Difference between revisions of "Rectum - Anatomy & Physiology"

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m (Text replace - "[[Peritoneal cavity - Anatomy & Physiology|" to "[[Peritoneal Cavity - Anatomy & Physiology|")
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*Exists dorsal to the [[Reproductive System - Anatomy & Physiology|reproductive organs]], [[Urinary System - Anatomy & Physiology|bladder]] and [[Urethra - Anatomy & Physiology|urethra]].
 
*Exists dorsal to the [[Reproductive System - Anatomy & Physiology|reproductive organs]], [[Urinary System - Anatomy & Physiology|bladder]] and [[Urethra - Anatomy & Physiology|urethra]].
 
*The cranial portion of the rectum is attached to the dorsal body wall by a short mesorectum which is a continuation of the mesocolon.
 
*The cranial portion of the rectum is attached to the dorsal body wall by a short mesorectum which is a continuation of the mesocolon.
*The mesorectum is reflected to continue with the parietal [[Peritoneal cavity - Anatomy & Physiology|peritoneum]] of the pelvic cavity and to cover the [[Urinary System - Anatomy & Physiology|urogenital organs]] ventrally.
+
*The mesorectum is reflected to continue with the parietal [[Peritoneal Cavity - Anatomy & Physiology|peritoneum]] of the pelvic cavity and to cover the [[Urinary System - Anatomy & Physiology|urogenital organs]] ventrally.
 
**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.

Revision as of 15:28, 7 September 2010

Introduction

Section of puppy showing rectum and anus- copyright RVC 2008

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.

Structure

  • Exists dorsal to the reproductive organs, bladder and urethra.
  • The cranial portion of the rectum is attached to the dorsal body wall by a short mesorectum which is a continuation of the mesocolon.
  • The mesorectum is reflected to continue with the parietal peritoneum of the pelvic cavity and to cover the urogenital organs ventrally.
    • This forms the rectogenital pouch.
    • 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.
      • The retroperitoneal space is filled with soft tissue rich in fat.

Function

Defeacation

  • After the mass movements of the 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) 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.

Histology

Species Differences

Carnivore

  • Control over the external anal sphincter is learned early in life.
  • Defeaction reflex increased by contraction of the abdominal muscles and closure of the vocal cords to increase the pressure in the abdominal cavity.

Ruminant

  • Appears to lack the ability to control the external anal sphincter.

Equine

  • Appears to lack the ability to control the external anal sphincter.

Test yourself with the Rectum flashcards

Links