Changes

==Introduction==

==Introduction==

[[Image:Puppy rectum-anus.JPG|thumb|right|250px|Section of puppy showing rectum and anus- copyright RVC 2008]]

[[Image:Puppy rectum-anus.JPG|thumb|right|250px|Section of puppy showing rectum and anus copyright RVC 2008]]

The rectum lies between the terminal portion of the descending [[Colon - Anatomy & Physiology|colon]] and [[Anus - Anatomy & Physiology|anus]]. It is empty most of the time, except after the mass movements of the [[Large Intestine - Anatomy & Physiology|large intestine]] which move faeces into the rectum. This stimulates defeaction, which may happen when an animal is frightened.

The rectum lies between the terminal portion of the descending [[Colon - Anatomy & Physiology|colon]] and [[Anus - Anatomy & Physiology|anus]]. It is empty most of the time, except after the mass movements of the [[Large Intestine - Anatomy & Physiology|large intestine]] which move faeces into the rectum. This stimulates defeaction, which may happen when an animal is frightened.

'''Defeacation'''

'''Defeacation'''

After the mass movements of the [[Large Intestine - Anatomy & Physiology|large intestine]], the rectum becomes filled with faeces. This stimulates pressue sensitive cells in the wall of the rectum and initiates the defeacation reflex. The reflex causes a forceful contraction of the rectum, and relaxation of the internal anal sphincter. This produces the conscious sensation of the need to empty the bowel. Some species (see [[#Species Differences|species differences]]) are able to voluntarily keep the external anal sphincter closed if defeacation is not suitable in the situation. This reduces the defeaction reflex and reduces the conscious perception of needing to empty the bowel, until another mass movement occurs and a fresh reflex is created.

After the mass movements of the [[Large Intestine - Anatomy & Physiology|large intestine]], the rectum becomes filled with faeces. This stimulates pressure sensitive cells in the wall of the rectum and initiates the defeacation reflex. The reflex causes a forceful contraction of the rectum, and relaxation of the internal anal sphincter. This produces the conscious sensation of the need to empty the bowel. Some species (see [[#Species Differences|species differences]]) are able to voluntarily keep the external anal sphincter closed if defeacation is not suitable in the situation. This reduces the defeaction reflex and reduces the conscious perception of needing to empty the bowel, until another mass movement occurs and a fresh reflex is created.

==Species Differences==

==Species Differences==

Ruminants appear to lack the ability to control the external anal sphincter.

Ruminants appear to lack the ability to control the external anal sphincter.

===[[Hindgut Fermenters - Anatomy & Physiology|Equine]]===

===Equine===

Equine species appear to lack the ability to control the external anal sphincter.

Equine species appear to lack the ability to control the external anal sphincter.

==Histology==

==Histology==

The junction marks the termination of the '''lamina muscularis''' and longitudinal layer of the '''tunica muscularis'''. The circular layer of the '''tunica muscularis''' forms the '''internal anal sphincter'''. The '''external anal sphincter''' is formed from skeletal muscle. At the junction, the epithelium changes from columnar to stratified squamous non-keratinised.

*Termination of the lamina muscularis and longitudinal layer of the tunica muscularis.

*The circular layer of the tunica muscularis forms the internal anal sphincter.

*The external anal sphincter is formed from skeletal muscle.

*Epithelium changes from columnar to stratified squamous non-keratinised.

==Links==

==Links==

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

'''Click here for information on [[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 - AimeeHicks]]

[[Category:A&P Done]]