ANATOMY OF ANAL

CANALPresented by : AYESHA JALIL

Roll# 43

What is ANAL CANAL?

SURGICAL ANATOMY The anal canal is about

1.5”(4 cm) long,

commences at the level

where the rectum passes

through the pelvic

diaphragm, downward and

backward from rectal

ampulla and ends at the

anal verge

LOCATION PELVIS

PERINEUM

ANAL TRIANGLE

RELATIONS

POSTERIORLY

Anococcygeal body

LATERALLY

Ischiorectal fossas

ANTERIORLY IN MALE

Perineal body

Urogenital diaphragm

Membranous part of urethra

Bulb of penis

ANTERIORLY IN FEMALE

Perineal body

Urogenital diaphragm

Lower part of vagina

STRUCTURE EMBRYOLOGY

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

UPPER HALF(2/3) LOWER HALF(1/3)

STRUCTURE

Mucous membrane of upper

half of anal canal is derived

from hindgut entoderm.

It is lined by columnar

epithelium

It is thrown into vertical folds

called anal columns, which

are joined together at their

lower end by semilunar folds

called anal valves(remains of

proctodeal membrane).

Nerve supply is derived from

autonomic hypogastric plexus.

It is sensitive to stretch only.

Mucous membrane of lower half is derived from ectoderm of anal pit.

It is lined by stratified squamous epithelium.

There are no anal columns

• The nerve supply is from somatic inferior rectal nerve.; it is thus sensitive to pain, temperature, touch and pressure.

BLOOD SUPPLY

VENOUS DRAINAGE

LYMPHATIC DRAINAGE

The arterial supply is that of hindgut- superior rectal artery, branch of inferior mesenteric artery.

The venous drainage is by the superior rectal vein, a tributary of inferior mesenteric vein, and the portal vein.

The lymphatic drainage is to the pararectal nodes and then eventually to inferior mesenteric nodes.

The arterial supply is inferior rectal artery, a branch of internal pudendal artery.

The venous drainage is by inferior rectal vein, a tributary of the internal pudendal vein, which drains into the internal iliac vein.

The lymphatic drainage is downward to the medial group of superficial inguinal nodes.

NERVE SUPPLY

IMPORTANT!!! When considering metastasis of cancer cells, tumors in

superior part are painless, and those in inferior part painful.

MUSCULARIS EXTERNA As in the upper parts of GIT, it is divided into an outer

longitudinal and inner circular layer of smooth muscle.

ANAL FOLDS AND COLUMNS The mucosa and submucosa above the dentate line is

uneven and thrown into folds, the so-called anal cushions.

there are usually three, the left lateral, right posterior and

right anterior positions, and they continue proximally as the

primary rectal foldings. Secondary foldings (the rectal

columns of Morgagni) lie both over and between the primary

folds.

MUCOSA SUSPENSORY

LIGAMENT the increased density of fibres that insert into the mucosa of

the anal crypts at the level of the dentate line, termed the

‘mucosal suspensory Ligament.

INVOLUNTARY INTERNAL VOLUNTARY EXTERNAL

ANAL SPHINCTERS

2-5 mm of thickening of the smooth muscle of the circular coat at the upper end of the anal canal.

Supplied by autonomic plexus and remains in tonic state of contraction.

It has three parts

Subcutaneous

Superficial

Deep

Supplied by pudendal

nerve.

ANORECTAL RING At the junction of rectum

and anal canal, the internal

sphincter, the deep part of

external sphincter,

conjoined longitudinal

muscle and puborectalis

muscles form anorectal

ring.

INTERSPHINCTERIC PLANE Between the external

sphincter muscle laterally and the longitudinal muscle medially exists a potential space, the intersphinctericplane.

IMPORTANCE

Contains anal glands

Route for spread of pus

The plane can be opened up surgically to provide access for operations on the sphincter muscles.

HILTON’S LINEALSO CALLED WHITE LINE/ANOCUTANEOUS INE.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.

Ischiorectal abscess when communicates with anal canal

usually opens at or below Hilton’s line.

ANAL GLANDS Anal glands may be found in the submucosa and

intersphincteric space, and normally number between 0 and

10 in an individual.

Their function is unknown, although they secrete mucin.

which perhaps lubricates the anal canal to ease defaecation.

The importance of intersphincteric anal glands is that they

are widely considered to be the potential source of anal

sepsis, either acute, presenting as perianal, ischiorectal or

even pelvic sepsis, or chronic, presenting as a

cryptoglandular (non-specific) anal fistula.