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The fine structure of bone in the nasal turbinates of young pigs.

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The Fine Structure of Bone in the Nasal
Turbinates of Young Pigs
Department of Veterinary Pathology, The Ohio State University,
Columbus, Ohio 43210
The three types of bone cells in the nasal turbinates had characteristic ultrastructural features. Osteoblasts were located in areas of new bone
formation and had abundant endoplasmic reticulum, prominent Golgi apparatuses, numerous vesicles, and cytoplasmic processes that penetrated the adjacent osteoid. Osteocytes had variable ultrastructural characteristics. The predominant cell filled the lacuna, had few organelles, smooth plasma membranes,
and was interpreted to be a mature resting osteocyte. Some osteocytes appeared
to be transitional between osteoblasts and mature osteocytes. Evidence of matrix
formation was seen near osteocytes with well developed organelles, whereas
osteocytes with swollen mitochondria, dense bodies and irregular plasma membranes appeared to be involved with resorption of bone. Multinucleated osteoclasts contained numerous mitochondria and had crystals or unmineralized
collagen fibrils between folds and within vacuoles of the cytoplasmic projections
forming the brush border.
Electron microscopy has contributed to- ing an ability to synthesize abundant proward an understanding of the functional tein. Osetocytes resembled osteoblasts and
cytology of bone cells and their relationship also had the capacity to form collagen, but
to the organic matrix and mineral phase their role in bone resorption was equivocal.
of bone. Early investigators evaluated bone Osteoclasts had features which suggested
matrix rather than the cells involved in its their function was to destroy bone.
Although marked pathologic alterations
formation (Wolpers, '49; Robinson, '52;
Robinson and Cameron, '57; Molnar, '59). occur in the nasal turbinates in man and
The first detailed descriptions of the fine swine with atrophic rhinitis, the fine strucstructure of bone cells in chick embryos ture of turbinate bone has not been estab(Jackson and Randall, '56) and kittens lished. Therefore, the specific objective of
(Scott and Pease, '56) were followed this investigation was to evaluate the ultrarapidly by observations in rats (Ascenzi structure of tubular cancellous bone in the
and Benedetti, '59; Cameron, '61), pigeons ventral nasal turbinates of normal, rapidly
and ducks (Ascenzi et al., '63), and man growing pigs to serve as a basis for sub(Dudley and Spiro, '61). The ultrastructu- sequent investigations on pathologic alterral evaluation of adult cortical bone has ations in bone cells of pigs with experibeen limited (Baud and Dupont, '62; mental and naturally occurring atrophic
Cooper et al., '66) while the fine structure rhinitis (Fetter and Capen, '71a).
of bone in embryonic, postfetal, and neoMATERIALS AND METHODS
natal animals has been investigated in
One litter (6 males, 5 females) of clinigreater detail (Cameron et al., '64; Robinson and Cameron, '64; Anderson and cally healthy Yorkshire pigs served as the
basis for this investigation. They were
Parker, '68).
Recently, Cameron ('69) related the fine creep fed a diet which contained 6.6%
structure of bone cells to what is presently total ash, 1.1% calcium, and 0.8% phosknown of their function. Osteoblasts were phorus beginning at two days of age and
shown to belong to the class of fibrogenic as the only diet following weaning at four
cells with ultrastructural evidence suggestReceived Nov. 9, '70. Accepted Feb. 18, '71.
ANAT. REC., 171: 329-346.
weeks of age. Blood samples were collected
at weekly intervals and at the time of necropsy. The mean serum concentrations of
calcium, phosphorus, and alkaline phosphatase were within the normal range for
rapidly growing pigs at each collection
period. The mean serum concentration of
calcium ranged from 11.1 mg/100 ml at
1 week to 12.5 mg/100 ml in pigs 3.5
months of age. A pig was killed by electrocution at 6, 10, 17, 24, 31, 38, 45, and 59
days of age. The three remaining pigs were
necropsied at 101 days of age.
Sections of the ventral nasal turbinates
were taken at the level of the first premolar
teeth. Multiple sections of the tubular cancellous bone were collected for electron
microscopic evaluation after removal of
the mucous membrane. The bone was cut
into 1.0 mm X 1.0 cm sections, fixed in 3%
glutaraldehyde with sodium cacodylate buffer, and post-fixed in 1 % osmium tetroxide
(Hopps and Strano, '68). Following fixation the tissues were dehydrated through
ascending concentrations of ethyl alcohol,
transferred to propylene oxide, and embedded in maraglas or Epon 812 (Shell
Chemical Corp., San Francisco, California).
Toluidine blue-stained, 1 p thick sections
were examined by light microscopy to select the area of the block to be sectioned.
Thin sections were cut with a diamond
knife at approximately 500 A with a PorterBlum ultramicrotome, floated on a water
bath with the pH above 7.0 to prevent demineralization of the bone, and mounted
on 75 X 300-, 200-, and 400-mesh copper
grids. The sections were stained with
uranyl acetate and lead hydroxide, and examined with a Philips 200 electron microscope. The magnifications listed for the
electron micrographs represent the final
magnifications after printing.
The macroscopic and microscopic characteristics of the ventral nasal turbinates
in pigs have been described previously
(Fetter and Capen, '68; '71b). The ventral
nasal turbinates were evaluated by light
inicroscopy in each pig for characterizatioiz
of the normal structure and to establish the
absence of lesions. In order to assess ossification of turbinate bone, pigs from another litter were evaluated at the critical
periods of birth and three days of age. A
complete necropsy was performed on all
pigs. Representative tissues from all organ
systems were fixed in 10% buffered formalin and examined microscopically. All
paraffin-embedded bone sections were
stained with hematoxylin and eosin, toluidine blue, Heidenhain aniline blue, and
the periodic acid-Schiff reaction. The dorsal
and ventral turbinates were uniform in
size and shape, bilaterally symmetrical,
and had well developed osseous cores and
no evidence of inflammation in the overlying mucous membrane. There were no
lesions in the rest of the skeleton or other
organs of the 15 pigs.
Light microscopy
The ventral nasal turbinate in the pig
was composed of a superior and inferior
scroll attached to the wall of the nasal cavity by a single lateral process situated midway between the two scrolls. The structural
integrity of the scrolls was maintained by
a core of tubular cancellous bone. The osseous core was cartilaginous at birth, but
rapidly underwent perichondral invasion
and ossification so that only small islands
of hypertrophic chondrocytes remained at
10-14 days of age. Endochondral ossification was complete in all pigs by two weeks
of age, and formed numerous trabeculae of
woven bone. The primary woven bone
underwent progressive remodeling to lamellar bone as the pigs increased in age.
The trabeculae were lined by one to three
layers of osteoblasts and osteoprogenitor
cells. Multinucleated osteoclasts were seen
occasionally aligned along the trabecular
surf aces, of ten with an irregular concavity
in the underlying bone. Osteocytes of varying size and shape within lacunae were
dispersed randomly throughout the trabeculae of bone. The periosteal zone consisted of several layers of elongated cells
similar to fibroblasts except on the inner
surface where they were larger and had a
more basophilic cytoplasm.
Electron microscopy
Chondrocytes. The hypertrophic chondrocyte was the only cartilage cell observed
ultrastructurally in the turbinates and occurred in pigs six days to two weeks of
age (fig. 1 ) . They occurred individually or
in nests of two to four cells surrounded by
calcified matrix, invading osteoblasts, osteoid, and trabeculae of woven bone. The
hypertrophic chondrocytes were large,
round or cuboidal, and had numerous irregular cytoplasmic projections extending
from the surface. The cytoplasmic matrix
was relatively electron-translucent and the
organelles concerned with synthesis of
matrix were dispersed throughout the cytoplasm. The endoplasmic reticulum consisted of individual flattened sacs of granular membranes and contained material of
greater density than the surrounding cytoplasm. Aggregates of ribosomes were dispersed throughout the cytoplasm. The
Golgi apparatus occurred in a perinuclear
location and was composed of flattened
agranular membranes associated with
small vesicles. Mitochondria were small
and distributed randomly. Cytoplasmic filaments and lipid droplets were observed
The matrix surrounding the hypertrophic chondrocytes consisted of an interlacing network of fine collagen fibrils in
finely granular, dense ground substance
(fig. 1). Scattered foci of mineralization
were observed throughout the cartilaginous
matrix. Chondrocytes in more advanced
stages of degeneration exhibited regression
of organelles, accumulations of lipid, disintegration of the plasma membrane, and
had cytoplasmic fragments within the
Osteoblasts. The osteoblasts appeared
as plump, elongated cells situated with
their long axes parallel to the trabeculae of
woven bone (fig. 2). They were separated
from the bone by a relatively wide zone of
osteoid in which initial loci of mineralization and nodules of bone were distributed
randomly. The surface of the osteoblast
adjacent to the bone matrix often had cytoplasmic processes which penetrated between the adjacent collagen fibrils of the
osteoid (fig. 2). These projections were
less frequent on the opposite surface of
the osteoblast except in areas where osteoid
was deposited around the entire cell.
Osteoblasts often were closely packed
along bone trabeculae. The plasma membranes of opposing cell surfaces were intact and were usually separated by extra-
cellular spaces of variable widths (fig. 3).
Occasionally, desmosomal structures and
uncomplicated interdigit ations of adjacent
plasma membranes were present. The
plasma membrane of osteoblasts was not
dways well defined, especially on surfaces
adjacent to bone. The surface of osteoblasts
often reflected around a bundle of collagen.
The organelles concerned with protein
synthesis were well developed in osteoblasts. The most striking characteristic of
the cytoplasm was the extensive network
of endoplasmic reticulum (figs. 2, 3 ) . Some
granular membranes were flattened and in
parallel array while others were irregularly
dilated (fig. 3). The luminal contents of the
endoplasmic reticulum were fibrillar or
granular and slightly more dense than the
background cytoplasm. Numerous ribosomes were either attached to the endoplasmic reticulum or dispersed throughout
the cytoplasm and aggregated into rosettes.
Intracytoplasmic bundles of closely packed,
small fibrils were in close proximity to the
outer surface of the endoplasmic reticulum
(fig. 4). They were most prominent near
the plasma membrane adjacent to a layer
of osteoid and extended into the cytoplasmic processes.
A prominent Golgi apparatus was present in the perinuclear location and composed of agranular membranes associated
with numerous vesicles (figs. 2, 3 ) . The
distended Golgi cisternae contained a fibrillar material, similar in appearance to that
observed in dilated sacs of endoplasmic
reticulum. Rough-surfaced vesicles with a
dense limiting membrane were observed in
close proximity to the plasma membrane
(fig. 5). Indentations in the plasma membrane were of similar structure and contained a finely granular material of moderate density. A few large membrane-limited
dense granules, multivesicular bodies and
lysosome-like structures were present in
some osteoblasts (figs. 2, 3, 5).
Mitochondria with prominent cristae
were present throughout the cytoplasm of
osteoblasts (figs. 2, 3 , 4). The outer mitochondrial membrane and the adjacent
granular endoplasmic reticulum often were
in close apposition. Small, dense granules
in the form of rosettes were observed in
certain mitochondria of osteoblasts (fig. 4).
The granules were either in contact with
the inner mitochondria1 membrane or between cristae.
A narrow zone relatively free of organelles was observed infrequently in the cortical cytoplasm of osteoblasts immediately
beneath the plasma membrane (fig. 2).
The only organelles consistently present in
this “cortical zone” were rough-surfaced
vesicles. The majority of the osteoblasts in
the nasal turbinates of pigs contained
organelles, particularly endoplasmic reticulum, in close association with the plasma
membrane (fig. 3 ).
Osteocytes. Osteocytes occurred in various stages of transition between the osteoblasts, from which they develop, and mature osteocytes. Immature osteocytes
closely resembled osteoblasts with respect
to the number and distribution of cytoplasmic organelles (fig. 6). They were not as
elongate as osteoblasts and initially were
surrounded by osteoid with numerous nucleation sites and bone nodules (fig. 6).
Cytoplasmic processes extended from the
surface into the osteoid and mineralized
Osteocytes were smaller, more round in
profile, and had fewer organelles when
they were surrounded by mineralized matrix. Those cells located superficially in
bone trabeculae did not fill the lacunae
completely and the surrounding space was
densely packed with collagen fibers (fig. 7).
Initial loci of mineralization and nodules of
bone occurred in the surrounding osteoid.
Mature osteocytes filled the lacunae but
were separated from their walls by a layer
of amorphous material of moderate density
and loosely arranged collagen fibrils. The
surfaces of the lacunae were relatively
smooth and contained canaliculi through
which cytoplasmic processes extended into
the mineralized matrix (fig. 7). The endoplasmic reticulum was poorly developed
and consisted of small irregularly dilated
cisternae. The Golgi apparatus was composed of flattened lamellae associated with
clusters of small vesicles. Rough-surf aced
vesicles were present near the plasma
membrane (fig. 7). Mitochondria contained
small dense granules similar to those in
osteoblasts. Dense bodies, lipid droplets,
membrane-limited granules, and cytoplasmic filaments were present in some osteocytes.
Osteocytes were present occasionally in
lacunae with irregular and dense surfaces
(fig. 8). The perilacunar matrix appeared
more translucent than the surrounding
bone. The space between the surface of the
osteocyte and the lacunar wall was widened
and contained a prominent band of finely
granular material of moderate density and
loose collagen fibrils. The plasma membrane was irregular and had numerous
pinocytotic vesicles or rough-surf aced indentations. The Golgi and endoplasmic
reticular cisternae were distended and contained moderately dense material. Mitochondrial granules, swollen mitochondria,
and dense bodies were observed frequently
in this type of osteocyte.
Osteoclasts. Osteoclasts appeared as
large multinucleated cells with a dense
cytoplasmic background, located in close
proximity to bone surfaces (fig. 9). The
nuclei were located in an area of the cell
opposite the surface of the bone trabeculae.
The plasma membrane had numerous projections from all surfaces, but particularly
that portion adjacent to bone which had a
complex of folds and finger-like projections
forming the specialized brush border. The
mineralized matrix appeared to be altered
and less dense in the area beneath the
brush border, even with osteoclasts not
applied directly to the bone surface.
The organelles of osteoclasts differed
from those in other bone cells. A striking
feature was the numerous mitochondria of
variable shape distributed throughout the
cytoplasm, except for the area beneath the
brush border (fig. 9). Electron-dense granules were present in many mitochondria.
Another prominent characteristic was the
numerous smooth-surf aced vacuoles and
vesicles in the vicinity of the brush border.
The endoplasmic reticulum was poorly developed but a prominent Golgi apparatus
was present near each nucleus. Centrioles
were observed frequently in the region of
the Golgi apparatus. The background cytoplasm was dense due to numerous free
ribosomes. Rough-surf aced vesicles similar
to those in osteoblasts and osteocytes were
present throughout the cytoplasm. Membrane-limited dense granules were numerous and appeared to fuse with the cytoplasmic vacuoles. Osteoclasts were observed
rarely with other degenerative cells included in their cytoplasm.
The majority of osteoclasts were in juxtaposition to a concavity in the bone surface. The brush border was in intimate relationship with the adjacent bone matrix
and had a distinctive appearance (fig. 10).
Cytoplasmic folds extended into the matrix
which had a frayed appearance. A zone of
reduced density was interposed between
the unaltered bone and the matrix subjacent to the brush border. Free, needleshaped crystals and amorphous material
were present at the osteoclast-bone interface and in spaces between folds of the
brush border. Unmineralized collagen
fibers were observed aligned perpendicularly to the osteoclast surface and extending into the brush border (fig. 11). The
clefts between the folds were tortuous and
terminated in sac-like vacuoles and dilatations. Crystals were observed in many of
these vacuoles. Larger vacuoles and vesicles were present further away from the
brush border. The folds of the brush border
contained ribosomes and fine cytoplasmic
filaments (fig. 10).
Matrix. The mineralization of organic
matrix occurred in three successive stages,
viz. calcified cartilage, woven bone, and
lamellar bone. The matrix surrounding
hypertrophic chondrocytes contained mineralized cartilage and small foci of mineralization (fig. 1 ). The mineralized cartilage
was more dense than bone and was demarcated from it by a narrow zone of reduced density. Initial loci of mineralization
and nodules of bone occurred in the osteoid
around and remote from calcified cartilage
(fig. 6 ) . Collagen fibrils within the osteoid
varied in size and ranged from 200 to
1000 A in their greatest diameter with a
mean of 425 A. The interface between
osteoid and bone was usually abrupt but
in some areas numerous nodules of bone
resulted in a more gradual transition
(figs. 2, 5).
Woven bone was formed by the coalescence of nodules of bone in osteoid. It was
characterized by bundles of mineralized
collagen fibrils of irregular size which were
loosely arranged and randomly oriented
(fig. 7). Lamellar bone replaced woven
bone and appeared as alternating bundles
of mineralized collagen in which the long
axes of the fibrils were in parallel array
and changes in direction occurred in successive strata rather than with individual
fibrils (figs. 8, 9). Cross-striations of collagen fibrils within the lamellae were in
register with each other (fig. 8). Osteocytes
located in lamellar bone tended to be fusiform with the long axis parallel to the axis
of the lamellae while osteocytes in woven
bone were more rounded.
The type and amount of mineralized
matrix varied in pigs of different ages.
Mineralized cartilage was not observed in
pigs over 17 days of age. The predominant
bone matrix in the youngest pigs was nonlamellar, woven bone while in pigs 59 to
101 days of age lamellar bone predominated.
Bone cells in the nasal turbinates of
young pigs had ultrastructural features
characteristic of their function in either
the formation or resorption of bone matrix.
Osteoblasts were associated with areas of
abundant osteoid, had an extensive rough
endoplasmic reticulum, and contained
Golgi cisternae distended with a distinctly
fibrillar material. Bud-like projections protruded from the distended cisternae, suggesting release of the contents in the form
of small vesicles. The possible role of these
vesicles in the transport and release of collagen precursors was not determined. Cameron ('69) suggested that vesicles may be
capable of transporting material to the
plasma membrane for secretion but considered their numbers to be insufficient to
form matrix at the rate it is normally laid
down. Further, the vesicles did not appear
to fuse with the plasma membrane.
Large intracytoplasmic aggregates of
intermeshed filaments were observed in the
vicinity of the plasma membrane in osteoblasts. The relationship of the filaments to
early collagen formation was not clear.
They usually were adjacent to the plasma
membrane, extended into cytoplasmic processes, and resembled the intracytoplasmic
filaments in fibroblasts described by Ross
and Benditt ('61). They were not restricted
to the poorly developed cortical zone as
they were in rats (Cameron, '61). While it
is well established that osteoblasts secrete
collagen or its precursors, the method by
which they do this remains uncertain. Previous investigators have reported direct
communication between the endoplasmic
reticulum and the extracellular space
(Sheldon and Robinson, '61; Porter, '66).
In pigs the endoplasmic reticulum frequently occurred at the periphery of the
cell but fusion with the plasma membrane
was not demonstrated. Godman and Porter
('60), and Porter ('64) reported that osteoblasts lose a portion of the cortical cytoplasm as a form of apocrine secretion.
Chapman ('61) suggested that collagen
precursors are released by the disintegration of the plasma membrane followed by
release of cytoplasmic material into the
extracellular space. The indistinct plasma
membrane on surfaces adjacent to osteoid
formation and in cell processes support the
possibility of apocrine secretion, or a variation of it, by osteoblasts in the nasal turbinates of pigs.
Bone cells in the nasal turbinates had
mitochondria which contained rosettes of
dense granules. They occurred predominantly in osteoblasts with ultrastructural
characteristics of active synthesis of organic matrix and adjacent to newly formed
osteoid. Similar mitochondrial granules
have been reported in a variety of tissues
involved in ion transport (Martin and Matthews, '69). Osteoblasts in the region of
new osteoid have been reported to have a
higher number of mitochondrial granules
than adjacent osteoblasts associated with
mature bone (Matthews et al., '70).
The predominant form of osteocyte in
nasal turbinates had a paucity of organelles and no evidence of bone formation or
resorption. However, osteocytes with well
developed organelles were observed in
which the space between the cell and the
wall of the lacuna was filled with collagen
fibers undergoing mineralization suggestive
of bone formation. The occurrence of an
occasional osteocyte with an irregular
plasma membrane, widened limiting
sheath containing a zone of finely granular
material, and a roughened lacunar wall
indicated perilacunar resorption or osteolysis. Baud ('68) reported osteocytes to be
capable of both formation and resorption
of bone. Osteocytes concerned with resorption were characterized by lysosome-like
bodies, folds in the plasma membrane sug-
gesting microphagocytisis, swollen mitochondria, and evidence of resorption in the
perilacunar bone matrix.
The presence of unmineralized collagen
fibers within the folds of the brush border
of osteoclasts differs from the findings of
some investigators (Dudley and Spiro, '61;
Gonzales, '69; Gonzales and Karnovsky,
'6 1). They interpreted the presence of crystals and the absence of collagen fibrils as
an indication that the organic matrix was
removed first leaving behind the inorganic
debris. Our results were similar to observations by Cameron ('63) and support the
concept of Hancox and Boothroyd ('61)
that removal of bone proceeds in reverse
order to the process of bone formation, viz.
loss of crystals followed by unmasking of
This study was supported in parts by
grants AM-13011, FR-5463, GM-1052, and
research fellowship award 1-F3-CA-33,53101 (Dr. Fetter), National Institutes of
Health, United States Public Health
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1 Hypertrophic chondrocyte in the nasal turbinate of a seventeen day-old
pig. The extracellular matrix consists of mineralized cartilage (CC),
loci of mineralization (long arrows), and an interlacing network of
fine fibrils ( F ) . Numerous short cytoplasmic prccesses extend from
the surface of the cell (short arrows). The cytoplasm contains flattened sacs of endoplasmic reticulum (ER), clusters of ribosomes (I),
cytoplasmic filaments ( c f ) , dense bodies (D), lipid droplets (L), and
scattered small mitochondria ( M ) . Glutaraldehyde. x 13,950.
Mature oseoblast in the nasal turbinate of a ten-day-old pig. Cytoplasmic processes (CP) extend into the osteoid ( 0 ) in which numerous
initial loci of mineralization (short arrows) and nodules of bone (long
arrows) are present. A narrow cortical zone ( c ) separates the organelles and plasma membrane. The cytoplasm contains abundant endoplasmic reticulum (ER), a prominent Golgi apparatus ( G ) associated
with numerous vesicles ( v ) , dense bodies (D), and scattered mitochondria ( M ) . Osteoblast nucleus ( N ) . Glutaraldehyde. x 11,025.
Arthur W. Fetter and Charles C. Capen
Cytoplasm of a mature osetoblast with extensive endoplasmic reticulum (ER) and a prominent perinuclear Golgi complex (G). A budlike projection extends from the membrane of one distended cisternac
(short arrow) and numerous vesicles ( v ) are present near the Golgi
apparatus. Distended cisternae of endoplasmic reticulum (long arrow),
a centriole (Ce), mitochondria ( M ) , and cytoplasmic processes (CP)
are present. Ten-day-old pig. Glutaraldehyde, x 22,500. Insert: Higher
magnification of Golgi cisternae distended by fibrillar material. x
4 Aggregations of cytoplasmic fibrils (cf) near the plasma membrane in
an osteoblast of the nasal turbinate. The bundles of fibrils displace the
abundant endoplasmic reticulum (ER) and are present in the numerous cytoplasmic processes (CP) which extend into the surrounding
Dense body (D). Fifty-nine-day-old pig. Glutaraldehyde.
osteoid (0).
x 19,800. Insert: Higher magnification of cytoplasmic fibrils and rosettes of dense granules in mitochondria. x 22,100.
Arthur W. Fetter and Charles C. Capen
5 Portions of three osteoblasts each of which have rough-surfaced depressions in the plasma membrane or rough-surfaced vesicles within the
cytoplasm (arrows). The cytoplasm contains urofiles of endoplasmic
reticulum ( E R ) , mitochondria ( M ) , and ribosomes ( r ) . Cytoplasmic
processes (CP) and osteoid ( 0 ) are seen i n the extracellular space.
Twenty-four-day-old pig. Glutaraldehyde. x 18,425.
6 Immature osteocyte completely surrounded by osteoid containing numerous nodules of bone (long arrows). The cell has ultrastructural
characterietics that are intermediate between mature osteoblasts and
osteocytes. The outline is more round but the cytoplasm contains organelles in similar numbers to osteoblasts. The cisternae of the endoplasmic reticulum are distended (ER). Membranes of the Golgi complex
( G ) contain a fibrillar material and bud-like projections extened from
the surface (short arrows). Dense bodies ( D ) and mitochondria ( M )
are present. One hundred-one-day-old pig. Glutaraldehyde. x 8,200.
Arthur W. Fetter and Charles C. Capen
7 Mature osteocyte located superficially in a trabecula of woven bone
(WB) in the nasal turbinate of a ten-day-old pig. Mineralization of
osteoid (0)does not appear to be complete on the surface adjacent
to osteoblasts (OB). Cytoplasmic processes (CP) of the osteocyte are
seen within the lacuna. The limiting sheath (opposing long arrows) i s
narrow on the surface containing little osteoid. The plasma membrane
of the osteocyte is straight and the cytoplasm contains individual profiles of endoplasmic reticulum (ER), ribosomes ( r ) , rough-surfaced
vesicles (short arrow), dense bodies ( D ) , and mitochondria with electron-dense granules (M). Glutaraldehyde. x 14,450.
Mature osteocyte in a lacuna with a n irregular and roughened surface.
The limiting sheath is widened (opposing long arrows) and contains a
zone of finely granular material of moderate density and loose collagen
fibrils. The plasnia membrane is irregular i n outline and has numerous
invaginations. The cytoplasm contains profiles of endoplasmic reticulum (ER), cytoplasmic filaments (cf), swollen mitochondria with
electron-dense granules (M), and dense bodies (D). The perilacunar
matrix is reduced in density and cross striations of collagen fibrils are
in register (short arrow) in the predominantly lamellar bone (LB ) .
Forty-five-day-old pig. Glutaraldehyde. x 13,800.
Arthur W. Fetter a n d Charles C. Capen
Osteoclast in close proximity to a trabecula of lamellar bone (LB) in
the nasal turbinate of a thirty-eight-day-old pig. Large Golgi complexes
( G ) are present near the two nuclei ( N ) . The abundant mitochondria
( M ) vary from round to rod like in profile and contain numerous dense
granules. Vacuoles ( V ) and dense bodies (short arrows) are numerous,
especially in the vicinity of the Golgi apparatus and brush border
(BB). Glutamldehyde. x 5,500.
10 Interface between the brush border of a n osteoclast and bone. Numerous needle-shaped crystals and amorphous material are free at the
bone surface and present within the folds and terminal sacs of the
brush border (long arrows ). Rough-surfaced vesicles (short arrows)
appear to be forming in the area of the terminal sacs. Vacuoles ( V ,
in the osteoblast contain no visible crystals. Ribosomes ( r ) are the only
organelles present within the cytoplasmic processes. A narrow zone of
reduced density is present in the bone a t the bottom. A cross-section
of a n osteocytic process ( P ) is seen at the lower left. Fifty-nine-day-old
pig. Glutaraldehyde. x 20,250.
11 Brush border-bone interface in the nasal turbinate of a seventeenday-old pig. Collagen fibrils devoid of mineral (long arrows) and
needle-shaped crystals (short arrows) are seen within folds and terminal sacs formed by cytoplasmic processes of the brush border. Glutaraldehyde. X 21,500.
Arthur W. Fetter and Charles C. Capen
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young, pigs, structure, turbinates, nasal, fine, bones
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