Lecture notes for medical students

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7. See notes for bibliography.

2. Anal Canal

3. Anal Canal
• Most distal portion of the alimentary canal.
• Extends for a distance of about 3 cm from
the anorectal ring to the hairy skin of the
anal verge.

4. Features
Anterior wall shorter than posterior wall
Surrounded by sphincter ani muscles
Canal closed except during defaecation
Measurements
Length (adult) 3.8 cms
Breadth when empty
lateral walls approximated
(antero-posterior slit)

5. RELATIONS
In front:
1. Perineal body
2. In male – bulb of penis & spongy urethra
In female – Lower part of post. wall of vagina
Behind:
Ano-coccygeal raphe
Fibro-fatty tissue bet’ peri-anal skin & raphe
On each side:
Ischio-rectal fossa and its contents

6. INTERIOR OF ANAL CANAL

7. INTERIOR OF ANAL CANAL
Divided by pectineal line & Hilton’s line into 3 areas
1. Upper (15 mm)
2. Intermediate (15 mm)
3. Lower (8 mm)
(Anal verge)
Pectinate / dentate line
Hilton’s line

9. PECTINATE LINE
Muco-cutaneous junction of anal canal
Corresponds with position of anal valves
Situated at the middle of internal sphincter
Divides anal canal into upper and lower areas (proctodeum)
which are different in development, blood supply, lymph
drainage and in nerve supply

10. Distinction Above Pectinate line Below Pectinate line
Destination of
lymph
drainage
Internal iliac lymph nodes
(pararectal lymph nodes)
Superficial inguinal lymph nodes
(Below Hilton’s line)
Epithelium Columnar epithelium Stratified squamous epithelium ,
non keratinized
Embryologica
l origin
Endoderm Ecotoderm
Artery Superior rectal artery> Inf.
Meseteric
Middle & inferior rectal arteries>
Internal iliac
Vein Superior rectal vein> Inf.
Meseteric
Middle & inferior rectal veins>
Internal iliac
Hemorrhoids
classification
Internal hemorrhoids (not
painful)
External hemorrhoids (painful)
Nerves Inferior hypogastric plexus
Symp L1,L2 & parasymp
S2,S3,S4
Inferior rectal nerves > pudendal
nerve

11. HILTON’S LINE
It is a color contrast bet’ bluish pink area above and
black skin below
The line is represented by inter-sphincteric groove at
the lower end of the internal sphincter
Indicates lower end of internal sphincter
Anal intermuscular septum is attached carrying the fibres
of levator ani and longitudinal muscle of rectum
Ischiorectal abscess when communicates with anal canal
usually opens at or below Hilton’s line

12. ANAL GLANDS
Floor of the sinus receives the ducts of the tubular anal glands,
which ramify in the sub-mucous coat of the anal canal and sometimes
penetrate the internal sphincter muscle. These glands are occasionally
Infected and act as a source of anal fistula.

13. ANAL CANAL
• Two – Internal & external, surround the
anal canal.

14. – Extension of levator ani around anorectum
– Voluntary sphincter
– Supplied by pudendal nerver
– 3 compnents :
• Subcutaneous
• Superficial
• Deep

15. INTERNAL SPHINCTER

16. INTERNAL SPHINCTER
Involuntary sphincter
Thickening of circular muscle of lower part of rectum
Surrounds upper 3/4th of anal canal
Lower end corresponds with Hilton’s line
Middle corresponds with pectinate line
Nerve supply: Sup.Hypogastric & pelvic splanchnic

18. Blood supply

19. Blood supply
• Arterial supply:
– Superior rectal artery > Inf. Mesenteric
– The middle rectal arteries arise from the
internal iliac arteries.
– The inferior rectal arteries, branches from the
internal pudendal arteries.
• Venous drainage :
– Above dentate line : Int. hem. plexus sup
rectal vein  Inf. Mesenteric vein
– Below dentate line : Ext. hem. Plexus
Middle rectal vein Int. iliac vein OR
Inf. Rectal vein  pudendal vein  Int. iliac vein

20. Nerve supply

21. Nerve supply
• Below the dentate line, cutaneous
sensations conveyed by afferent fibers in
the inferior rectal nerves.
• Above the dentate line : parasympathetic
fibres

22. PR - Per rectal examination

23. Proctoscopy

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