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| Anal canal | |
|---|---|
 Anatomy of the anus and rectum | |
 Coronal section through the anal canal. B. Cavity ofurinary bladder V.D.Ductus deferens. S.V.Seminal vesicle. R. Second part ofrectum. A.C. Anal canal. L.A.Levator ani. I.S.Sphincter ani internus. E.S.Sphincter ani externus. | |
| Details | |
| Precursor | Hindgut,proctodeum |
| Artery | Superior rectal artery (abovepectinate line) andinferior rectal artery (below line) |
| Vein | Superior rectal vein (above pectinate line) andInferior rectal vein (below line) |
| Nerve | Autonomicinferior hypogastric plexus (above pectinate line) andsomaticinferior rectal nerves (below line) |
| Lymph | Superficial inguinal lymph node (below pectinate line) andinternal iliac lymph nodes (above line) |
| Identifiers | |
| Latin | canalis analis |
| MeSH | D001003 |
| TA98 | A05.7.05.001 |
| TA2 | 3009 |
| FMA | 15703 |
| Anatomical terminology | |
Theanal canal is the part that connects therectum to theanus, located below the level of thepelvic diaphragm.[1] It is located within theanal triangle of theperineum, between the right and leftischioanal fossa. As the final functional segment of thebowel, it functions to regulate release ofexcrement by two muscularsphincter complexes. The anus is the aperture at the terminal portion of the anal canal.
In humans, the anal canal is approximately 2.5 to 4 cm (0.98 to 1.57 in) long, from the anorectal junction to theanus.[2][3][4] It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep thelumen closed in the form of an anteroposterior slit.
The canal is differentiated from the rectum by a transition along the internal surface fromendodermal to skin-likeectodermal tissue.
The anal canal is traditionally divided into two segments, upper and lower, separated by thepectinate line (also known as the dentate line):
Theanal verge refers to thedistal end of the anal canal, a transitional zone between theepithelium of the anal canal and theperianal skin. It should not be confused with the pectinate line between the upper and lower zones within the anal canal.
Theanal gland secretes lymphal discharge and built-upfecal matter from thecolon lining. In some animals this gland expungement can be done routinely every 24–36 months to prevent infection andfistula formation.
Theexternal anal sphincter muscle is the voluntary muscle that surrounds and adheres to the anus at the lower margin of the anal canal. This muscle is in a state oftonic contraction, but duringdefecation, it relaxes to allow the release offeces.
Movement of the feces is also controlled by the involuntarily controlled internal anal sphincter, which is an extension of the circular muscle surrounding the anal canal. It relaxes to expel feces from the rectum and anal canal.
