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Structure of intestinal musculature

Giorgio Gabella

10.1002/cphy.cp060102

Source: Supplement 16: Handbook of Physiology, The Gastrointestinal System, Motility and Circulation

Originally published: 1989

Published online: January 2011

Full Article on Wiley Online Library



Abstract

The sections in this article are:

1 Arrangement Of Intestinal Muscles
2 Extracellular Materials
3 Smooth Muscle Cells
3.1 Cell Size and Shape
3.2 Caveolae
3.3 Dense Bands
3.4 Sarcoplasmic Reticulum
3.5 Mitochondria and Other Organelles
4 Cell Junctions
4.1 Gap Junctions
4.2 Intermediate Junctions
4.3 Basal Lamina and Cell‐to‐Stroma Junctions
4.4 Terminal Apparatus of Muscle Cells and Cell‐to‐Tendon Junctions
5 Filaments
5.1 Actin Filaments
5.2 Myosin Filaments
5.3 Intermediate Filaments
5.4 Dense Bodies
6 Structural Changes During Contraction
7 Other Cell Types
8 Submucosa
9 Development Of Intestinal Musculature
10 Hypertrophy Of Intestinal Musculature
Figure 1. Figure 1.

Transverse‐longitudinal (transverse to thickness of wall and parallel to length of gut) section of wall of guinea pig ileum is unstained and photographed in phase‐contrast microscopy, cm, Circular muscle (showing also several capillaries); lm, longitudinal muscle; mp, ganglion of myenteric plexus; sad, small and dark muscle cell layer at inner aspect of circular muscle; ser, serosa; sm, submucosa. Calibration bar, 50 μm.
Figure 2. Figure 2.

Electron micrograph of chicken small intestine. Muscle cells of longitudinal muscle (right) are in longitudinal section; those of circular layer are in transverse section. Between muscle layers is part of interstitial cell; nerve bundle runs in circular layer. Presence of conspicuous dense bodies of circular outline and large size is characteristic of avian smooth muscles. Calibration bar, 2 μm.
Figure 3. Figure 3.

Section of taenia of guinea pig cecum photographed unstained in phase‐contrast microscopy. Packing density of muscle cell profiles in this preparation is 90,000/mm2. Septa of connective tissue are arranged mainly radially. Calibration bar, 50 μm.
Figure 4. Figure 4.

Rabbit proximal colon. A: outer aspect. Wide, straight band along middle, the principal taenia, with prominent haustrations on both sides. Calibration bar, 10 μm. B: colon has been split open, flattened out, and transilluminated, mucosal side up. Three arrays of haustrations are separated by regions occupied by taeniae. Calibration bar, 10 μm. C: ring of colon shows positions of taeniae (arrowheads). Pouchlike haustrations are delimited by transverse folds that project deeply into lumen. Calibration bar, 5 mm. D: transverse‐orthogonal section of wall (transverse to thickness of wall and orthogonal to length of gut). Taenia (right) is approximately as thick as underlying circular muscle. Calibration bar, 50 μm. E: higher magnification of taenia in transverse section. Elastic fibers appear as dark dots between muscle cells. Calibration bar, 25 μm. F: tangential section (parallel to serosa) of taenia shows abundance of elastic fibers and their arrangement among muscle cells. Calibration bar, 25 μm.

From Gabella 54
Figure 5. Figure 5.

Electron micrographs of innermost portion of circular muscle layer. A: sheep ileum in transverse‐longitudinal section (transverse to thickness of wall and parallel to length of gut). Bottom, a few ordinary muscle cells cut transversely; top, part of submucosa; middle, layer of small and dark (sad) muscle cells that run close to several elastic fibers (arrows). B: guinea pig ileum in transverse‐orthogonal section (transverse to thickness of wall and orthogonal to length of gut). Bottom, ordinary muscle cell, cut longitudinally, shows mitochondria, filaments, sarcoplasmic reticulum, and caveolae. Top, 2 or 3 small and dark muscle cells (sad) surrounded by elastic fibers (arrows), collagen, and abundant amorphous material of extracellular space. Calibration bars, 1 μm.
Figure 6. Figure 6.

Electron micrograph of muscularis mucosae of guinea pig ileum. Muscle cells in transverse section (left) are nearer to mucosa and run circumferentially. All muscle cells have irregular surface with invaginations (arrow) and processes; they are enmeshed by collagen fibrils (cf). Arrow points to large dense body linked to cell membrane. There are no nerve endings. Calibration bar, 2 μm.
Figure 7. Figure 7.

Electron micrograph of muscle cells of guinea pig taenia coli in longitudinal section. Microtome knife has grazed part of the surface of 2 cells. In these areas cell membrane with attached dense bands (db) and basal lamina are seen en face. Large groups of caveolae (cav), intermingled with sarcoplasmic reticulum, lie between dense bands. Collagen fibrils (cf) run very close to cell surface. Calibration bar, 1 μm.
Figure 8. Figure 8.

Electron migrograph of rabbit taenia coli. Several muscle cells, one displaying nucleus, are surrounded by elastic fibers (ef) and small bundles of collagen fibrils (cf). cav, Caveolae; db, dense bands; mit, mitochondria; sr, sarcoplasmic reticulum of both smooth and granular types. Calibration bar, 1 μm.
Figure 9. Figure 9.

Guinea pig ileum. A and B: intestine is at rest and moderately distended by injection of fluid into lumen. Cells of circular layer have approximately circular profiles (A), whereas cells of longitudinal layer have circumferentially flattened profiles (B). C and D: adjacent segment of intestine was stimulated to contract by 10−5 M carbachol. Both muscle layers thicken. Cells of longitudinal layer have profiles that are large, have a corrugated surface, and are roughly isodiametric (D), the characteristic appearance of contracted muscle cells. Cells of circular layer in same segment of intestine are not contracted, and their profiles are not circular but are flattened radially (C), a passive change in shape due to contraction of longitudinal muscle, cm, Circular muscle; lm, longitudinal muscle. Calibration bar, 100 μm.
Figure 10. Figure 10.

Freeze‐fracture preparation of circular musculature of sheep ileum. Four muscle cells are separated by narrow intercellular spaces in which some collagen fibrils can be seen. Cell a displays P face of its cell membrane; cell b displays E face. Caveolae are grouped into longitudinal rows. There are several gap junctions (some indicated by arrows). Calibration bar, 1 μm.
Figure 11. Figure 11.

Freeze‐fracture preparations of sheep small intestine. A: muscle cell of circular layer shows plasma membrane on its P face pitted with several caveolae. There are 4 gap junctions, ecs, Extracellular space with collagen fibrils. Calibration bar, 0.5 μm. B: gap junction on circular muscle cell seen partly as aggregate of particles on P face of cell membrane and partly as aggregate of pits located on E face of patch of membrane of adjacent muscle cell. Calibration bar, 0.25 μm. C: small gap junction between 2 muscle cells in longitudinal layer of same specimen as in B. Calibration bar, 0.25 μm.
Figure 12. Figure 12.

Freeze‐fracture preparation of muscle cell of human colon. Membrane is exposed on its P face and shows intramembrane particles and 2 rows of caveolae. Many particles are gathered in a ring around neck caveolae. Calibration bar, 0.1 μm.
Figure 13. Figure 13.

Electron micrograph of muscle cell of rabbit taenia coli in longitudinal section. Cell membrane and basal lamina are sectioned very obliquely. Bundles of actin filaments (af) penetrate into dense bands (db), and microfilaments (mf) are associated with basal lamina, cf, Collagen fibrils; ef, elastic fibers; sr, sarcoplasmic reticulum. Calibration bar, 0.5 μm.
Figure 14. Figure 14.

Electron micrograph of muscle cell of guinea pig taenia coli in transverse section, af, Actin filaments; cav, caveolae; cf, collagen fibrils; db, dense bands; if, intermediate filaments; mf, myosin filaments; mit, mitochondria; mt, microtubules; sr, sarcoplasmic reticulum. Profile near center (T) is probably section through a long, tubular invagination of cell membrane. Calibration bar, 0.5 μm.
Figure 15. Figure 15.

Electron micrographs of guinea pig taenia coli show 3 different cell‐to‐cell junctions at same magnification. A: gap junction (macula communicans); B: intermediate junction (macula, or probably fascia, adherens); C: third type of junction, probably of adherens type, with 20‐nm intercellular cleft and less obvious association with intracellular filaments. Calibration bar, 0.2 μm.
Figure 16. Figure 16.

Electron micrographs of guinea pig taenia coli in transverse section. A: tapering end of muscle cell acquires irregular outline that favors cell‐to‐stoma links. Basal lamina is well developed. Extracellular space contains collagen fibrils (cf) and microfibrils (mf) ∼10 nm in diameter. Calibration bar, 0.5 μm. B: elastic fiber running transverse to muscle length passes close to surface of muscle cell. Calibration bar, 0.5 μm. C: terminal apparatus of muscle cell (right of center) with irregular outline and extensive contact with stroma. Adjacent muscle cell (top, left) also displays localized rugosity of its surface matching terminal apparatus and probably linking two cells together. Small nerve bundle is at top right corner. Calibration bar, 1 μm.
Figure 17. Figure 17.

Scanning‐electron micrographs of guinea pig small intestine after digestion of intercellular materials with proteolytic enzymes. A: muscle cell of longitudinal layer ends in many tapering processes. B: muscle cells of circular layer with many processes. One fingerlike process (arrow) penetrates into invagination of adjacent cell. Calibration bars, 1 μm.

From Baluk and Gabella 6
Figure 18. Figure 18.

Electron micrographs of circular musculature of small intestine of turtle (Emys europaea). A: muscle cell in transverse section shows mitochondria (mit), intermediate filaments (if), microtubules (mt), sarcoplasmic reticulum (sr), and clear‐cut bundles of actin filaments (af); dense bodies (db) are large and sharply outlined. Calibration bar, 0.5 μm. B: similar muscle cell profile shows structured appearance of dense bodies. Calibration bar, 0.25 μm C: in muscle cell in longitudinal section large dense body shows its filamentous texture and association with bundles of actin filaments. Calibration bar, 0.5 μm.
Figure 19. Figure 19.

Electron micrographs of guinea pig taenia coli in isotonic contraction (against 1‐g load) in vitro. A: laminar projections of two cells bear caveolae, sarcoplasmic reticulum, and other organelles; myofilaments are approximately parallel to cell length. In extracellular space collagen fibrils run obliquely or almost transversely to cell length. Calibration bar, 0.5 μm. B: center cell shows nucleus with characteristic crenations that develop during isotonic contraction. Calibration bar, 2 μm.
Figure 20. Figure 20.

Section of guinea pig jejunum shows various wall layers. Arrows point to lymphatic vessels in core of villus, across muscularis mucosae, and between circular and longitudinal muscle layers. Calibration bar, 30 μm.
Figure 21. Figure 21.

Electron micrographs of guinea pig taenia coli in transverse section: 4 different configurations of nerve fibers and neuromuscular relations. A: nerve bundle with ∼20 axons, some of which are enlarged and contain vesicles. B: nerve bundle with vesicle‐containing varicosities is completely surrounded by processes of interstitial cell. C: single varicose axon with extensive covering from Schwann cell forms contact with muscle cell. Intercellular clefts measure 30–50 nm. D: single varicose axon with thin process from Schwann cell lies in groove over muscle cell surface. Long intercellular cleft measures <20 nm. Calibration bars, 0.5 μm.
Figure 22. Figure 22.

A transverse section of submucosa of sheep ileum. Several bundles of collagen fibrils cut in different planes are stacked on one another. Calibration bar, 2 μm. B‐D: whole‐mount preparations of submucosa of rat small intestine. Long axis of intestine runs vertically in all 3 micrographs. B: intestine was distended by fluid injected into lumen at 10 cmH2O. C: intestine was distended by placing it around glass rod 5.8 mm in diameter and then compressing gut along its length. This produced change in orientation of collagen fibers. D: intestine was put around glass rod 3.9 mm in diameter and then stretched along its length. Collagen fibers changed their orientation in opposite way from C. Calibration bar (B‐D), 200 μm.
Figure 23. Figure 23.

Schematic representation of wall of small intestine shows orientation of musculature in longitudinal and circular muscle layers and that of collagen fibers in submucosa. A: intestine is moderately distended along both axes (as when fluid is injected into lumen). B: intestine is distended mainly along its length. C: intestine is mainly radially distended.

From Gabella 57
Figure 24. Figure 24.

Electron micrographs of gizzard muscle of chick embryo at day 14. A: several muscle cells in transverse section, abundant mitochondria (mit), dense bodies (db), and sarcoplasmic reticulum (sr). Calibration bar, 1 μm. B: muscle cell undergoing mitotic division. Calibration bar, 2 μm.
Figure 25. Figure 25.

Hypertrophic intestine of guinea pig. A: transverse‐longitudinal section of muscle coat. Size and shape of muscle cells are markedly different from control intestine (see Fig. 1). Ganglion of myenteric plexus lies between muscle layers. B: transverse‐orthogonal section of muscle coat. Muscle cells of circular layer undergo mitosis. Muscle cell profiles of longitudinal layer are much enlarged and irregular in shape, cm, Circular muscle; lm, longitudinal muscle. Calibration bar, 50 μm.


Figure 1.

Transverse‐longitudinal (transverse to thickness of wall and parallel to length of gut) section of wall of guinea pig ileum is unstained and photographed in phase‐contrast microscopy, cm, Circular muscle (showing also several capillaries); lm, longitudinal muscle; mp, ganglion of myenteric plexus; sad, small and dark muscle cell layer at inner aspect of circular muscle; ser, serosa; sm, submucosa. Calibration bar, 50 μm.



Figure 2.

Electron micrograph of chicken small intestine. Muscle cells of longitudinal muscle (right) are in longitudinal section; those of circular layer are in transverse section. Between muscle layers is part of interstitial cell; nerve bundle runs in circular layer. Presence of conspicuous dense bodies of circular outline and large size is characteristic of avian smooth muscles. Calibration bar, 2 μm.



Figure 3.

Section of taenia of guinea pig cecum photographed unstained in phase‐contrast microscopy. Packing density of muscle cell profiles in this preparation is 90,000/mm2. Septa of connective tissue are arranged mainly radially. Calibration bar, 50 μm.



Figure 4.

Rabbit proximal colon. A: outer aspect. Wide, straight band along middle, the principal taenia, with prominent haustrations on both sides. Calibration bar, 10 μm. B: colon has been split open, flattened out, and transilluminated, mucosal side up. Three arrays of haustrations are separated by regions occupied by taeniae. Calibration bar, 10 μm. C: ring of colon shows positions of taeniae (arrowheads). Pouchlike haustrations are delimited by transverse folds that project deeply into lumen. Calibration bar, 5 mm. D: transverse‐orthogonal section of wall (transverse to thickness of wall and orthogonal to length of gut). Taenia (right) is approximately as thick as underlying circular muscle. Calibration bar, 50 μm. E: higher magnification of taenia in transverse section. Elastic fibers appear as dark dots between muscle cells. Calibration bar, 25 μm. F: tangential section (parallel to serosa) of taenia shows abundance of elastic fibers and their arrangement among muscle cells. Calibration bar, 25 μm.

From Gabella 54


Figure 5.

Electron micrographs of innermost portion of circular muscle layer. A: sheep ileum in transverse‐longitudinal section (transverse to thickness of wall and parallel to length of gut). Bottom, a few ordinary muscle cells cut transversely; top, part of submucosa; middle, layer of small and dark (sad) muscle cells that run close to several elastic fibers (arrows). B: guinea pig ileum in transverse‐orthogonal section (transverse to thickness of wall and orthogonal to length of gut). Bottom, ordinary muscle cell, cut longitudinally, shows mitochondria, filaments, sarcoplasmic reticulum, and caveolae. Top, 2 or 3 small and dark muscle cells (sad) surrounded by elastic fibers (arrows), collagen, and abundant amorphous material of extracellular space. Calibration bars, 1 μm.



Figure 6.

Electron micrograph of muscularis mucosae of guinea pig ileum. Muscle cells in transverse section (left) are nearer to mucosa and run circumferentially. All muscle cells have irregular surface with invaginations (arrow) and processes; they are enmeshed by collagen fibrils (cf). Arrow points to large dense body linked to cell membrane. There are no nerve endings. Calibration bar, 2 μm.



Figure 7.

Electron micrograph of muscle cells of guinea pig taenia coli in longitudinal section. Microtome knife has grazed part of the surface of 2 cells. In these areas cell membrane with attached dense bands (db) and basal lamina are seen en face. Large groups of caveolae (cav), intermingled with sarcoplasmic reticulum, lie between dense bands. Collagen fibrils (cf) run very close to cell surface. Calibration bar, 1 μm.



Figure 8.

Electron migrograph of rabbit taenia coli. Several muscle cells, one displaying nucleus, are surrounded by elastic fibers (ef) and small bundles of collagen fibrils (cf). cav, Caveolae; db, dense bands; mit, mitochondria; sr, sarcoplasmic reticulum of both smooth and granular types. Calibration bar, 1 μm.



Figure 9.

Guinea pig ileum. A and B: intestine is at rest and moderately distended by injection of fluid into lumen. Cells of circular layer have approximately circular profiles (A), whereas cells of longitudinal layer have circumferentially flattened profiles (B). C and D: adjacent segment of intestine was stimulated to contract by 10−5 M carbachol. Both muscle layers thicken. Cells of longitudinal layer have profiles that are large, have a corrugated surface, and are roughly isodiametric (D), the characteristic appearance of contracted muscle cells. Cells of circular layer in same segment of intestine are not contracted, and their profiles are not circular but are flattened radially (C), a passive change in shape due to contraction of longitudinal muscle, cm, Circular muscle; lm, longitudinal muscle. Calibration bar, 100 μm.



Figure 10.

Freeze‐fracture preparation of circular musculature of sheep ileum. Four muscle cells are separated by narrow intercellular spaces in which some collagen fibrils can be seen. Cell a displays P face of its cell membrane; cell b displays E face. Caveolae are grouped into longitudinal rows. There are several gap junctions (some indicated by arrows). Calibration bar, 1 μm.



Figure 11.

Freeze‐fracture preparations of sheep small intestine. A: muscle cell of circular layer shows plasma membrane on its P face pitted with several caveolae. There are 4 gap junctions, ecs, Extracellular space with collagen fibrils. Calibration bar, 0.5 μm. B: gap junction on circular muscle cell seen partly as aggregate of particles on P face of cell membrane and partly as aggregate of pits located on E face of patch of membrane of adjacent muscle cell. Calibration bar, 0.25 μm. C: small gap junction between 2 muscle cells in longitudinal layer of same specimen as in B. Calibration bar, 0.25 μm.



Figure 12.

Freeze‐fracture preparation of muscle cell of human colon. Membrane is exposed on its P face and shows intramembrane particles and 2 rows of caveolae. Many particles are gathered in a ring around neck caveolae. Calibration bar, 0.1 μm.



Figure 13.

Electron micrograph of muscle cell of rabbit taenia coli in longitudinal section. Cell membrane and basal lamina are sectioned very obliquely. Bundles of actin filaments (af) penetrate into dense bands (db), and microfilaments (mf) are associated with basal lamina, cf, Collagen fibrils; ef, elastic fibers; sr, sarcoplasmic reticulum. Calibration bar, 0.5 μm.



Figure 14.

Electron micrograph of muscle cell of guinea pig taenia coli in transverse section, af, Actin filaments; cav, caveolae; cf, collagen fibrils; db, dense bands; if, intermediate filaments; mf, myosin filaments; mit, mitochondria; mt, microtubules; sr, sarcoplasmic reticulum. Profile near center (T) is probably section through a long, tubular invagination of cell membrane. Calibration bar, 0.5 μm.



Figure 15.

Electron micrographs of guinea pig taenia coli show 3 different cell‐to‐cell junctions at same magnification. A: gap junction (macula communicans); B: intermediate junction (macula, or probably fascia, adherens); C: third type of junction, probably of adherens type, with 20‐nm intercellular cleft and less obvious association with intracellular filaments. Calibration bar, 0.2 μm.



Figure 16.

Electron micrographs of guinea pig taenia coli in transverse section. A: tapering end of muscle cell acquires irregular outline that favors cell‐to‐stoma links. Basal lamina is well developed. Extracellular space contains collagen fibrils (cf) and microfibrils (mf) ∼10 nm in diameter. Calibration bar, 0.5 μm. B: elastic fiber running transverse to muscle length passes close to surface of muscle cell. Calibration bar, 0.5 μm. C: terminal apparatus of muscle cell (right of center) with irregular outline and extensive contact with stroma. Adjacent muscle cell (top, left) also displays localized rugosity of its surface matching terminal apparatus and probably linking two cells together. Small nerve bundle is at top right corner. Calibration bar, 1 μm.



Figure 17.

Scanning‐electron micrographs of guinea pig small intestine after digestion of intercellular materials with proteolytic enzymes. A: muscle cell of longitudinal layer ends in many tapering processes. B: muscle cells of circular layer with many processes. One fingerlike process (arrow) penetrates into invagination of adjacent cell. Calibration bars, 1 μm.

From Baluk and Gabella 6


Figure 18.

Electron micrographs of circular musculature of small intestine of turtle (Emys europaea). A: muscle cell in transverse section shows mitochondria (mit), intermediate filaments (if), microtubules (mt), sarcoplasmic reticulum (sr), and clear‐cut bundles of actin filaments (af); dense bodies (db) are large and sharply outlined. Calibration bar, 0.5 μm. B: similar muscle cell profile shows structured appearance of dense bodies. Calibration bar, 0.25 μm C: in muscle cell in longitudinal section large dense body shows its filamentous texture and association with bundles of actin filaments. Calibration bar, 0.5 μm.



Figure 19.

Electron micrographs of guinea pig taenia coli in isotonic contraction (against 1‐g load) in vitro. A: laminar projections of two cells bear caveolae, sarcoplasmic reticulum, and other organelles; myofilaments are approximately parallel to cell length. In extracellular space collagen fibrils run obliquely or almost transversely to cell length. Calibration bar, 0.5 μm. B: center cell shows nucleus with characteristic crenations that develop during isotonic contraction. Calibration bar, 2 μm.



Figure 20.

Section of guinea pig jejunum shows various wall layers. Arrows point to lymphatic vessels in core of villus, across muscularis mucosae, and between circular and longitudinal muscle layers. Calibration bar, 30 μm.



Figure 21.

Electron micrographs of guinea pig taenia coli in transverse section: 4 different configurations of nerve fibers and neuromuscular relations. A: nerve bundle with ∼20 axons, some of which are enlarged and contain vesicles. B: nerve bundle with vesicle‐containing varicosities is completely surrounded by processes of interstitial cell. C: single varicose axon with extensive covering from Schwann cell forms contact with muscle cell. Intercellular clefts measure 30–50 nm. D: single varicose axon with thin process from Schwann cell lies in groove over muscle cell surface. Long intercellular cleft measures <20 nm. Calibration bars, 0.5 μm.



Figure 22.

A transverse section of submucosa of sheep ileum. Several bundles of collagen fibrils cut in different planes are stacked on one another. Calibration bar, 2 μm. B‐D: whole‐mount preparations of submucosa of rat small intestine. Long axis of intestine runs vertically in all 3 micrographs. B: intestine was distended by fluid injected into lumen at 10 cmH2O. C: intestine was distended by placing it around glass rod 5.8 mm in diameter and then compressing gut along its length. This produced change in orientation of collagen fibers. D: intestine was put around glass rod 3.9 mm in diameter and then stretched along its length. Collagen fibers changed their orientation in opposite way from C. Calibration bar (B‐D), 200 μm.



Figure 23.

Schematic representation of wall of small intestine shows orientation of musculature in longitudinal and circular muscle layers and that of collagen fibers in submucosa. A: intestine is moderately distended along both axes (as when fluid is injected into lumen). B: intestine is distended mainly along its length. C: intestine is mainly radially distended.

From Gabella 57


Figure 24.

Electron micrographs of gizzard muscle of chick embryo at day 14. A: several muscle cells in transverse section, abundant mitochondria (mit), dense bodies (db), and sarcoplasmic reticulum (sr). Calibration bar, 1 μm. B: muscle cell undergoing mitotic division. Calibration bar, 2 μm.



Figure 25.

Hypertrophic intestine of guinea pig. A: transverse‐longitudinal section of muscle coat. Size and shape of muscle cells are markedly different from control intestine (see Fig. 1). Ganglion of myenteric plexus lies between muscle layers. B: transverse‐orthogonal section of muscle coat. Muscle cells of circular layer undergo mitosis. Muscle cell profiles of longitudinal layer are much enlarged and irregular in shape, cm, Circular muscle; lm, longitudinal muscle. Calibration bar, 50 μm.

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Article Title: Structure of intestinal musculature
 

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Giorgio Gabella. Structure of intestinal musculature. Compr Physiol 2011, Supplement 16: Handbook of Physiology, The Gastrointestinal System, Motility and Circulation: 103-139. First published in print 1989. doi: 10.1002/cphy.cp060102