Anal canal anatomy

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

2. 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

3. Subdivisions of the perineum
• Transverselinejoiningthe anteriorpart of ischial
tuberositiesdividesperineuminto:
1. Urogenitalregion / triangle- ANTERIORLY
2. Anal region / triangle- POSTERIORLY

4. 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

5. Learning objectives
At the end of this teachingsessionon anatomyof Anal canalall the MBBS 1st Year
studentsmust be able to correctly:
• Describethe location,extentand dimensionsof the anal canal
• Enumeratethe relations of the anal canal
• Enumeratethe subdivisionsof anal canal
• Describe& Diagrammaticallydisplaythe specialfeatureson the interior of the
anal canal
• Discussthe importanceof pectinate/ dentateline
• Write a short note on the arterial supply,venousdrainage, nervesupply &
lymphaticdrainage
• Write a short note on the sphinctersof the anal canal
• Describethe anatomicalbasisof internal & external hemorrhoids& analfistula,
anal fissure,perianal abscess
• Enumeratethe structures palpableon per rectal examination

6. Anal Canal
• Anal canalforms the lowestpart of the gastrointestinaltract
• GrossCardinalfeaturesof largeintestineabsent

7. Location & Extent of anal canal
• Situated belowlevatorani muscle
• It liesin the anal region/triangle
• From – anorectal junction to anus
• Anorectaljunction-
– 2-3 cm in front and little below tip
of coccyx
• Anus –
–Surfaceopening of canal
–4 am in front & below tip of coccyx

8. Direction & Dimensions
• Directeddownwards& backwards
• Length – 3.8-4 cm
• Closedside to side–
anteroposteriorslit

9. Anterior & posterior
Relations of anal canal in
males
Anterior & posterior
Relations of anal canal in
females
Sagittal Sections of male & female pelvis
Relations of anal canal

10. 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
Coronalsectionof pelvis& perineum

11. Interior of Anal Canal
(Subdivisions)
Subdividedinto 3 parts:
Upper part- 15mm
Middle part- 15 mm
Lower part – 8 mm

12. Upper part
• 15 mm long
• Endodermal in origin- primitive anorectalcanal
• Lining – mucus membrane
• Epithelium– simple/stratifiedcolumnar
• Colour - Plum red
• Specialfeatures –
– Anal columns
– Anal valves
– Pectinate/ dentateline
– Anal papillae

13. 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

15. Importance of pectinate line
• Divides canal into 2 parts that are different:
–In development
–In arterialsupply
–In venousdrainage
– In lymphaticdrainage
–In nervesupply

16. Middle part/ Pecten
Length -15 mm
Ectodermalorigin- proctodeum
Epithelium-stratified squamous
Bluish pinkin appearance
–Due to presenceof dense
venousplexusbetween
mucosaand musclecoat
No glands– sweat/sebaceous

17. Lower part
Length -8 mm
Ectodermalorigin-
proctodeum
Epithelium-stratified
squamouskeratinized
(true skin)
Pigmentedskin
Glandspresent– sweat/
sebaceous& hair

18. • Contrast betweenbluish pink
mucosaand blackskin
• WHITELINE OF HILTON
• At the levelof lowerend of
internalanalsphincter/
intersphinctericgroove

19. Musculature of Anal Canal
• Anal Sphincters
• Conjoint longitudnal coat
• What is the Anorectalring ?
Circular layer &
Longitudnal layer

20. Anal Sphincters
External
Internal
Thickening of circular
muscle layer

21. Anal Sphincters
Internal anal sphincter
• Smooth muscle-Thickened
circularmusclelayer
• Involuntary
• Surroundsupper 3/4th of canal
• Endsat white lineof Hilton
• Intersphinctericgroove
betweenit and subcutaneous
part of externalsphincter
External anal sphincter
• Skeletalmuscle
• Voluntary
• Surroundswhole length of
canal
• 3 parts-
– Deep
– Superficial
– Subcutaneous
Sphincters allow defecation & maintain continence

22. External Anal
Sphincter
Encircles upper end of canal –
Has no bony attachment
Encircles middle of canal – attached
to perineal body & anococcygeal
ligament
Encircles lower end of canal –
Has no bony attachment
Intersphincteric
groove
Single
Functional & Anatomic
entity

23. Conjoint Longitudnal coat
• Formed by fusion of
puborectaliswith longitudnal
muscleof rectum
• LiesbetweenInternal &
externalsphincter
• Forms a fibroelstic sheath
that breakslower down into
septain a fanwisemanner

24. Conjoint Longitudnal coat
• Laterally– most lateral forms perianal fascia
• Inferiorly– pierce subcutaneous External sphincter attached to skin – forms
corrugator cutis ani
Medially–
• Forms anal intermuscular
septum
• Some pass through
internal sphincter and
end in submucosa

25. Damage of the ring
results in
Incontinence
Anorectal ring

27. Through inferior
hypogastric plexus
Through inferior
rectal nerve

28. Clinical & surgical anatomy
• Hemorrhoids
–Internal
–External
• Anal Fissure
• Anal Fistula
• Anal / Perianalabscess

29. Hemorrhoids
• Fold of mucous membraneand submucosawith varicosed
venoustributary
INTERNAL
EXTERNAL
causedby increasedstraining or intra-
abdominalpressure(e.g., due
to constipation,pregnancyor extendedperiods of
sitting).
Patientsmay present with prolapse,
rectal bleeding, pain, and pruritus.

30. Internal Hemorrhoids
First degree
Second degree
Third degree
• Tributaries of superior rectal vein, covered by mucosa
• Protrusion from anal columns in upper half of canal
• Commoner is certain specific locations
• Sensitive only to stretch so may cause non specific aching pain/ painless

31. PRIMARY PILES
– Enlargement of 3 main radicles of superior rectal veins in anal
columns
– usually occur at 3(left lateral), 7 (right posterior) & 11 o clock (right
anterior) position
SECONDARY PILES- any other location

32. External hemorrhoids
• Tributaries of inferior rectal vein
• At the anal margin
• Covered by skin
• Painful

33. Anatomical basis of engorgement of anal
cushions
• Pressureoverveinsat siteswherethey piercethe muscular
coat, during musclecontraction
• Increasedportal pressureis directlytransmitted at
portosystemiccommunicationsdue to absenceof valves
• Loose connectivetissuearound veinsforms a poor support
• Excessivestrainingassociatedwith chronicconstipation
• Somemay havecongenitalweaknessin vein walls

34. Anal Fissure
• Elongated ulcer in mucosa due to tearing of anal valves
• In people suffering from chronic constipation
• Extremely painful (lower part of canal)
• Mostly posterior midline, may occur in anterior midline ( superficial
external sphincter does not encircle anteriorly & posteriorly)

35. Anal Abscess
• Due to fecal trauma to anal
mucosa
– Infectionin submucosafollowing
fissure
– Complicationof fissure
– Infectedanal mucosalglands
• On the basis of location
– Submucosalabscess
– Subcutaneousabscess
– Ischiorectalabscess
– Pelvirectalabscess
is a painful condition in which a collection of pus
develops near the anus.
This often appears as a painful boil-like swelling
near the anus. It may be red in color and warm to the
touch.
Anal abscesses located in deeper tissue are less
common and may be less visible.

36. Anal Fistula
CAUSE:
– Due to spread of infection
from anal abscess
– Due to improper treatment of
anal abscess
• Abscessopens at two
places
– In the lumen of anal canal or
lower rectum
– On the skin of perianal
region
An anal fistula is a small tunnel that develops
between the end of the bowel and the skin
near the anus

37. Digital Rectal Examination-by gloved index finger
• Anteriorly:
– Opposite Terminal phalanx
• In males- rectovesicalpouch,posterior
surfaceof bladder, seminal vesicles,vas deferens
• In females – rectouterinepouch, vagina,cervix
– Opposite Middle phalanx
• In males – prostate
• In females – vagina
– Opposite Proximal phalanx
• In males- perinealbody, bulb of penis
• In females– perinealbody, lower vagina