
• The author of the presentation claims no personal ownership over images taken from books or google images.
• However, the hand drawn images are the creation of the author of the presentation

Anal canal may be affected by many conditions that are not so rare, not necessarily serious and endangering to life but on the contrary very INCAPACITATING Haemorrhoids

Anal fistula

Anal fissure Perianal abscess

Learning objectives

At the end of this teaching session on anatomy of Anal canal all the MBBS 1 st Year students must be able to correctly:

• Describe the location, extent and dimensions of the anal canal
• Enumerate the relations of the anal canal
• Enumerate the subdivisions of anal canal
• Describe & Diagrammatically display the special features on the interior of the anal canal
• Discuss the importance of pectinate / dentate line
• Write a short note on the arterial supply, venous drainage, nerve supply & lymphatic drainage
• Write a short note on the sphincters of the anal canal
• Describe the anatomical basis of internal & external hemorrhoids & anal fistula, anal fissure, perianal abscess
• Enumerate the structures palpable on per rectal examination

Location & Extent of anal canal

• Situated below levator ani muscle
• It lies in the anal region/ triangle
• From – anorectal junction to anus
• Anorectal junction-
  • 2 - 3 cm in front and little below tip of coccyx
• Anus –
  • Surface opening of canal
  • 4 am in front & below tip of coccyx

Direction & Dimensions

• Directed downwards & backwards
• Length – 3.8- 4 cm
• Closed side to side – anteroposterior slit

Relations of anal canal

ANTERIORLY- Perineal body & In Males- membranous urethra & bulb of penis In Females – Lower part of vagina POSTERIORLY – Anococcygeal ligament Tip of coccyx LATERALLY – Ischioanal fossa ALL AROUND – Sphincter muscles Coronal section of pelvis & perineum

Interior of Anal Canal (Subdivisions) Subdivided into 3 parts: Upper part- 15mm Middle part- 15 mm Lower part – 8 mm

Special features of upper part

ANAL COLUMNS

• 6 - 10 vertical mucosal ridges
• Permanent mucosal folds
• Contain radicals of superior rectal vein ANAL VALVES
• Semilunar mucosal folds uniting lower end of anal column
• Form – PECTINATE LINE ANAL SINUS
• Depression above anal valve
• Floor contains openings of anal glands

Middle part/ Pecten Length - 15 mm Ectodermal origin- proctodeum Epithelium- stratified squamous Bluish pink in appearance

• Due to presence of dense venous plexus between mucosa and muscle coat No glands – sweat/ sebaceous

Lower part Length - 8 mm Ectodermal origin- proctodeum Epithelium- stratified squamous keratinized (true skin) Pigmented skin Glands present – sweat/ sebaceous & hair

Musculature of Anal Canal

• Anal Sphincters
• Conjoint longitudnal coat
• What is the Anorectal ring? Circular layer & Longitudnal layer

Anal Sphincters

External Internal Thickening of circular muscle layer