The anal canal is located below the pelvic diaphragm and extends from the anorectal junction to the anus. It is surrounded by inner involuntary and outer voluntary sphincter muscles and is around 3.8 cm long. The anal canal has three parts - the upper mucous part lined by columnar epithelium, the middle transitional zone, and the lower cutaneous part lined by skin. It receives blood supply from the inferior and superior rectal arteries and drains into internal iliac and inguinal lymph nodes. Nerve supply includes autonomic nerves above the pectinate line and somatic nerves below.

1. Anal Canal
- Aditi Lahane

2. Introduction
 Terminal part of GIT
 Location - Below the level of pelvic diaphragm
 Sacuulations and Taeniae - Absent

3. Length , Extent and Directions
 3.8 cm long
 Extension - From Anorectal Junction to the Anus
 Surrounded by inner involuntary and outer voluntary
sphincters
 Anorectal Junction - Forward convexity of perineal
flexure of rectum
 Anus - Surface opening - 4 cm below and infront of the
tip of the coccyx in the cleft between two buttocks
 Surrounding skin is pigmented and contains a large
number of apocrine glands

4. Relations of the Anal Canal
Anteriorly
 In both sexes - Perineal
body
 In Males -
Membranous urethra
and bulb of Penis
 In Female - Lower end
of Vagina
Posteriorly
 Anococcygeal ligament
 Tip of the coccyx
 Laterally - Ischioanal
Fossa
 All round -Surrounded
by sphincter muscles

5. Interior of Anal Canal
Divided into 3 parts -
• Upper Mucous Part
• Middle Part / Transistional Zone / Pecten
• Lower Cutaneous Part

6. Interior of Anal Canal
• 15 mm long
• Lined by Mucous Membrane
• Endodermal in origin
Mucous Membrane
√ 6 - 10 vertical columns / folds ~ Anal Columns /
Morgagni
√ Lower ends of anal columns are united to each other
by short trasverse folds of mucous membrane ~ Anal
Valves
√ Above each Valve - Depression in mucosa ~ Anal Sinus

7. √ Anal Valves - Together - Trasverse Line - Runs all round
the anal canal ~ Pectinate / Dentate Line
|
Situated opposite to middle of
intetnal Anal Sphincter - The junction of ectodermal and
endodermal parts
√ Anal Valves ocaasionally show Epithelial Projections -
Anal Papillae
√ Anal sinuses contain Anal Glands

8. Middle Part / Transitional Zone /
Pecten
 15 mm
 Also lined by Mucous Membrane but anal columns are absent
here
 Mucosa has Bluish appearance - dense venous plexus - Lies
between it and muscle coat
 Mucosa - Less mobile
 White line of Hilton
 At the level of interval between the subcutaneous part of EAS
and the lower border of IAS
 Marks the lower limit of pecten / stratified sqamous
epithelium - thin , pale and glossy , devoid of sweat glands

9. Lower Cutaneous Part
 8 mm long , lined by true skin , contaning
sabceous glands
 Epithelium of lowest part resembles that of
pigmented skin - Sabaceous glands , sweat glands
and hair

11. Musculature of Anal Canal
Anal Sphincters
1. Internal Anal Sphincter
2. External Anal Sphincter

12. 1. Internal Anal Sphincter
 Involuntary
 Formed by thickned circular muscle coat
 Surrounds the upper 3/4 ths - 30 mm of the anal
canal to the white line of Hilton

13. 2 . External Anal Sphincter
 Voluntary
 Made up of striated muscles
 Surrounds the whole length of the anal canal
 3 parts - Subcutaneous , Superficial and Deep

15. Conjoint Longitudinal Coat
√ Formed by the fusion of the
Puborectalis and Longitudinal
muscle coat of rectum
√ Lies between external and
internal sphincters

17. Anorectal Ring
 Muscular ring
 At the Anorectal Junction
 Formation - Puborectalis ,uppermost fibers
of EAS and the internal sphincter

19. Surgical Spaces Related to Anal
Canal
 Ischioanal Space - Lies on each side of the anal canal
 Perineal Space - Surrounds the anal canal below the
white line - Contains - Lower fibers of EAS , External
rectal venous plexus ,terminal branches of the inferior
rectal venous vesseles and nerves
 Submucous Space -Lies above the white line between
the mucuous membrane and intetnal sphincter -
Contain - Internal rectal venous plexus , Lymphatics

20. Arterial Supply
 Above the Pectinate Line -
Superior Rectal Artery
 Below the Pectinate Line - Inferior
Rectal Artery

22. Venous Drainage
 Internal rectal venous plexus / Haemorrhoidal plexus
- Submucosa of the anal canal- Drains mainly into
superior rectal vein
 External rectal plexus - Outside the muscular coat of
rectum and anal canal - lower part - drained by the
inferior rectal vein into internal pudendal vein
 Anal veins - Arranged radially around the anal margin

25. Lymphatic Drainage
 Part above the Pectinate Line - Drain with
those of the rectum into internal iliac
nodes
 Vesseles from part below the
PectinateLine - Drain into medial group of
superficial inguinal nodes

27. Nerve Supply
 Above the Pectinate Line - Autonomic
Nerves - both sympathetic and
parasympathetic
 Below the Pectinate Line - Somatic Nerves
 Sphinctes - Cotraction - Sympathetic
Nerves , Relaxation - Parasympathetic
Nerves , External sphincter - inferior rectal
nerve and by the perineal branch of 4 th
sacral nerve

28. Histology
 Upper 15 mm - Simple / Stratified Columnar
 Middle 15 mm - Stratified Squamous
without any sweat / sabaceous glands / hair
follicles
 Lowest 8 mm - Resembles true skin with
sweat / sabaceous glands and hair follicles

29. Development
 Upper 15 mm - Primitive anorectal
canal
 Lower 8 mm - Ectodermal
invagination i.e. Proctodeum

30. Clinical Anatomy
 Piles / Haemorrhoids
 Fistula / Fissure in Ano
 Anal Stenosis
 Anal Agencies with or without Fistula