Changes

==Introduction==

==Introduction==

The rectum lies between the terminal portion of the descending colon and anus. It is empty most of the time, except after the mass movements of the 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.

==Structure==

==Structure==

**This forms the '''rectogenital pouch'''.

**This forms the '''rectogenital pouch'''.

**Therefore the most distal part of the rectum is retroperitoneal.

**Therefore the most distal part of the rectum is retroperitoneal.

***This distal, retroperitoneal part is directly attached to the vagina in the female and to the urethra in the male.

***This distal, retroperitoneal part is directly attached to the [[Female Reproductive Tract -The Vagina/Vestibule - Anatomy & Physiology|vagina]] in the female and to the [[Urethra - Anatomy & Physiology|urethra]] in the male.

***The retroperitoneal space is filled with soft tissue rich in fat.

***The retroperitoneal space is filled with soft tissue rich in fat.

'''Defeacation'''

'''Defeacation'''

*After the mass movements of the large intestine, the rectum becomes filled with faeces.

*After the mass movements of the [[Large Intestine - Anatomy & Phsyiology|large intestine]], the rectum becomes filled with faeces.

*This stimulates pressue sensitive cells in the wall of the rectum and initiates the defeacation reflex.

*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.

*The reflex causes a forceful contraction of the rectum, and relaxation of the internal anal sphincter.