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Vascular network in papillae of dog oral mucosa using corrosive resin casts with scanning electron microscopy.

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THE ANATOMICAL RECORD 226:447-459 ( 1990)
Vascular Network in Papillae of Dog Oral Mucosa
Using Corrosive Resin Casts With Scanning
Electron Microscopy
YOSHIAKI KISHI, KAZUTO TAKAHASHI, AND HENRY TROWBRIDGE
Department of Oral Anatomy, Kanagawa Dental College, Inaoka, Yokosuka, Japan (Y.K.,
K.T.);Department of Pathology, School of Dental Medicine, University of Pennsylvania,
Philadelphia (H.T.)
ABSTRACT
The purpose of this study was t o undertake a three-dimensional
analysis of the vascular network of the lamina propria in the gingiva, alveolar
mucosa, buccal mucosa, palate, and lingual mucosa of the dog. Using the corrosive
resin casting technique, casts of the vascular network were prepared and examined
by scanning electron microscopy.
In the oral mucosa, larger arteries in the submucosa divide into smaller
branches that enter the lamina propria. These branches form one or more layers of
vessels a t the base of the papillae of the lamina propria, the so-called subpapillary
vascular network. Here the vessels divide again and enter the papillae to form a
subepithelial capillary network. The configuration of the capillary loops within
each papilla of the lamina propria is determined by the shape of the papilla. The
characteristic shape of the loops resembles a hairpin. The capillary loops in the
lingual papillae are larger and more complex than capillary loops found elsewhere
in the oral mucosa. The mucosa of the posterior portion of the hard palate, the soft
palate, and the tongue contain many venous valves.
The basic structure of mucous membrane varies in enter the lamina propria and divide to form a subepidifferent areas of the oral cavity in accordance with thelial capillary network in the papillae. Veins arising
functional demands. There are three basic types of oral from the capillary loops follow the course of the arteries.
The tongue consists of a core of connective tissue and
mucous membrane: masticatory mucosa, lining mucosa, and specialized mucosa. Masticatory mucosa sur- skeletal muscle, which is covered by the lingual murounds the teeth and covers the hard palate and is thus cosa. The mucosa consists of a submucosa that overlies
subjected to the major forces of mastication. Hence the the muscle and a lamina propria that is covered by
surface epithelium is keratinized and the lamina pro- epithelium. The anterior portion of the dorsal lingual
pria is thick, dense, and firm. The submucosa of the mucosa contains numerous lingual papillae and taste
gingiva contains coarse collagenous bundles that ex- buds. These lingual papillae are formed by the projectend from the bone to the lamina propria. The submu- tion of small, nipple-shaped elevations of the conneccosa of the hard palate is well defined and tightly tive tissue (i.e., papillae of the lamina propria) into the
bound to the periosteum of the palatal and maxillary overlying epithelium, thus producing evaginations of
the mucous membrane. Five types of lingual papillae
bones.
Lining mucosa of the oral cavity is associated with can be distinguished on the dog tongue: filiform, fungithe lips, cheeks, vestibule, floor of the mouth, under- form, foliate, circumvallate, and conical (lenticular).
surface of the tongue, alveolar process, and soft palate. Each type has its own characteristic microvasculature.
It is generally recognized that the blood supply to the
The surface epithelium of this type of mucosa is relatively thick and unkeratinized, and the lamina propria tongue is more plentiful than to most other tissues of
is thinner and less dense than that of the masticatory the body (Hellekant, 1971). The upper surface of the
mucosa. Specialized mucosa is found on the dorsum of tongue receives its blood supply from the vertical
branches of the profound lingual artery, which is a conthe tongue and contains taste buds.
The lamina propria of mucous membrane contains tinuation of the lingual artery. Together with branches
papillae that indent the overlying epithelium. These from the dorsal artery, the vertical branches of the propapillae contain capillaries as well as nerve fibers.
They vary in length and width in different regions of
the oral mucosa. While in the gingiva the papillae are
characteristically tall and slender, papillae of the alveReceived September 6, 1988; accepted July 18, 1989.
olar mucosa, hard and soft palates, and buccal mucosa
Address reprint requests to Henry Trowbridge, Ph.D., Department
are low in height.
of Pathology, School of Dental Medicine, University of Pennsylvania,
Tributaries of the larger arteries in the submucosa Philadelphia, PA 19104-6002.
0 1990 WILEY-LISS, INC.
448
Y. KISHI ET AL.
Figs. 1-4.
VASCULAR NETWORK OF ORAL MUCOSA
449
Fig. 5. Sagittal section of the vascular network of buccal mucosa. a,
arteriole; v, venule; spcn, subpapillary capillary network; M, muscle.
Bar = 100 pm.
Fig. 7. External view of the vascular architecture of buccal mucosa.
Note relatively high density of capillary loops. Star indicates orifice of
minor salivary gland duct. Bar = 100 pm.
Fig, 6. Resin cast shown in Figure 5 as seen from the opposite side.
a, arteriole; v, venule; spcn, subpapillary capillary network. Bar =
100 pm.
Fig. 8. Capillaries of buccal mucosa showing simple loops. a, ascending limb of capillary loop; v, descending limb of loop. Bar = 100 pm.
Fig. 1. Vascular network, gingiva, showing distribution of venules
(V) and arterioles (A) in lamina propria. Cr, location of tooth crown.
Bar = 1,000 pm.
Fig. 2. Vascular network in the lamina propria of the marginal
(free) gingiva. The capillary bed consists of characteristic capillary
loops that resemble a hairpin. a, ascending limbs of capillary loops; v,
descending limbs of loops; Cr, tooth crown. Bar = 100 pm.
Fig. 3. External view of the vascular architecture of the gingiva (G)
and alveolar mucosa (AM). MGJ, mucogingival junction. Bar = 1,000
pm.
Fig. 4. Relatively short capillary loops in papillae of alveolar mucosa. a, ascending limb of capillary loop; v, descending limb of loop.
Bar = 100 pm.
found lingual artery form two vascular plexuses, a submucosal plexus and a subpapillary plexus. The capillary network of the lingual papillae is derived from
branches of the subpapillary plexus.
The vascular network of the submucosa and lamina
propria of the oral mucosa has received considerable
attention in the literature. The vascular anatomy of
the gingiva has been examined by Forsslund (19591,
Egelberg (19661, Hock and Nuki (1971), Kindlova
(1965), Kishi and Takahashi (19781, and Kishi (1982),
whereas Klotz (1887), Schafer (19291, and Swindle and
Maher (1963) studied the blood vessels of the palate.
Earlier studies utilizing the microarteriographic technique developed by Takahashi (1962a,b) provided a
Y. KISHI ET AL.
450
Fig. 9. Capillary loops encircling the orifice (star) of buccal salivary
gland duct. Bar = 100 pm.
Fig. 10. Vascular network of parotid papilla. Numerous capillary
loops form concentric rings around the orifice (star) of the parotid
gland duct. Bar = 100pm.
general description of the microvasculature of the lingual papillae.
In this paper we present the results of a three-dimensional analysis of the vascular network in the papillae
of dog oral mucous membrane. Vascular casts of the
microvasculature of the gingiva, alveolar mucosa, buccal mucosa, hard and soft palate, and tongue were prepared and examined by scanning electron microscopy
Immediately following fixation, the tongue was resected and cannulas were inserted into the right and
left lingual arteries. Mercox was injected into the cannulas under pressure to perfuse the vascular bed. After
the resin had polymerized, the tissue was digested with
10%potassium hydroxide, leaving only the resin cast of
the vascular network.
All of the specimens were washed thoroughly with
40°C tap water and freeze-dried. After being coated
with platinum-palladium, the specimens were examined under SEM.
(SEM).
MATERIALS AND METHODS
Two adult mongrel dogs were anesthetized with sodium pentobarbital(25 mg/kg). The left and right common carotid arteries were cannulated, and Ringer’s saline solution was then perfused into the arteries until
the jugular veins were cleared of blood. Glutaraldehyde
(2%) in phosphate buffer (pH 7.4) was immediately injected into the carotid arteries to provide fixation of the
vessels and their tributaries.
Following fixation, cannulas were tied to the left and
right external carotid arteries. A freshly prepared solution of a low viscosity resin (Mercox) was then injected under pressure from a specially designed syringe
into the cannulas. After the resin had hardened, the
jaws were removed and decalcified in 10% nitric acid
for several days. The demineralized tissues were then
macerated in a 10% solution of potassium hydroxide
until only the resin casts of blood vessels remained.
In some cases the teeth and mandible were not demineralized so that the spatial relationship between the
vascular casts and the mineralized tissues could be assessed. These specimens were frozen as soon as the
resin had hardened and cut into small blocks. The soft
tissues were digested away by incubating the blocks a t
40°C for approximately 2 weeks in a phosphate-buffered solution (pH 8.4) containing proteinase a t a concentration of 20%.The buffer solution was changed every other day to prevent it from becoming acidic.
RESULTS
In the oral mucosa larger vessels in the submucosa
divide into smaller branches that enter the lamina propria. The branches form one or more layers of vessels at
the base of the papillae of the lamina propria, thus
forming the subpapillary vascular plexus. The number
of layers of vessels in this plexus varies from one area
of the mucosa to another. The vascular network of the
Fig. 11. Occlusal view of venous plexus (V) of the lamina propria
of hard palate. Arterioles (A) can been seen running through transverse palatine ridges. Bar = 1,000 pm.
Fig. 12. Venous valve in the venous plexus of hard palate. Asterisks
indicate valve sinusoids. The arrow shows direction of blood flow. Bar
= 100 pm.
Fig. 13. External view of capillary network in papillae of mucosa of
hard palate. Note well-developed transverse palatine ridges. Cr, location of tooth crown; G, capillary loops of gingiva. Bar = 1,000 pm.
Fig. 14. High magnification of inset in Figure 13 demonstrating
simple capillary loops. a, arterioles; v, venules. Bar = 10 pm.
Fig. 15. High magnification of inset in Figure 13 showing anastomosing capillary loops in the crest of a transverse palatine ridge. a,
ascending portion of capillary loop; v, descending portion of capillary
loop. Bar = 10 pm.
VASCULAR NETWORK OF ORAL MUCOSA
Figs. 11-1 5.
451
452
Y. KISHI ET AL.
Figs. 16 and 17.
453
VASCULAR NETWORK OF ORAL MUCOSA
Fig. 18. Cast of capillary network in the superficial layer of the lamina propria of the dorsum of the
tongue. Note numerous corolla-shaped capillary loops distributed in the filiform papillae (FP). The
subpapillary network (spcn) interconnects the vessels of the papillae. Bar = 100 pm.
papillae of the lamina propria consists primarily of capillary loops whose characteristic shape resembles a
hairpin or horseshoe.
Gingiva
Examination of the vascular casts revealed that the
blood supply of the gingiva is derived chiefly from
branches of arteries that run along the outer surface of
the alveolar bone. These vessels anastomose with
branches of arteries from the periodontal ligament as
well as with arteries t h a t emerge from the crest of the
alveolar bone.
The arteries that ascended along the surface of the
alveolar bone cross the alveolar ridge, enter the gingiva, and then follow a course 700-800 pm below the
outer surface of the gingiva. These arteries give off
numerous branches that extend through the submucosa to form the vascular network of the lamina propria
(Fig. 1).
Measurements of vascular dimensions in the lamina
propria beneath the papillae revealed that the diameter of casts of the arterioles ranged from 15 to 20 pm,
Fig. 16. Occlusal view of the capillary network beneath soft palate
mucosa. Interconnecting capillary loops encircle the orifice of excretory duct of palatine gland (asterisks). Bar = 100 pm.
Fig. 17. High magnification of inset in Figure 16. Anastomosing
capillary loops encircling the orifice of palatine gland duct (asterisk).
a, arterioles; v, venules. Bar = 100 pm.
whereas casts of the venules were considerably larger,
having diameters ranging from 44 to 55 pm. Branches
arising from this network form yet another layer of
vessels a t the base of the papillae, the so-called subpapillary vascular network. The diameter of the casts
of arterioles and venules that comprise this network
was approximately 12 and 20 pm, respectively.
Capillary loops in the gingival papillae consist of a n
ascending arterial limb and a descending venular limb.
The diameter of the descending portion of the loops is
generally greater than that of the ascending portion
(Fig. 2).
Gingiva is divided into free gingiva and attached
gingiva. The free gingival groove represents the transition zone between the free and attached gingiva.
Characteristically the capillary loops in the papillae of
free gingiva are the tallest of any of the capillary loops
observed in various areas of the oral mucosa. In passing from the free gingiva through the transition zone to
the attached gingiva, the capillary loops in the papillae
become shorter and there is less space between the arterial and venular ends of the loops. No differences
were noted in the subpapillary network in the free and
attached gingiva.
Alveolar Mucosa
The gingiva is separated from the alveolar mucosa
by a scalloped line, the mucogingival junction. While
the gingiva is tightly bound to the underlying periosteum, the alveolar mucosa covers the outer surface of
Y. KISHI ET AL.
454
Fig. 19. High magnification of filiform papilla. Capillary loops in primary papilla (I),secondary papilla
(II), and tertiary papilla (111). a, ascending limb of capillary loop; v, venule; SPCN, subpapillary capillary
network. Bar
=
100 pm.
Fig. 20. Vascular network in fungiform papilla. a, ascending limb of capillary loop; d, descending limb.
Bar = 100 wm.
the alveolar process and is loosely attached to the periosteum.
The vascular network of the lamina propria of the
alveolar mucosa was similar to that in the gingiva.
However, the capillary network beneath the mucosa
has a greater density and a different morphological
arrangement than in the gingiva (Fig. 3).
Capillary loops in the papillae of the alveolar mucosa
are quite short compared with the papillae of the gingiva. They are arranged in a continuous wave-like pattern with juxtaposed rows of capillary loops running
parallel to the mucogingival junction (Fig. 4).
Buccal Mucosa
The lamina propria of the mucosa on the cheek (buccal mucosa) consists of dense connective tissue that extends short papillae into the overlying epithelium. In
general, the vascular network is less extensive than in
gingiva. Examination of casts of vessels in the lamina
propria revealed a network in which arterioles and
venules run closely together (Figs. 5, 6). O'ften two
venules run together with a single arteriole. This ar-
rangement does not occur in the lamina propria of other
oral mucous membranes. The diameter of the casts of
the arterioles measured approximately 20 Fm, whereas
many of the venules were nearly 40 pm in diameter.
Thus these arterioles and venules are comparable in
size t o those in the lamina propria of the gingiva.
The capillaries in the papillae form typical hairpin
loops that are simple and short in height. There is little
difference in the diameters of the ascending and descending limbs of the loops (Figs. 7 , 8).
Fig. 21. Capillary loops in fungiform papilla. a, ascending limb of
capillary loop; d, descending loop. Bar = 100 pm.
Fig. 22. Vascular network in folliate papilla (FP). By dissecting
away the overlying superficial capillary network, a large venule (V)
can be visualized. Bar = 1,000 pm.
Fig. 23. High magnification of a portion of the vascular network in
a folliate papilla. V, large venule; a, arteriole; v, small venule. Bar =
100 Km.
Fig. 24. Vascular network of conical papilla. Asterisks indicate
unique corolla-like capillary loops; d, descending venule. Bar = 100
pm.
VASCULAR NETWORK OF ORAL MUCOSA
Figs. 21-24.
455
456
Y. KISHI ET AL.
Fig.25.
457
VASCULAR NETWORK O F ORAL MUCOSA
Numerous minor salivary glands are located beneath
the buccal mucosa. In general, capillary loops associated with the ducts of these glands are organized in a
corolla-like pattern that surrounds the orifices of the
ducts (Fig. 9).
Figure 10 depicts capillary loops in the parotid papilla that surrounds the orifice of the excretory duct of
the parotid gland. Numerous tall capillary loops are
observed, forming several concentric rings around the
orifice of the duct.
Palate
In the lamina propria of the hard palate and soft
palate, three or four layers of veins form a well-developed venous plexus 100-800 pm in diameter (Fig. 11).
Figure 12 depicts one of the numerous venous valves
that are found in this plexus.
In the dog palate, many transverse palatine ridges
are distributed over almost the entire length of the
hard palate. The capillary loops in the papillae of these
ridges form regular rows that are aligned at a right
angle to the curved ridges, a s shown in Figure 13. Most
of the capillaries in the palatine ridges take the shape
of simple hairpin loops (Fig. 14). However, in the crest
of the ridges, the capillaries form complex loops with
many anastomoses (Fig. 15).
As compared with the hard palate, the mucous membrane of the soft palate is more highly vascularized and
the papillae of the lamina propria are shorter and
fewer in number. As in the hard palate, the capillary
loops in the papillae are aligned in parallel rows that
extend from the gingival region of the palate to the
palatine raphe. The morphology of these capillary
loops, as shown in Figure 16, is similar to those of the
buccal mucosa (Fig. 8) and hard palate (Fig. 14).
Many excretory ducts of palatine glands open onto
the soft palate. Capillary loops encircle the orifice of
these ducts and form complex anastomoses in a corollalike network (Fig. 17).
Dorsal Lingual Mucosa
In describing the vasculature of the lingual papillae,
one is faced with a problem of terminology. Each lingual papilla is covered by epithelium and contains a
core of connective tissue, the papillae of the lamina
propria. In this paper the term papilla is used to denote
the lingual papillae as well a s the connective tissue
papilla that they contain.
Examination of the vascular casts revealed that, in
the dorsal lingual mucosa, branches from arteries and
veins in the submucosa enter the lamina propria and
form a subpapillary vascular network. From this network capillaries extend into the papillae. The subpapillary network consists of two layers of vessels. By removing the capillary loops in the papillae, the two
layers of vessels could be visualized.
The vascular network just beneath the papillae is
composed of small arterioles and venules. The second
Fig. 25. External view of vascular network in a vallate papilla (VP)
and encircling ridge (large white arrow). Arrowheads, capillary loops
in secondary papilla (11); asterisks, unvascularized area. Bar = 100
wn.
layer, located just beneath the first layer, is composed
of larger venules and arterioles. The casts of the largest
of these venules had a diameter of 160 km, whereas the
diameters of casts of the arterioles reached a maximum
of 50 km. Many descending limbs from capillary loops
in the papillae drain into the larger venules in this
layer.
Capillary loops are distributed throughout the papillae within the lingual papillae, as shown in Figure 18.
The capillary loops in the individual papillae are connected to capillary loops in adjacent papillae by a subpapillary capillary network (SPCN) consisting of a single layer of capillaries running just beneath the
epithelium.
Filiform Papillae
Of the lingual papillae, the filiform papillae are the
most numerous. They are located on the rostrodorsal
two-thirds of the tongue and consist of cone-shaped,
fine, pointed structures composed of a core of connective tissue that carries secondary and tertiary papillae
having the appearance of coiled loops. Capillary loops
were found only in the primary papillae.
In general, the capillary loops in the filiform papillae
are arranged radially beneath the surface epithelium
in a corolla-like pattern, with the largest primary capillary loop always near the lingual side of the papilla,
a s shown in Figure 19. The primary capillary loop is
surrounded by one to two secondary loops and three to
five tertiary loops located on each side of the papilla.
In the primary capillary loops, several ascending
limbs follow a course toward the filiform papilla, then
branch off and anastomose with adjacent ascending
and descending loops, finally converging into a large
descending limb that appears to drain directly into one
of the small venules of the outer vascular layer of
the subpapillary vascular network. Tertiary capillary
loops are formed of one ascending limb (an arterial
capillary) and one descending limb (a venular capillary). These loops conform to a very simple hairpin
pattern. In contrast to this, secondary capillary loops
are found to be intermediate in type between primary
and tertiary loops. These loops form fewer anastomoses
than do the primary loops.
Fungiform Papillae
Mushroom-shaped fungiform papillae are interspersed among the filiform papillae. Taste buds are present
on the dorsal surface of these papillae. Because of their
rich capillary network, these papillae appear as reddish prominences.
The capillary loops of the fungiform papillae conform
to the mushroom shape of the papillae. The capillaries
entering the base of each papilla are arranged radially
and contain many complex anastomoses. Several ascending limbs of these capillaries form short, hairpin
loops in the superficial portion of the connective tissue
papilla, a s shown in Figures 20 and 21. Immediately
subjacent to this capillary network, the ascending roots
converge into a few descending limbs, pass downward
to the base of the papilla, and then drain into small
venules in the subpapillary vascular network.
458
Y. KISHI ET AL.
Foliate Papillae
The foliate papillae are mucosal folds that occur on
the dorsolateral margins of the tongue, rostral to the
palatoglossal arch. These papillae are also associated
with taste receptors. There are 8 to 12 foliate papillae
that consist of parallel clefts that are bounded by narrow folds of the mucous membrane. Each papilla appears long and slender and is aligned at a right angle
to the dorsal surface of the tongue (Fig. 22).
Figure 23 depicts a portion of the vascular network
in a foliate papilla. Within the network can be seen a
large venule 100-120 pm in diameter and a n arteriole
35-40 pm in diameter. The arteriole follows a course
that is parallel to, and just beneath, the epithelia1 lining of the foliate papilla. Capillary branches enter the
papilla and form either a flat capillary network, with a
meshwork approximately 50 pm in diameter, or small
hairpin loops that extend into the superficial layer of
the papilla. These capillaries anastomose with each
other and converge into a large venule such a s the one
shown in Figures 22 and 23. Between foliate papillae,
the SPCN is similar to the capillary network within
the papilla. However, neither arterioles nor venules
could be identified beneath the SPCN between the papillae.
avascular areas could be observed among these capillaries. On the sides of these avascular areas, capillaries
are arranged in a flat network. Encircling each vallate
papilla are one or two vascular prominences, the outer
layers of which are formed either by a flat capillary
network or by small hairpin loops.
DISCUSSION
The corrosive resin cast technique provides a n ideal
method for studying three-dimensional images of the
microvascular network of tissues. As compared with
other vascular perfusion methods, this technique offers
several advantages. The ability to obtain imprints of
the walls of small blood vessels makes it possible to
differentiate between arterioles and venules. Thus, in
the walls of arterioles, the resin cast impressions of
endothelial cells are spindle-shaped whereas in venules they have a hexagonal appearance (Kish e t al.,
1988).
In this study the resin cast method used in previous
investigations was modified and improved by injecting
Mercox into vessels that had first been fixed with glutaraldehyde. In this way we were better able to preserve the walls of blood vessels and prevent the extravasation of resin. The use of a fixative is also
designed to minimize the expansion of vessels during
Conical Papillae
injection of the resin, thus making it possible to obtain
In the dog, the conical papillae are distributed in the accurate estimates of the size of vessels.
caudal portion of the tongue. They are the tallest of the
Our results indicate that in the dog oral mucosa the
lingual papillae and are shaped like a double convex configuration of capillary loops within each papilla is
lense.
determined by the shape of the papilla. In general, the
Several arterioles pass upward from the mucosa and shape of the capillary loops in the papillae of gingiva,
enter each papilla. These branch to form a capillary buccal mucosa, and hard and soft palate resembles a
network in the superficial layer of the papilla. The hairpin. This is in agreement with the results of a prelower half of this network is flat while the upper half is vious study on the capillary system in the gingiva
composed of many short hairpin loops (Fig. 24). A well- (Forsslund, 1959). Capillaries encircling the orifices of
developed venular limb is situated in the deep layer of both small and large salivary glands form complex
this capillary network. Many venules are arranged loops that anastomose with each other to form a coaround the center of the papilla. These anastomose and rolla-like pattern. (Figs. 13, 14, 21).
finally converge into a large descending venule, the
The form of the subpapillary vacular network located
diameter of which measures 100 pm, where it reaches in the base of the papillae of the lamina propria was
the base of the connective tissue papilla. Several small consistent in the various tissues examined. However,
corolla-shaped capillary loops arise from near the base differences were noted in the density and extent of the
of the papilla. These are similar in appearance to the vascular network. Thus the venous plexus was more
capillary network encircling the orifice of the excretory highly developed in the masticatory mucosa of the hard
ducts of small salivary glands in the buccal mucosa.
palate and gingiva than in the other areas of the oral
mucosa.
Vallafe Papillae
Venous valves were observed only in the lamina proThe vallate papillae, four to six in number, are the pria of the hard and soft palate and tongue. The preslargest of the lingual papillae. They are arranged in a ence of venous valves in the tongue has not been preV shape on the dorsal surface of the tongue and demar- viously reported. Klotz (1887) expressed the view that
cate the junction of the rostral two-thirds and caudal it is not possible to visualize venous valves with diamone-third of the tongue. Each papilla is bounded by a eters that are less than 1 mm. More recently, Todo
(1950) reported finding mesenteric venous valves havdeep circular furrow, the vallate papilla moat.
In the lamina propria a t the base of each of the val- ing a diameter of only 40-200 pm. The casts of many of
late papillae a n arteriole and venule run together the venous valves observed in the present investigation
along a n annular course that follows the profile of the were considerably less than 1 mm in diameter (Fig. 12).
In the palate the presence of venous valves may propapilla and circular ridge. From these vessels many
branches pass into both the papilla and the ridge, thus vide a mechanism to prevent blood from being forced in
forming a characteristic vascular network. Many small a direction away from the heart when strong masticatufts of hairpin-shaped capillary loops are arranged on tory forces compress the mucosa. High pressures may
the superficial portion of each papilla (Fig. 25). Slightly also be created during movements of the tongue, and it
larger capillary loops were observed in the secondary is likely that the venous valves help to control blood
papillae on the dorsal surface of the papilla. Several flow by allowing blood to move in only one direction.
VASCULAR NETWORK O F ORAL MUCOSA
LITERATURE CITED
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using, papilla, vascular, network, resins, electro, mucosal, corrosive, cast, microscopy, scanning, oral, dog
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