Anal Canal and lower than irukkum

1. Chapter 36
Anal Canal
Textbook of
Human Anatomy
Volume 4: Abdomen and Pelvis
Author: Dr Yogesh Sontakke,
JIPMER, Pondicherry
©CBS Publishers & Distributors Pvt Ltd, New Delhi

2. As per:
Competency based Undergraduate curriculum
AN49.5
• Explain anatomical basis of perineal tear, episiotomy, perianal
abscess, and anal fissure
• This chapter contains anatomy of perianal abscess and anal
fissure
Medical Council of India, Competency based Undergraduate curriculum for the Indian Medical Graduate, 2018. Vol. 1; pg 1-80.
Human Anatomy/Yogesh Sontakke
2

3. • Terminal part of gastrointestinal tract
Location
• Located in perineum below pelvic diaphragm
• Located in anal triangle between right and left ischioanal fossae

4. Some Interesting Facts
• Fat-filled ischioanal fossae allow expansion of anal canal during
defecation
• Three cardinal features of large intestine (sacculations, taenia
coli, and appendices epiploicae) are absent in anal canal

5. Extent and Course
• Length: 3.8 cm
• Breath: When empty, lateral walls of anal canal – approximated, and
anal canal appears as slit
• Extent: Anal canal extends from anorectal junction to anal orifice
• Anorectal junction: Marked by formal convexity of perineal flexure of
rectum
• Lies 2–3 cm in front and slightly below tip of coccyx

6. Extent and Course
• Anus: External opening of anal canal
• Situated about 4 cm below and in front of tip of coccyx in natal
cleft (cleft between buttocks)
• Direction: Directed downward and backward

7. Relations
Anterior
• Perineal body
• In males: Membranous urethra and bulb of penis
• In females: Lower part of the vagina
• Posterior
• Anococcygeal raphe
• Tip of coccyx
• Fibrofatty tissue
Lateral (on each side)
• Ischioanal fossa and contents

8. Interior of Anal Canal
• For surgical description, interior of anal canal – divided into three
parts: Upper, middle, and lower by pectinate line and Hilton’s line
• Upper part has different development, blood supply, lymphatic
drainage, and nerve supply than parts of anal canal below
pectinate line (middle and lower parts)

9. Difference between upper and lower parts of anal canal
Feature Upper part of anal canal (above pectinate
line)
Lower part of anal canal (below
pectinate line)
Development Endoderm of hindgut
Lining epithelium Simple columnar epithelium Stratified squamous epithelium
Arterial supply Superior rectal artery Inferior rectal artery
Venous
drainage
Superior rectal vein drains into portal vein Inferior rectal vein drains into
systematic vein
Lymphatic
drainage
Internal iliac nodes Superficial inguinal nodes
Nerve supply Autonomic nerves Somatic nerve (inferior rectal)
Sensation Sensitive to ischemia, distension, spasm Pain, touch, temperature, pressure
Hemorrhoidal
piles
Internal painless piles External painful piles

10. • About 15 mm long and lies above pectinate line
• Has following features
• Anal columns of Morgagni: Permanent
longitudinal mucosal folds
• Are 6–10 in number
• Anal columns contain terminal branch of
superior rectal artery and vein
Features of upper part (above pectinate line)

11. • Anal valves (valves of Ball): Are crescentic
mucous folds connecting lower ends of anal
columns
• These anal valves have free margin, and upper
and lower surfaces
• Pectinate line or dentate line: Free margin of anal
valve forms line called pectinate or dentate line
Features of upper part (above pectinate line)

12. • Anal sinuses: Are depressions (recesses) above
anal valves
• Ducts of submucosal tubular anal glands open in
floor of anal sinuses
Features of upper part (above pectinate line)

13. • Anal papillae: Are occasional epithelial projections
from free margin anal valves
• Anal papillae represent remnant of embryonic anal
membrane
• Anal glands: Are tubular submucosal glands
• Their ducts open in floor of anal sinuses
• Note: Upper part of anal canal (above pectinate line)
– endodermal in origin and lined by simple columnar
epithelium
Features of upper part (above pectinate line)

14. • About 15 mm long
• Called transition zone or area of pecten
• Lined by non-keratinized stratified
squamous epithelium without sebaceous
and sweat glands
• Color: Middle part of anal canal – bluish
because of dense venous plexus lies
deep to mucosa
Features of middle part

15. • White line of Hilton: Separates middle
and lower part of anal canal
• Demarcates bluish pink area above and
black skin below
• Lies at lower end of internal anal
sphincter as inter-sphincteric groove of
anal canal
Features of middle part

16. Lower cutaneous part
• About 8 mm long and lined by skin
shows sebaceous and sweat glands,
hairs, and pigmented
Features of middle part

17. Pectinate line
Q. Define pectinate line and significance
• Represents free margin of anal valves
• Separates upper and middle parts of anal canal
Significance of pectinate line
• Development: Part of anal canal above pectinate line develops from
endodermal cloaca and below develops from ectodermal proctodeum

18. Pectinate line
Q. Define pectinate line and significance
• Arterial supply: Area above pectinate line – supplied by superior rectal
artery and below by inferior rectal artery
• Venous drainage: Area above pectinate line – drained by superior
rectal vein and below by inferior rectal vein into systematic veins

19. Pectinate line
• Lymphatic drainage: Area above pectinate line – drained into
internal iliac nodes and below into superficial inguinal nodes.
Hence, pectinate line – called watershed line
• Nerve supply: Area above pectinate line – supplied by
autonomic nerves and below by somatic (spinal) nerves
• Pain sensation: Area above pectinate line – pain insensitive,
whereas below pain sensitive

20. Musculature of Anal Canal
• Has powerful sphincters
• Anal sphincters – divided into external and internal anal sphincters
Internal anal sphincter
• Involuntary in nature
• Formed by thickening of circular muscle coat of anal canal
• Surrounds upper 3/4ths of anal canal (up to Hilton’s line)

21. Some Interesting Facts
• Hilton’s line indicates lower end of internal anal sphincter muscle
• Hilton’s line marks lower limit of pecten
• Here, anal intermuscular septum – attached carrying fibers of
levator ani and longitudinal muscle of rectum
• Anal fascia and lunate facia extend up to Hilton’s line

22. Some Interesting Facts
• Hilton’s line demarcates mucocutaneous junction
• Internal anal sphincter – surrounded by superficial and deep parts
of external anal sphincter
• Internal venous plexus lies between mucosa and internal anal
sphincter of anal canal

23. External anal sphincter
• Voluntary in nature
• Surrounds entire length of anal canal
• Consists of three parts: Deep, superficial, and subcutaneous
• Deep part: Annual in shape and surrounds anorectal junction
• Does not have bony attachment
• Inserted into perineal body
• Superficial part: Elliptical in shape
• Arises from tip of coccyx and anococcygeal raphe posteriorly

24. External anal sphincter
Superficial part
• Surrounds lower part of internal anal sphincter and inserts into
perineal body in front
• Subcutaneous part: Has flattened band around anus
• Lies below internal anal sphincter
• Has no bony attachments
• Traversed by fibroelastic septa derived from conjoint longitudinal
muscle coat of anal canal

27. Some Interesting Facts
• External anal sphincter contains type I slow twitch fibers –
adapted for prolonged contraction
Recent concept
• External anal sphincter does not have three parts
• has deep and lower parts
• Upper part – attached to anococcygeal ligament posteriorly and
perineal body anteriorly

28. Some Interesting Facts
Recent concept
• Upper most fibers blend with puborectalis and attach to
anococcygeal raphe posteriorly and transverse perineal muscles
anteriorly
• Lower fibers of external anal sphincter lies inferior to the internal
anal sphincter and traversed by fibers of conjoint longitudinal
muscle

29. Some Interesting Facts
• Conjoint longitudinal muscle coat: Formed by fusion of puboanalis and
longitudinal muscle coat of rectum
• At anorectal junction, lies between external and internal anal sphincters
• Lower portion (below the Hilton’s line) forms diverging fibroelastic septa that
fan-out through subcutaneous part of external anal sphincter
• These fibroelastic septa – attached to skin around anus and form
corrugator cutis ani
• Perianal fascia – derived from lateral most septa
• Anal intermuscular septum – medial most fibroelastic septum

30. Some Interesting Facts
• Anorectal ring: Muscular ring present at anorectal junction
• Formed by fusion of puboanalis, uppermost fibers of external anal
sphincter, and internal sphincters
• Rectal examination: Digital examination of rectum and anal canal
– called per rectal examination
• Anorectal ring can be easily felt by finger in anal canal
• Surgical division of anorectal ring results in rectal incontinence

31. Surgical Spaces Related to Anal Canal
• Spaces containing fat surrounding anal canal
• These spaces include two ischioanal fossae, perianal space, and
subcutaneous space of anal canal
• Ischioanal fossae lie on each side of anal canal and filled with fat
• Perianal space surrounds anal canal below Hilton’s line
• Lies between perianal fascia and skin

32. Blood Supply, Lymphatic Drainage, and Innervation
Arterial supply
• Part of anal canal above pectinate line – supplied by superior rectal artery
• Part of anal canal below pectinate line – supplied by inferior rectal artery
Venous drainage
• Part of anal canal above pectinate line – drained into portal venous system
by superior rectal veins.
• Part of anal canal below pectinate line – drained into systemic veins by
inferior rectal veins

33. Some Interesting Facts
• Internal rectal venous plexus or hemorrhoidal plexus lies in the
submucosa of anal canal
• Site for portal and systemic venous communication
• This plexus – in form of series of dilated pouches connected by
transverse branches around anal canal
• Venous pouches located in three anal columns (lie at 3, 7, and 11
o’clock locations on lithotomy position) – large and potential sites for
primary internal piles
• External rectal venous plexus lies outside muscle coat of rectum and
anal canal

34. Some Interesting Facts
• Drained by superior rectal vein into inferior mesenteric vein,
middle rectal vein into internal iliac vein, and inferior rectal vein
into internal pudendal vein
• Anal veins – arranged radially around anal margin
• Excessive straining during defecation may rupture anal veins and
form subcutaneous perianal hematoma called external piles

35. Lymphatic drainage
• Part of anal canal above pectinate line drains into internal iliac
nodes
• Part of anal canal below pectinate line drains into superficial
inguinal nodes
• Thus, pectinate line forms watershed line of anal canal

36. Innervation
• Above pectinate line anal canal – supplied by following autonomic
nerves
• Sympathetic by inferior hypogastric plexus (L1, L2)
• Parasympathetic by pelvic splanchnic nerves (S2, S3, S4)
• This area – insensitive to cutaneous sensation
• Below pectinate line, anal canal – supplied by inferior rectal (S2,
S3, S4) nerve

37. Innervation
Sphincters
• Internal sphincter – involuntary and contracted by sympathetic
fibers but relaxed by parasympathetic fibers
• – External sphincter – voluntary and supplied by inferior rectal
nerve and perianal branch of 4th sacral nerve

38. Development of Anal Canal
• Upper part of anal canal – derived from endoderm of primitive
anorectal canal
• Lower part of anal canal – derived from ectoderm of proctodeum
• Anal membrane ruptures at birth and forms communications of gut to
exterior
• Remnants of anal membrane forms anal valves
• Non-continuity of the anal canal to exterior – imperforate anus

39. Q. Write short note on hemorrhoids
or piles
• Definition: Hemorrhoids or piles
are dilated veins in lower part of
anal canal
Hemorrhoids (piles)

40. Types
• According to locations, hemorrhoids –
classified as internal or true piles and
external or false piles
• Internal or true piles: These are
saccular dilatations of internal rectal
venous plexus
• They occur above pectinate line;
hence, they are painless
Hemorrhoids (piles)

41. Types
• During strenuous defecation, internal
piles may rupture and bleed profusely
• Internal hemorrhoids may be primary
or secondary
• Primary piles are formed due to
dilatation of tributaries of superior
rectal vein lies in anal columns
Hemorrhoids (piles)

42. Types
• Locations of primary piles correspond
to 3, 7, and 11 o’clock positions of
anal wall, when viewing interior of anal
canal in lithotomy position
• Varicosities in other positions called
secondary piles
Hemorrhoids (piles)

43. Types
• Structure of pile: Anatomically
each pile consists of fold of
mucosa and submucosa
containing dilated tributary
(radicle) of superior rectal vein
with branch of superior rectal
artery
Hemorrhoids (piles)

44. • External (false) piles: Dilatations of
tributaries of inferior rectal vein occur
below pectinate line, hence – painful
• They do not bleed on strenuous
defecation
• They form thrombosed small tense
hematoma due to rupture of
subcutaneous vein
• Hence, external piles are also termed
perineal hematoma
Hemorrhoids (piles)

45. • Piles (hemorrhoids): These are variceal dilatation of
submucosal anal and perianal venous plexuses
Clinical Integration

46. Fistula in ano
• Fistula in anal canal
• Abnormal tract connecting cavity of
abscess to interior of anal canal or with
exterior on skin
• Caused by spontaneous rupture of
abscess around anus
• Low-level anal fistula passing through
lower part of superficial anal sphincter –
most common fistula in ano
Clinical Integration

47. Fissure in ano
• Fissure caused by rupture of any
one of anal valves of Morgagni
by passage of hard fecal mass
• Anal fissures occur commonly in
midline posteriorly
• As anal valves on inferior aspect
are supplied by somatic (inferior
rectal) nerve, anal fissures are
painful
Clinical Integration

48. Clinical Integration
• Factors responsible for internal piles
• Poor support to veins from surrounding loose connective tissue
• Absence of valves in superior rectal and portal veins
• Chances of portal hypertension
• Compression of veins at site of exit from muscular rectal wall
• Constipation prolonged standing; excessive straining at stool

49. Thank you…