Anal canal

anal vergeanal tract
The anal canal is the terminal part of the large intestine.wikipedia
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Large intestine

coloncolorectallarge bowel
The anal canal is the terminal part of the large intestine.
Most sources define the large intestine as the combination of the cecum, colon, rectum, and anal canal.

Rectum

rectalrectallyrectal ampulla
It is situated between the rectum and anus, below the level of the pelvic diaphragm.
In humans, the rectum is followed by the anal canal which is about 4 cm long, before the gastrointestinal tract terminates at the anal verge.

Anal triangle

It lies in the anal triangle of perineum in between the right and left ischioanal fossa.
It contains the anal canal.

Pectinate line

dentate line
The lower half of the anal canal, below the pectinate line, is divided into two zones separated by Hilton's white line.
The pectinate line (dentate line) is a line which divides the upper two thirds and lower third of the anal canal.

Intersphincteric groove

Hilton's white lineHilton's Line
The lower half of the anal canal, below the pectinate line, is divided into two zones separated by Hilton's white line.
Intersphincteric groove or Hilton's white line is a boundary in the anal canal.

Pelvic floor

pelvic diaphragmpelvic floor musclespelvic muscles
It is situated between the rectum and anus, below the level of the pelvic diaphragm.
The pelvic floor has two hiatuses (gaps): Anteriorly urogenital hiatus through which urethra and vagina pass through and posteriorly rectal hiatus through which anal canal passes.

Stratified squamous epithelium

stratified squamousstratified epitheliumstratified squamous epithelia
The two parts are the zona hemorrhagica and zona cutanea, lined by stratified squamous non-keratinized and stratified squamous keratinized epithelium, respectively.
Examples of non-keratinized stratified squamous epithelium include corneal epithelium, lining mucosa of oral cavity, esophagus, anal canal, ectocervix, vagina, foreskin, and the internal portion of the lips.

Anal gland

anal sacanal glandsanal scent glands
Behind this lies the anal gland which secretes lymphal discharge and built up fecal matter from the colon lining.
The anal glands are in the wall of the anal canal.

Inferior rectal artery

inferiorinferior hemorrhoidal arteriesinferior rectal arteries
The inferior rectal artery (inferior hemorrhoidal artery) is an artery that supplies blood to the lower half of the anal canal.

Anus

analperianalanal opening
It is situated between the rectum and anus, below the level of the pelvic diaphragm.

Anal sinuses

anal sinussinuses
The anal sinuses (rectal sinuses) are furrows in the anal canal, that separate the anal columns from one another.

Internal anal sphincter

internalSphincter ani internusanal sphincter
The internal anal sphincter, IAS, (or sphincter ani internus) is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal; its inferior border is in contact with, but quite separate from, the external anal sphincter.

Mucous membrane

mucosamucous membranesmucosal
Exceptions include the palate, cheeks, floor of the mouth, gums, lips and the portion of the anal canal below the pectinate line, which are all ectodermal in origin.

Perineum

perinealperineal bodyanogenital
It lies in the anal triangle of perineum in between the right and left ischioanal fossa.

Anal columns

Columns of Morgagni
Anal columns (Columns of Morgagni or less commonly Morgagni's columns) are a number of vertical folds, produced by an infolding of the mucous membrane and some of the muscular tissue in the upper half of the lumen of the anal canal.

Internal pudendal artery

Dorsal artery of clitorisdeep artery of clitorisinternal pudendal vessels

Levator ani

pubococcygeus musclepubococcygeuspuborectalis
The pubococcygeus arises from the back of the pubis and from the anterior part of the obturator fascia, and is directed backward almost horizontally along the side of the anal canal toward the coccyx and sacrum, to which it finds attachment.

External anal sphincter

anal sphincterSphincter ani externus muscleSphincter ani externus
(1) It is, like other muscles, always in a state of tonic contraction, and having no antagonistic muscle it keeps the anal canal and orifice shut.

Proctodeum

proctodeal
It will form the lower part of the anal canal, below the pectinate line, which will be lined by stratified squamous non-keratinized (zona hemorrhagica) and stratified squamous keratinized (zona cutanea) epithelium.

Inferior anal nerves

inferior rectal nerveinferior rectal nervesInferior rectal
The Inferior rectal nerves (inferior anal nerves, inferior hemorrhoidal nerve) usually branch from the pudendal nerve but occasionally arises directly from the sacral plexus; they cross the ischiorectal fossa along with the inferior rectal artery and veins, toward the anal canal and the lower end of the rectum, and is distributed to the Sphincter ani externus (external anal sphincter, EAS) and to the integument (skin) around the anus.

Ischioanal fossa

ischiorectal fossaIschio-anal fossa
It lies in the anal triangle of perineum in between the right and left ischioanal fossa.

Simple columnar epithelium

simple columnarciliated columnar epitheliumciliated simple columnar epithelium
The zona columnaris is the upper half of the canal and is lined by simple columnar epithelium.

Lumen (anatomy)

lumenluminalintraluminal
It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen closed in the form of an anteroposterior slit.

Endoderm

endodermalEntodermdefinitive endoderm
It is differentiated from the rectum by the transition of the internal surface from endodermal to skin-like ectodermal tissue.