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Histoanatomy and ultrastructure of vasculature of alimentary tract

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Abstract

The sections in this article are:

1 Vascular Organization of Alimentary Tract
1.1 Vascular Supply and Drainage of Alimentary Tract
1.2 Intramural Distributive Vessels
1.3 Muscle Microvessels
1.4 Vasculature of Enteric Neural Plexuses
1.5 Submucosal Microvessels
1.6 Mucosal Microvessels
2 Microvascular Ultrastructure and Permeability Characteristics
2.1 Small Intestine
2.2 Stomach
2.3 Colon
3 Future Directions for Structural Research in Gastrointestinal Microvasculature
Figure 1. Figure 1.

Scanning electron micrographs of microvascular corrosion casts of gastric tissue of rat and human. A: submucosal aspect of cast of rat gastric corpus mucosa plus submucosa; note parallel branching pattern of submucosal arterioles (A) and venules (V). Fine meshwork between is commencement of mucosal capillary network. Note also occasional fine vessels running in plane of submucosa (arrows). Calibration bar, 1,000 μm. B: fractured edge of mucosal cast of rat gastric corpus showing capillaries are oriented principally perpendicular (arrows) to plane of gastric luminal surface (L); note, however, frequent cross‐connections, which may be important in healing ulcerated gastric mucosa. Calibration bar, 100 μm. C: luminal aspect of cast of mucosal microvasculature of human gastric body. Note polygonal array of most luminal capillaries, which define openings of gastric pits. Some larger mucosal venule tributaries (arrows) are apparent just below most superficial capillaries. Calibration bar, 100 μm. D: fractured edge of partial vascular cast of rat gastric corpus in which only venules and venous ends of capillaries were filled (by retrograde injection of plastic). Mucosal venule (MV) proceeds from its drainage of subsurface capillaries (D) to submucous venous plexus (SMV) without additional capillary tributaries. Note also infrequency of mucosal venules. Calibration bar, 250 μm.

A, B, D from Gannon et al. ; C from Gannon et al.
Figure 2. Figure 2.

Electron micrographs of capillaries of rat stomach. A: capillary (L, lumen) from muscularis externa of rat gastric corpus. Endothelium is continuous, with frequent endothelial vesicles, and is largely surrounded by pericyte processes. M, smooth muscle cells. Calibration bar, 5 μm. B: capillary (L, lumen) of subepithelial plexus that underlies basal epithelial cells (E) of forestomach stratified squamous epithelium. Capillary endothelium is continuous with endothelial vesicles and is largely surrounded by pericyte processes. Calibration bar, 5 μm. C: corrosion vascular cast of rat forestomach: view of gastric luminal aspect of cast. Planar array of fine vessels of subepithelial microvascular plexus overlies larger vessels of submucous vascular plexus. A, arteriole; V, venule. Calibration bar, 250 μm. D: corrosion vascular cast of rat forestomach: view of cut edge of cast. Planar array of subepithelial capillaries (SEC) overlies larger submucosal vascular plexus (SM), with capillary network of muscularis externa layer (MEL) below. Calibration bar, 250 μm.

From Browning et al.
Figure 3. Figure 3.

Microvascular organization of oxyntic mucosa (of stomach) and proposed mechanism for microvascular transport of produced by parietal cells toward surface mucous cells in a local portal pattern (inset).

From Gannon et al.
Figure 4. Figure 4.

Electron micrographs of rat gastric microvessels. A: capillary (L, lumen) adjacent to two parietal cells (PC). Note fenestrations in capillary endothelium and close proximity of capillary to parietal cells (open arrowheads). Calibration bar, 2.5 μm. B: higher magnification of capillary close to parietal cells. Note fenestrae with diaphragm and endothelial vesicles in endothelium, separate basal lamina (BL) of capillary and parietal cell, and mitochondria (M) and canaliculi (CN) of parietal cell. Calibration bar, 1.0 μra. C: corrosion microvascular cast of rat gastric corpus after ethanol‐induced ulcer formation; view of luminal aspect. Note loss of patency of capillaries throughout much of mucosal thickness almost to submucosa in center of field, so that submucous vascular plexus is just seen (arrow); complete mucosa at bottom. In eroded area, mucosal venules (arrowheads) are cast, presumably by retrograde filling; several ruptures of microvessels are evident at top, permitting extrusion of plastic. Calibration bar, 500 μm.

A, B from Gannon et al. ; C from O'Brien et al.
Figure 5. Figure 5.

Mucosal microcirculatory patterns typical of human and rabbit small intestine (except duodenum). VA, villus arteriole; VV, villus venule; solid arrows indicate directions of blood flow; open arrows indicate intraluminal flux of succus entericus from crypts to villi.

Adapted from Casley‐Smith and Gannon
Figure 6. Figure 6.

Scanning electron micrographs of villi of small intestine from several species. A: human villi; note variety of villus shapes. Calibration bar, 500 μm. B: dog villi; note stout cylindrical shape. Calibration bar, 250 μm. C: cat villi; note slender fingerlike shape. Calibration bar, 100 μm. D: rat villi; note leaflike flattened shape. Calibration bar, 250 μm.

A from Gannon et al. ; B, C from Gannon et al.
Figure 7. Figure 7.

Models of villus microcirculatory pattern. A: fountain pattern of villus blood flow; B: tuft pattern; C: stepladder pattern; D: combined fountain supply to villus tip and tuft supply to villus shaft, as described by Casley‐Smith and Gannon for rabbit, rat, and human villi. Dotted lines represent watershed region between two blood flow sources to villi (i.e., direct arterial supply to the villus tip and indirect local portal supply via the periglandular capillaries). This watershed level varies in height up the villus with the species.

Adapted from Gannon
Figure 8. Figure 8.

A: montage of in vivo photomicrographs of rabbit intestinal villus (ex video monitor screen), a, Arteriole; v, venule; arrows, principal directions of capillary blood flow; dotted lines, division between villus tip and shaft blood flows, as shown in Fig. and Fig. D. Calibration bar, 250 μm. B: vascular corrosion cast of rat pylorus and proximal duodenum, bisected along duodenal long axis. PY, pylorus; DV, most proximal duodenal villi; L, duodenal lumen; S, duodenal serosa; area outlined with dotted line, compact mass of Brunner's glands. Calibration bar, 1,000 μm.

A from Gannon ; B from Browning and Gannon
Figure 9. Figure 9.

Scanning and transmission electron micrographs of rat small intestinal villi illustrating myofibroblast‐like cells. A: low power of rat villus, with epithelial sheet removed in foreground; note cellular network of myofibroblast or fibroblast‐like cells (*) that overlie the subepithelial capillary plexus (solid arrows). Open arrows indicate goblet cell apices. Calibration bar, 20 μm. B: higher magnification of fibroblast‐like cell (FLC) network that overlies villus capillaries (arrows). Calibration bar, 5 μm. C: Process of fibroblast‐like cell; note prominent bundle of 6‐nm filaments (arrows) and also rough endoplasmic reticulum with distended cisternae (open arrows), which is characteristic of these cells. Calibration bar, 1.0 μm.

A from Desaki et al. a); B courtesy of J. Desaki and Y. Euhara; C courtesy of J. Desaki
Figure 10. Figure 10.

Micrographs of dog intestinal villi. A: cast of dog intestinal villi. Note completely filled villus tip vessels arrayed in fountain pattern. Calibration bar, 500 μm. B: cast of partially filled dog villi with tips not cast. Capillaries of villus lower shaft connect with capillaries of pericryptal plexus, presumably in tuft pattern. Calibration bar, 250 μm. C: transverse section of cast of dog villi at middle third of villus; incomplete cast with tip region not filled. Villus arteriole (A) serially supplies (white arrow) and villus venule (V) serially drains (black arrow) subepithelial capillary network in stepladder pattern. Calibration bar, 100 μm. D: transverse section at midshaft of dog villus, 1 μm plastic section, polychrome stain. A, arteriole; V, venule; CL, central lacteal; black arrows indicate subepithelial capillaries; E, villus epithelium. Calibration bar, 100 μm.

From Casley‐Smith and Gannon
Figure 11. Figure 11.

Scanning electron micrographs of microvascular corrosion casts of small intestinal villi of four mammalian species. A: human villi. Note difference in size between adjacent villi and connection of villus capillaries to capillary rings surrounding intestinal gland openings. A, arteriole; V, venule. Calibration bar, 100 μm. B: rat villi, duodenum. Note broad flattened villi arrayed across long axis of gut. C, capillary plexus of villus; PC, pericryptal plexus surrounding intestinal glands; A, arteriole; V, venule. Calibration bar, 250 μm. C: cat villi. Note slender form; plexus consists solely of capillaries (C) and an arteriole (A) in tuft pattern, as seen in partially filled villus at bottom left; there is no villus venule. Mucosal venules commence at level of villus base between adjacent villi. Calibration bar, 100 μm. D: rabbit villi. Note arteriolar breakup near tip and villus capillaries connected to plexus surrounding intestinal gland openings (arrows). A, arteriole; V, venule. Calibration bar, 250 μm.

A from Gannon ; B from Browning and Gannon ; C, D from Gannon et al.
Figure 12. Figure 12.

A: major vascular supply and drainage routes of Brunner's gland tissue in rat proximal duodenum. Inset, dorsal view of horizontal schematic section of rat stomach, indicating location of Brunner's glands. B: parallel nature of separate circulations of Brunner's glands and of villus tip and shaft in duodenum. Note that presumably acidified blood (after secretion in Brummer's glands) is not supplied to villi, which have to cope with an exogenous H+ load from duodenal lumen (ex gastric juice).

From Browning and Gannon
Figure 13. Figure 13.

Microvasculature of rat colonic mucosa. A: corrosion microvascular cast of rat midcolon. Constricted muscle and local absence of fecal pellet produces constricted lumen (L). Larger vessels of submucous vascular plexus (SM) are evident, but vasculature of muscularis externa is not filled. Calibration bar, 1,000 μm. B: fractured cast of rat colonic mucosa; oblique view of luminal aspect. Capillaries nearest lumen are arranged in honeycomb‐like plexus surrounding openings of colonic glands (*). Site where mucosal venule commences drainage (D) is also identified. Arterioles (A) branch to capillaries only near submucosal aspect. Calibration bar, 250 μm. C: microcirculatory pattern of rat colonic mucosa; pattern is analogous to that observed in rat and human stomach (cf. Fig. ). D: fenestrated capillary of rat/human colonic mucosa. Colonocytes (C) abut epithelial basal lamina (arrow). Calibration bar, 5 μm.

A, B, C from Browning and Gannon
Figure 14. Figure 14.

Blood and lymph microcirculation of intestinal villus, illustrating closeness of fenestrated capillaries to base of mucosal epithelium.

From Granger
Figure 15. Figure 15.

Cross section of blood capillary in intestinal mucosa of mouse. Endothelial layer (en) consists of single cell whose attenuated part faces intestinal epithelium (ep). Thicker part (perikaryon) contains cellular organelles and faces center of villus. Attenuated part contains numerous fenestrae with diaphragms; their aggregate area amounts to ∼5% of endothelial surface. Thicker part of endothelium is provided with flask‐shaped (v1) and apertured (v2) vesicles. bm, Continuous basement membrane; pc, pericyte pseudopodia. X29,000.

From Clementi and Palade
Figure 16. Figure 16.

Continuous and fenestrated capillary walls. 1–4, Plasmalemmal vesicles, interendo‐thelial junctions, vesicle channels, and fenestrations, respectively. Dimensions of different strictures are indicated in angströms. Schematic transendothelial channel is shown at top, illustrating outer dimensions of channel (500 Å), dimensions of strictures within channel (100–400 Å), and selectivity of diaphragms within channel (50–100 Å).

From Taylor and Granger
Figure 17. Figure 17.

Four consecutive sections through inter‐endothelial junction in rat heart capillary. Arrows mark points of contact between junctional membranes. In serial section, each point of contact appears to open to form a patent pathway through junction around points of membrane apposition. L, lumen.

From Bungaard
Figure 18. Figure 18.

Mean dimensions of inter‐endothelial junctions in lung (top) and skeletal muscle (bottom) capillaries in rabbit. To facilitate comparison, widths of junction are shown going from narrowest values (0–5 nm) on luminal side to widest values (>25 nm) on interstitial side, although in reality various widths occur at random along junction. Only a small proportion (5%) of junction is narrowed to width of 0–5 nm, and remainder of junction opens to a width >5 nm.

From Perry


Figure 1.

Scanning electron micrographs of microvascular corrosion casts of gastric tissue of rat and human. A: submucosal aspect of cast of rat gastric corpus mucosa plus submucosa; note parallel branching pattern of submucosal arterioles (A) and venules (V). Fine meshwork between is commencement of mucosal capillary network. Note also occasional fine vessels running in plane of submucosa (arrows). Calibration bar, 1,000 μm. B: fractured edge of mucosal cast of rat gastric corpus showing capillaries are oriented principally perpendicular (arrows) to plane of gastric luminal surface (L); note, however, frequent cross‐connections, which may be important in healing ulcerated gastric mucosa. Calibration bar, 100 μm. C: luminal aspect of cast of mucosal microvasculature of human gastric body. Note polygonal array of most luminal capillaries, which define openings of gastric pits. Some larger mucosal venule tributaries (arrows) are apparent just below most superficial capillaries. Calibration bar, 100 μm. D: fractured edge of partial vascular cast of rat gastric corpus in which only venules and venous ends of capillaries were filled (by retrograde injection of plastic). Mucosal venule (MV) proceeds from its drainage of subsurface capillaries (D) to submucous venous plexus (SMV) without additional capillary tributaries. Note also infrequency of mucosal venules. Calibration bar, 250 μm.

A, B, D from Gannon et al. ; C from Gannon et al.


Figure 2.

Electron micrographs of capillaries of rat stomach. A: capillary (L, lumen) from muscularis externa of rat gastric corpus. Endothelium is continuous, with frequent endothelial vesicles, and is largely surrounded by pericyte processes. M, smooth muscle cells. Calibration bar, 5 μm. B: capillary (L, lumen) of subepithelial plexus that underlies basal epithelial cells (E) of forestomach stratified squamous epithelium. Capillary endothelium is continuous with endothelial vesicles and is largely surrounded by pericyte processes. Calibration bar, 5 μm. C: corrosion vascular cast of rat forestomach: view of gastric luminal aspect of cast. Planar array of fine vessels of subepithelial microvascular plexus overlies larger vessels of submucous vascular plexus. A, arteriole; V, venule. Calibration bar, 250 μm. D: corrosion vascular cast of rat forestomach: view of cut edge of cast. Planar array of subepithelial capillaries (SEC) overlies larger submucosal vascular plexus (SM), with capillary network of muscularis externa layer (MEL) below. Calibration bar, 250 μm.

From Browning et al.


Figure 3.

Microvascular organization of oxyntic mucosa (of stomach) and proposed mechanism for microvascular transport of produced by parietal cells toward surface mucous cells in a local portal pattern (inset).

From Gannon et al.


Figure 4.

Electron micrographs of rat gastric microvessels. A: capillary (L, lumen) adjacent to two parietal cells (PC). Note fenestrations in capillary endothelium and close proximity of capillary to parietal cells (open arrowheads). Calibration bar, 2.5 μm. B: higher magnification of capillary close to parietal cells. Note fenestrae with diaphragm and endothelial vesicles in endothelium, separate basal lamina (BL) of capillary and parietal cell, and mitochondria (M) and canaliculi (CN) of parietal cell. Calibration bar, 1.0 μra. C: corrosion microvascular cast of rat gastric corpus after ethanol‐induced ulcer formation; view of luminal aspect. Note loss of patency of capillaries throughout much of mucosal thickness almost to submucosa in center of field, so that submucous vascular plexus is just seen (arrow); complete mucosa at bottom. In eroded area, mucosal venules (arrowheads) are cast, presumably by retrograde filling; several ruptures of microvessels are evident at top, permitting extrusion of plastic. Calibration bar, 500 μm.

A, B from Gannon et al. ; C from O'Brien et al.


Figure 5.

Mucosal microcirculatory patterns typical of human and rabbit small intestine (except duodenum). VA, villus arteriole; VV, villus venule; solid arrows indicate directions of blood flow; open arrows indicate intraluminal flux of succus entericus from crypts to villi.

Adapted from Casley‐Smith and Gannon


Figure 6.

Scanning electron micrographs of villi of small intestine from several species. A: human villi; note variety of villus shapes. Calibration bar, 500 μm. B: dog villi; note stout cylindrical shape. Calibration bar, 250 μm. C: cat villi; note slender fingerlike shape. Calibration bar, 100 μm. D: rat villi; note leaflike flattened shape. Calibration bar, 250 μm.

A from Gannon et al. ; B, C from Gannon et al.


Figure 7.

Models of villus microcirculatory pattern. A: fountain pattern of villus blood flow; B: tuft pattern; C: stepladder pattern; D: combined fountain supply to villus tip and tuft supply to villus shaft, as described by Casley‐Smith and Gannon for rabbit, rat, and human villi. Dotted lines represent watershed region between two blood flow sources to villi (i.e., direct arterial supply to the villus tip and indirect local portal supply via the periglandular capillaries). This watershed level varies in height up the villus with the species.

Adapted from Gannon


Figure 8.

A: montage of in vivo photomicrographs of rabbit intestinal villus (ex video monitor screen), a, Arteriole; v, venule; arrows, principal directions of capillary blood flow; dotted lines, division between villus tip and shaft blood flows, as shown in Fig. and Fig. D. Calibration bar, 250 μm. B: vascular corrosion cast of rat pylorus and proximal duodenum, bisected along duodenal long axis. PY, pylorus; DV, most proximal duodenal villi; L, duodenal lumen; S, duodenal serosa; area outlined with dotted line, compact mass of Brunner's glands. Calibration bar, 1,000 μm.

A from Gannon ; B from Browning and Gannon


Figure 9.

Scanning and transmission electron micrographs of rat small intestinal villi illustrating myofibroblast‐like cells. A: low power of rat villus, with epithelial sheet removed in foreground; note cellular network of myofibroblast or fibroblast‐like cells (*) that overlie the subepithelial capillary plexus (solid arrows). Open arrows indicate goblet cell apices. Calibration bar, 20 μm. B: higher magnification of fibroblast‐like cell (FLC) network that overlies villus capillaries (arrows). Calibration bar, 5 μm. C: Process of fibroblast‐like cell; note prominent bundle of 6‐nm filaments (arrows) and also rough endoplasmic reticulum with distended cisternae (open arrows), which is characteristic of these cells. Calibration bar, 1.0 μm.

A from Desaki et al. a); B courtesy of J. Desaki and Y. Euhara; C courtesy of J. Desaki


Figure 10.

Micrographs of dog intestinal villi. A: cast of dog intestinal villi. Note completely filled villus tip vessels arrayed in fountain pattern. Calibration bar, 500 μm. B: cast of partially filled dog villi with tips not cast. Capillaries of villus lower shaft connect with capillaries of pericryptal plexus, presumably in tuft pattern. Calibration bar, 250 μm. C: transverse section of cast of dog villi at middle third of villus; incomplete cast with tip region not filled. Villus arteriole (A) serially supplies (white arrow) and villus venule (V) serially drains (black arrow) subepithelial capillary network in stepladder pattern. Calibration bar, 100 μm. D: transverse section at midshaft of dog villus, 1 μm plastic section, polychrome stain. A, arteriole; V, venule; CL, central lacteal; black arrows indicate subepithelial capillaries; E, villus epithelium. Calibration bar, 100 μm.

From Casley‐Smith and Gannon


Figure 11.

Scanning electron micrographs of microvascular corrosion casts of small intestinal villi of four mammalian species. A: human villi. Note difference in size between adjacent villi and connection of villus capillaries to capillary rings surrounding intestinal gland openings. A, arteriole; V, venule. Calibration bar, 100 μm. B: rat villi, duodenum. Note broad flattened villi arrayed across long axis of gut. C, capillary plexus of villus; PC, pericryptal plexus surrounding intestinal glands; A, arteriole; V, venule. Calibration bar, 250 μm. C: cat villi. Note slender form; plexus consists solely of capillaries (C) and an arteriole (A) in tuft pattern, as seen in partially filled villus at bottom left; there is no villus venule. Mucosal venules commence at level of villus base between adjacent villi. Calibration bar, 100 μm. D: rabbit villi. Note arteriolar breakup near tip and villus capillaries connected to plexus surrounding intestinal gland openings (arrows). A, arteriole; V, venule. Calibration bar, 250 μm.

A from Gannon ; B from Browning and Gannon ; C, D from Gannon et al.


Figure 12.

A: major vascular supply and drainage routes of Brunner's gland tissue in rat proximal duodenum. Inset, dorsal view of horizontal schematic section of rat stomach, indicating location of Brunner's glands. B: parallel nature of separate circulations of Brunner's glands and of villus tip and shaft in duodenum. Note that presumably acidified blood (after secretion in Brummer's glands) is not supplied to villi, which have to cope with an exogenous H+ load from duodenal lumen (ex gastric juice).

From Browning and Gannon


Figure 13.

Microvasculature of rat colonic mucosa. A: corrosion microvascular cast of rat midcolon. Constricted muscle and local absence of fecal pellet produces constricted lumen (L). Larger vessels of submucous vascular plexus (SM) are evident, but vasculature of muscularis externa is not filled. Calibration bar, 1,000 μm. B: fractured cast of rat colonic mucosa; oblique view of luminal aspect. Capillaries nearest lumen are arranged in honeycomb‐like plexus surrounding openings of colonic glands (*). Site where mucosal venule commences drainage (D) is also identified. Arterioles (A) branch to capillaries only near submucosal aspect. Calibration bar, 250 μm. C: microcirculatory pattern of rat colonic mucosa; pattern is analogous to that observed in rat and human stomach (cf. Fig. ). D: fenestrated capillary of rat/human colonic mucosa. Colonocytes (C) abut epithelial basal lamina (arrow). Calibration bar, 5 μm.

A, B, C from Browning and Gannon


Figure 14.

Blood and lymph microcirculation of intestinal villus, illustrating closeness of fenestrated capillaries to base of mucosal epithelium.

From Granger


Figure 15.

Cross section of blood capillary in intestinal mucosa of mouse. Endothelial layer (en) consists of single cell whose attenuated part faces intestinal epithelium (ep). Thicker part (perikaryon) contains cellular organelles and faces center of villus. Attenuated part contains numerous fenestrae with diaphragms; their aggregate area amounts to ∼5% of endothelial surface. Thicker part of endothelium is provided with flask‐shaped (v1) and apertured (v2) vesicles. bm, Continuous basement membrane; pc, pericyte pseudopodia. X29,000.

From Clementi and Palade


Figure 16.

Continuous and fenestrated capillary walls. 1–4, Plasmalemmal vesicles, interendo‐thelial junctions, vesicle channels, and fenestrations, respectively. Dimensions of different strictures are indicated in angströms. Schematic transendothelial channel is shown at top, illustrating outer dimensions of channel (500 Å), dimensions of strictures within channel (100–400 Å), and selectivity of diaphragms within channel (50–100 Å).

From Taylor and Granger


Figure 17.

Four consecutive sections through inter‐endothelial junction in rat heart capillary. Arrows mark points of contact between junctional membranes. In serial section, each point of contact appears to open to form a patent pathway through junction around points of membrane apposition. L, lumen.

From Bungaard


Figure 18.

Mean dimensions of inter‐endothelial junctions in lung (top) and skeletal muscle (bottom) capillaries in rabbit. To facilitate comparison, widths of junction are shown going from narrowest values (0–5 nm) on luminal side to widest values (>25 nm) on interstitial side, although in reality various widths occur at random along junction. Only a small proportion (5%) of junction is narrowed to width of 0–5 nm, and remainder of junction opens to a width >5 nm.

From Perry
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B. J. Gannon, M. A. Perry. Histoanatomy and ultrastructure of vasculature of alimentary tract. Compr Physiol 2011, Supplement 16: Handbook of Physiology, The Gastrointestinal System, Motility and Circulation: 1301-1334. First published in print 1989. doi: 10.1002/cphy.cp060136