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The anal canal is the terminal part of the large intestine
Large intestine

The large intestine is the last part of the digestive system?the final stage of the alimentary canal?in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass this useless feces from the body....
.

It is situated between the rectum
Rectum

The rectum is the final straight portion of the large intestine in some mammals, and the Gastrointestinal tract in others, terminating in the anus....
 and anus
Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to expel feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as coprolite ; food material after all the nutrients have b...
, below the level of the pelvic diaphragm. It lies in the anal triangle
Anal triangle

The anal triangle is the posterior part of the perineum. It contains the anal canal....
 of perineum
Perineum

In human anatomy, the perineum is generally defined as the surface region in both males and females between the pubic symphysis and the coccyx. The perineum is the region of the body inferior to the pelvic diaphragm and between the legs....
 in between the right and left ischiorectal fossae.

In humans it is approximately 2.5 to 4 cm long, extending from the anorectal junction to the anus
Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to expel feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as coprolite ; food material after all the nutrients have b...
. It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen
Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine. By extension, a lumen can also be the inside space of a cellular component or structure, such as the endoplasmic reticulum....
 closed in the form of an anteroposterior slit.

It is differentiated from the rectum by the transition of the internal surface from endodermal to skinlike ectodermal tissue.

The anal canal is divided into two halves, upper and lower.






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The anal canal is the terminal part of the large intestine
Large intestine

The large intestine is the last part of the digestive system?the final stage of the alimentary canal?in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass this useless feces from the body....
.

It is situated between the rectum
Rectum

The rectum is the final straight portion of the large intestine in some mammals, and the Gastrointestinal tract in others, terminating in the anus....
 and anus
Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to expel feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as coprolite ; food material after all the nutrients have b...
, below the level of the pelvic diaphragm. It lies in the anal triangle
Anal triangle

The anal triangle is the posterior part of the perineum. It contains the anal canal....
 of perineum
Perineum

In human anatomy, the perineum is generally defined as the surface region in both males and females between the pubic symphysis and the coccyx. The perineum is the region of the body inferior to the pelvic diaphragm and between the legs....
 in between the right and left ischiorectal fossae.

In humans it is approximately 2.5 to 4 cm long, extending from the anorectal junction to the anus
Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to expel feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as coprolite ; food material after all the nutrients have b...
. It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen
Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine. By extension, a lumen can also be the inside space of a cellular component or structure, such as the endoplasmic reticulum....
 closed in the form of an anteroposterior slit.

It is differentiated from the rectum by the transition of the internal surface from endodermal to skinlike ectodermal tissue.

The anal canal is divided into two halves, upper and lower. The upper half has longitudinal folds or elevations of tunica mucosa. Its mucosa is lined by simple columnar epithelium. Its lower ends are joined together by folds of mucus membrane called anal valves. The upper half of the anal canal is supplied by the superior rectal artery which is a branch of the inferior mesenteric artery.

The lower half of the anal canal is lined by stratified squamous epithelium that blends with the skin.

A whitish line called Hilton's white line indicates the junction between simple columnar epithelium and stratified squamous epithelium.

Additional images


See also

  • Anal columns
    Anal columns

    The lumen of the anal canal presents, in its upper half, a number of vertical folds, produced by an infolding of the mucous membrane and some of the muscular tissue. They are known as the anal columns ....
  • Anal sinuses
    Anal sinuses

    The rectal columns are separated from one another by furrows, or rectal sinuses, which end below in small valve-like folds, termed anal valves....
  • Anal valves
    Anal valves

    The rectal sinuses, end in small valve-like folds, termed anal valves, which join together the lower ends of the rectal columns....
  • Pectinate line
    Pectinate line

    The pectinate line is a line which divides the upper 2/3rds and lower 1/3rd of the anal canal. Developmentally, this line represents the hindgut-proctodeum junction....
  • anus
    Anus

    The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to expel feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as coprolite ; food material after all the nutrients have b...


External links

- "The rectum and anal canal in the male pelvis."