Muscularis externa

Muscularis externa
LAYERS: serosa longitudinal muscle myenteric plexus circular muscle submucosal plexus submucosal mucosal
Transverse section of ureter.
Latin	tunica muscularis

The muscular coat (muscular layer, muscular fibers, muscularis propria, muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa membrane. It is responsible for gut movement such as peristalsis.

It usually has two distinct layers of smooth muscle:

• inner and "circular"
• outer and "longitudinal"

However, there are some exceptions to this pattern.

• In the stomach and colon, there are three layers to the muscularis externa.
• In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle.

The inner layer of the muscularis externa forms a sphincter at two locations of the alimentary canal:

• in the pyloric stomach, it forms the pyloric sphincter
• in the anal canal, it forms the anal sphincter

Additional images

Wall of the ureter.	Layers of stomach wall.	Section of the human esophagus. Moderately magnified.	Section of duodenum of cat. X 60.
Vertical section of bladder wall.

External links

• muscular+layer at eMedicine Dictionary
• Histology at nhmccd.edu
• Bioweb at UWLAX Muscularis externa of the colon
• Bioweb at UWLAX Smooth muscle layers of the gut
• Histology at OU 52_05 - "Duodenum"
• Organology at UC Davis Digestive/mammal/system1/system7 - "Mammal, whole system (LM, Low)"
• UIUC Histology Subject 23
• Histology at BU 11601ooa - "Muscle Tissue: smooth muscle, muscularis externa"
• Histology at BU 10802loa - "Digestive System: Alimentary Canal - esophagus "

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated.

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