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Muscular layer
Histological section of the ureter, showing the thick muscular layers surrounding the lumen.
Details
Identifiers
Latin	tunica muscularis
TA98	A05.4.01.010 A05.5.01.021 A05.6.01.004 A05.7.01.004 A05.7.03.011 A05.7.04.009 A05.8.02.008 A08.1.05.010 A08.2.01.006 A08.3.01.010 A09.1.02.012 A09.1.04.010 A09.2.03.007 A09.3.05.009 A09.4.02.011 A09.3.06.003 A09.4.02.018 A09.4.02.027
Anatomical terminology [edit on Wikidata]

Gastrointestinal wall

This article is one of a series on the
General structure Epithelium Mucosa Submucosa Circular muscle Longitudinal muscle Serosa Adventitia
Specific Meissner's plexus Auerbach's plexus
Organs Esophagus Stomach Intestines
v t e

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

Structure

It usually has two layers of smooth muscle:

inner and "circular"
outer and "longitudinal"

However, there are some exceptions to this pattern.

In the stomach, there are three layers to the muscular layer. Stomach contains an additional oblique muscle layer just interior to circular muscle layer.
In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle.
In the vas deferens of the spermatic cord, there are three layers: inner longitudinal, middle circular, and outer longitudinal.
In the ureter, the smooth muscle orientation is opposite that of the GI tract. There is an inner longitudinal and an outer circular layer.

The inner layer of the muscularis externa forms a sphincter at two locations of the gastrointestinal tract:

in the pylorus of the stomach, it forms the pyloric sphincter.
in the anal canal, it forms the internal anal sphincter.

In the colon, the fibres of the external longitudinal smooth muscle layer are collected into three longitudinal bands, the teniae coli.

The thickest muscularis layer is found in the stomach (triple layered) and thus maximum peristalsis occurs in the stomach. Thinnest muscularis layer in the alimentary canal is found in the rectum, where minimum peristalsis occurs.

Function

The muscularis layer is responsible for the peristaltic movements and segmental contractions in and the alimentary canal. The Auerbach's nerve plexus (myenteric nerve plexus) is found between longitudinal and circular muscle layers, it starts muscle contractions to initiate peristalsis.

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

External links

Muscularis externa of the colon^{[dead link‍]} - BioWeb at University of Wisconsin System
Smooth muscle layers of the gut^{[dead link‍]} - BioWeb at University of Wisconsin System
UIUC Histology Subject 23
Histology image: 11601ooa – Histology Learning System at Boston University — "Muscle Tissue: smooth muscle, muscularis externa"

Anatomy of the gastrointestinal tract, excluding the mouth

Upper

Pharynx	Muscles Spaces peripharyngeal retropharyngeal parapharyngeal retrovisceral danger prevertebral Pterygomandibular raphe Pharyngeal raphe Buccopharyngeal fascia Pharyngobasilar fascia Pyriform sinus
Esophagus	Sphincters upper lower glands crop
Stomach	Curvatures greater lesser Angular incisure Cardia Body Fundus Pylorus Gastric mucosa Gastric folds Microanatomy Gastric pits Gastric glands Cardiac glands Fundic glands Pyloric glands Foveolar cells Parietal cells Gastric chief cells Enterochromaffin-like cells

Lower

Small intestine

Microanatomy	Intestinal villi Microvilli Intestinal glands Enterocytes Enteroendocrine cells Goblet cells Paneth cells
Duodenum	Suspensory muscle Major duodenal papilla Minor duodenal papilla Duodenojejunal flexure Brunner's glands
Jejunum	No substructures
Ileum	Ileocecal valve Peyer's patches Microfold cells

Large intestine

Cecum	Appendix
Colon	Ascending colon Hepatic flexure Transverse colon Splenic flexure Descending colon Sigmoid colon Continuous taenia coli haustra epiploic appendix
Rectum	Transverse folds Ampulla
Anal canal	Anus Anal columns Anal valves Anal sinuses Pectinate line Internal anal sphincter Intersphincteric groove External anal sphincter

Wall

Anatomy of the urinary system

Kidneys

Layers

Fascia
Capsule
Cortex
- column
Medulla
- pyramids
- medullary interstitium
Sinus
Lobe
Cortical lobule
Medullary ray
Nephron

Circulation

Arteries
Veins

Nephron

Renal corpuscle	Glomerulus Bowman's capsule Glomerular basement membrane Podocyte Filtration slits Mesangium Intraglomerular mesangial cell
Renal tubule	Proximal convoluted tubule Loop of Henle Descending Thin ascending Thick ascending Distal convoluted tubule Collecting duct system Connecting tubule Papillary duct Tubular fluid Renal papilla Minor calyx Major calyx Renal pelvis
Juxtaglomerular apparatus	Macula densa Juxtaglomerular cells Mesangium Extraglomerular mesangial cell

Ureters

Ureteropelvic junction

Bladder

Circulation
- Vesical arteries
- Vesical veins
- Vaginal artery (female)
Detrusor muscle
Median umbilical ligament
Trigone

Urethra

Internal urethral orifice
Urethral sphincters
- External
  - male
  - female
- Internal
Male urethra
Urinary meatus

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