APPLIED ANATOMY OF THE ANAL CANAL

Definition

Surgical :

The anal canal is the terminal portion of the intestinal tract it begins at the anorectal junction (the point passing through the levator ani muscles), is about 4 cm long, and terminates at the anal verge.

Anatomical :

that extends from the dentate line to the anal verge.

Anteriorly

Male : bulb of urethra Female : perineal body and vagina

Posteriorly : Coccyx and puborectalis muscle

Laterally Ischio rectal fossa containing inferior

hemorrhoidal vessels and pudendal nerve

Surrounded below by external and internal sphincter muscles

The Rectum and anus

Anorectal ring Anoderm and Hilton’s line

Dentate line (pectinate line)

Dentate line (pectinate line)

Transition between the visceral area above and the somatic area below

2cm above & below this line forms “surgical anal canal”

Anal columns Anal crypts

The Dentate line differntiate

Fusion of proctodeum and post allontoic gut

Between cubical epithelium from squamous epithelium

Autonomic Nerves from the spinal nerves

Portal venous system to Systemic venous system

Anal glands

80% are submucosal in extent, 8% extend to the internal sphincter, 8% to the longitudinal muscle, 2% to intersphincteric space, and 1% penetrate the external sphincter.

Muscles of Ano-rectum

Ano-Rectal Muscles

ISHIORECTAL FOSSA --- The ischiorectal fossa is a pyramid shaped space . The apex is formed at the origin of the levator ani from the obturator fascia and the inferior boundary is the skin of the perineum . The anterior boundary is formed by the superficial & deep transversus pernei muscles and the posterior boundary of the perinei membrane. The posterior boundary is made up of the sacrotuberous ligament and the lower boarder of the Gluteus maximus muscles . The medial wall is composed of the levator anii muscles and the external sphincter muscles including the fascia that covers them . The lateral wall is nearly vertical , is formed by the obturator internus muscles, where it lies on the ischium & by the obturator fascia., in the obturator fascia ,on the lateral wall is alcocks canal which contains the internal pudendal vessels and pudendal nerve.

The contents of the ischiorectal fossa include a pad of fat , the inferior rectal nerve coursing from the back of the ischiorectal fossa forward and medially to the external sphincter ,interior

rectal vessels ,portions of scrotal nerves & vessels in men and labial in women, the transverse perineal vessels and the pernial branch of the fourth sacral nerve running to the external sphincter form the posterior angle of the fossa .Anteriorly ischiorectal space has an important extention forward , above the urogenital diaphragm which may become filled with pus in cases of ischirectal abscesses.

Internal anal sphincter

Internal sphincter ( smooth muscle ) Downward and thickened extension of circular

muscle fibres of rectum

Details of Internal sphincter

The length :2.5 cms.

Thickness :2-5 mmColor WhiteFibers Transversely placedAction Spasm or contractureControl Involuntary.

Details of the Internal Sphincter:

Color : Pink

Control : Involuntary

Divisions : Deep, superficial and subcutaneous.

External sphincter

External sphincter

Triple-loop system of Shafik.

The top loop arises and inserts on the pubis and is made up of the deep external sphincter and puborectalis.

The middle loop attaches to the coccyx (superficial external sphincter).

The lower loop inserts in the anterior perianal skin (subcutaneous external sphincter).

Pelvic floor

Arterial supply

Venous drainage

Nerve supply

Internal sphincter sympathetic (L-5) & parasympathetic nerves (S-2, S-3, and S-

4) External sphincter

inferior rectal branch of the pudendal nerve (S-2 ,S-3)

the perineal branch of S-4 Levator ani

sacral roots on its pelvic surface (S-2, S-3, and S-4)

perineal branch of the pudendal nerve

Lymphatic channels of anorectal region

Lymphatic drainage

Upper anal canal Via channels around rectum into pre aortic nodes

Lower anal canal Below dentate lineInguinal nodes

Lymph Nodes In and around

Anal canal

“Everything has been said before , but since not all listen , we have to keep going back

and begin all over again.”

A French author