Difference between revisions of "Rectum - Anatomy & Physiology"

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<big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big>
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<big><center>[[Large Intestine - Anatomy & Physiology|'''BACK TO LARGE INTESTINE - ANATOMY & PHYSIOLOGY''']]</center></big>
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==Introduction==
 
==Introduction==
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[[Image:Puppy rectum-anus.JPG|thumb|right|250px|Section of puppy showing rectum and anus copyright RVC 2008]]
 
  
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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==
  
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The rectum exists dorsal to the [[Reproductive System Overview - Anatomy & Physiology|reproductive organs]], [[Urinary System Overview - 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 mesorectum is reflected to continue with the parietal [[Peritoneal Cavity - Anatomy & Physiology|peritoneum]] of the pelvic cavity and to cover the [[Urinary System Overview - Anatomy & Physiology|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 and 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.
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*Exists dorsal to the [[Reproductive System|reproductive organs]], [[Urinary System - Anatomy & Physiology|bladder]] and urethra.
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*The cranial portion of the rectum is attached to the dorsal body wall by a short mesorectum which is a continuation of the mesocolon.
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*The mesorectum is reflected to continue with the parietal peritoneum of the pelvic cavity and to cover the urogenital organs ventrally.
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**This forms the '''rectogenital pouch'''.
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**Therefore the most distal part of the rectum is retroperitoneal.
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***This distal, retroperitoneal part is directly attached to the vagina in the female and to the urethra in the male.
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***The retroperitoneal space is filled with soft tissue rich in fat.
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*The '''anal canal''' joins the bowel to the exterior.
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**This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).
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**Before joining the anal canal, the rectum becomes dilated to form the ''rectal ampulla''.
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*At the rectoanal junction, the lumen is constricted by longitudinal folds in the mucosa.
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**These are normally pressed together to occlude the lumen.
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*There are ''two'' anal sphincters:
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**'''Internal anal sphincter''', formed by thickening of the circular smooth muscle of the gut and under autonomic control.
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**'''External anal sphincter''', formed from striated skeletal muscle and under voluntary control.
  
 
==Function==
 
==Function==
  
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'''Defeacation'''
 
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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.
 
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==Species Differences==
 
  
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===Carnivore===
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==Vasculature==
  
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Carnivore's control over the external anal sphincter is learned early in life. The defeaction reflex is increased by contraction of the abdominal muscles and closure of the vocal cords to increase the pressure in the abdominal cavity.
 
  
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===Ruminant===
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==Innervation==
  
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Ruminants appear to lack the ability to control the external anal sphincter.
 
  
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===Equine===
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==Lymphatics==
  
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Equine species appear to lack the ability to control the external anal sphincter.
 
  
 
==Histology==
 
==Histology==
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[[Image:Recto-Anal Junction.jpg|thumb|right|250px|Recto-Anal Junction, from the [[Gastrointestinal Tract Histology resource|Gastrointestinal tract part 1 PowerPoint]] ]]
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*Epithelium is columnar.
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The epithelium of the rectum is '''columnar'''. '''Goblet cells''' are present in the mucosa.
 
  
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===Recto-Anal Junction===
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==Species Differences==
  
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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.
 
  
 
==Links==
 
==Links==
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'''Click here for information on [[Intestines, Small and Large - Pathology|Pathology Of The Small and Large Intestines]]'''
 
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{{Template:Learning
 
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|flashcards = [[Rectum - Anatomy & Physiology - Flashcards|Anatomy of the Rectum]]
 
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|powerpoints = [[Gastrointestinal Tract Histology resource|Histology of the Gastrointestinal tract, see part 1]]
 
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}}
 
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==Webinars==
 
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<rss max="10" highlight="none">https://www.thewebinarvet.com/clinical-anatomy/webinars/feed</rss>
 
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[[Category:Large Intestine - Anatomy & Physiology]]
 
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[[Category:A&P Done]]
 

Revision as of 14:20, 12 July 2008

BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY
BACK TO LARGE INTESTINE - ANATOMY & PHYSIOLOGY

Introduction

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.
  • The anal canal joins the bowel to the exterior.
    • This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).
    • Before joining the anal canal, the rectum becomes dilated to form the rectal ampulla.
  • At the rectoanal junction, the lumen is constricted by longitudinal folds in the mucosa.
    • These are normally pressed together to occlude the lumen.
  • There are two anal sphincters:
    • Internal anal sphincter, formed by thickening of the circular smooth muscle of the gut and under autonomic control.
    • External anal sphincter, formed from striated skeletal muscle and under voluntary control.

Function

Vasculature

Innervation

Lymphatics

Histology

  • Epithelium is columnar.

Species Differences

Links

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