Anal canal anatomy

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