Changes

The anus is the terminal portion of the alimentary tract which communicates with the external environment. Two sphincters control it's aperture. It allows faeces and gas to leave the body. Defeacation is the process where faeces are expelled from the [[Rectum - Anatomy & Physiology|rectum]] through the anus.

 

The anus is the terminal portion of the '''alimentary tract''' which communicates with the external environment. Two '''sphincters''' control it's aperture. It allows faeces and gas to leave the body. '''Defeacation''' is the process where faeces are expelled from the [[Rectum - Anatomy & Physiology|rectum]] through the anus.

==Structure==

==Structure==

[[Image:Sheep Anus.jpg|thumb|right|150px|Anus (Sheep) - © RVC 2008]]

[[Image:Sheep Anus.jpg|thumb|right|250px|Anus (Sheep) - © RVC 2008]]

*There are ''two'' anal sphincters:

 

**'''Internal anal sphincter''', formed by thickening of the circular smooth muscle of the gut and under autonomic control.

There are ''two'' anal sphincters:

**'''External anal sphincter''', formed from striated skeletal muscle and under voluntary control.

The '''internal anal sphincter''', formed by the thickening of the circular smooth muscle of the gut and under autonomic control and the '''external anal sphincter''', formed from striated skeletal muscle and under voluntary control.

==Function==

==Function==

==Species Differences==

==Species Differences==

===Carnivore===

===Carnivore===

*The dog and cat posses two '''anal sacs'''. In the dog, these are the size of a hazlenut.

The dog and cat posses two '''anal sacs'''. In the dog, these are the size of a hazlenut. They are located ventrolaterally between the internal and external anal sphincters. They are large, coiled apocrine tubules that have many '''tubuloalveolar glands''' in their walls. These '''tubuloalveolar glands''' produce a fatty secretion. The '''fundus''' of the sac secretes a potent smelling fluid that drains through a single duct to an opening near the '''anocutaneous juncntion'''.

**Located ventrolaterally between the internal and external anal sphincters.

The anal sacs get compressed during defecation, which causes the fluid to be expressed. The scent of the fluid is thought to act as a territorial marker.

**They are large, coiled apocrine tubules that have many tubuloalveolar glands in their walls.

Anal sacs are clinically important as they are commonly diseased in dogs - frequently, they become enlarged due to accumulated secretion. The '''dog''' has '''perianal glands''' that lie in the skin surrounding the anus. They are modified sebaceous glands.

***These tubuloalveolar glandsw produce a fatty secretion.

**The fundus of the sac secretes a potent smelling fluid that drains through a single duct to an opening near the anocutaneous juncntion.

**The anal sacs get compressed during defecation, which causes the fluid to be expressed. The scent of the fluid is thought to act as a territorial marker.

***Anal sacs are clinically important as they are commonly diseased in dogs - frequently, they become enlarged due to accumulated secretion.

*The '''dog''' has '''perianal glands''' that lie in the skin surrounding the anus.

**They are modified sebaceous glands.

===[[Equine Alimentary System  - Anatomy & Physiology|Equine]]===

===Equine===

Click here for information on the[[Equine Alimentary System  - Anatomy & Physiology|Equine]] anus.

===Porcine===

===Porcine===

*Also have '''anal sacs'''.

Also have '''anal sacs'''.

==Links==

==Links==

*[[Intestines, Small and Large - Pathology|Pathology Of The Small and Large Intestines]]

'''Click here for information on the[[Intestines, Small and Large - Pathology|pathology Of The Small and Large Intestines]].'''

 

[[Category:Large Intestine - Anatomy & Physiology]]

[[Category:Large Intestine - Anatomy & Physiology]]

[[Category:To Do - A&P]]

[[Category:To Do - AimeeHicks]]