Histological Organization of Bone
Compact Bone
Compact bone consists almost entirely of extracellular substance, the
matrix. Osteoblasts deposit the matrix in the form of
thin sheets which are called
lamellae. Lamellae
are
microscopical structures. Collagen fibres
within each lamella run parallel to each other. Collagen fibres which belong to
adjacent lamellae run at oblique angles to each other. Fibre density seems
lower at the border between adjacent lamellae, which gives rise to the lamellar
appearance of the tissue. Bone which is composed by lamellae when viewed under
the microscope is also called
lamellar bone.
In the process of the deposition of the matrix, osteoblasts become encased
in small hollows within the matrix, the
lacunae.
Unlike chondrocytes, osteocytes have several thin processes, which extend from
the lacunae into small channels within the bone matrix , the
canaliculi. Canaliculi arising from one lacuna may
anastomose with those of other lacunae and, eventually, with larger,
vessel-containing canals within the bone. Canaliculi provide the means for the
osteocytes to communicate with each other and to exchange substances by diffusion.
In mature compact bone most of the individual lamellae form concentric rings
around larger longitudinal canals (approx. 50 µm in diameter) within the bone
tissue. These canals are called
Haversian canals.
Haversian canals typically run parallel to the surface and along the long axis
of the bone. The canals and the surrounding lamellae (8-15) are called a
Haversian system or an
osteon.
A Haversian canal generally contains one or two capillaries and nerve fibres.
Irregular areas of
interstitial lamellae,
which apparently do not belong to any Haversian system, are found in between
the Haversian systems. Immediately beneath the periosteum and endosteum a few
lamella are found which run parallel to the inner and outer surfaces of the
bone. They are the
circumferential lamellae and
endosteal lamellae.
A second system of canals, called
Volkmann's canals,
penetrates the bone more or less perpendicular to its surface. These canals
establish connections of the Haversian canals with the inner and outer surfaces
of the bone. Vessels in Volkmann's canals communicate with vessels in the
Haversian canals on the one hand and vessels in the endosteum on the other. A
few communications also exist with vessels in the periosteum.
Trabecular Bone
The matrix of trabecular bone is also deposited in
the form of lamellae. In mature bones, trabecular bone will also be
lamellar bone. However,
lamellae in trabecular bone do
not form Haversian systems. Lamellae of trabecular bone are deposited on
preexisting trabeculae depending on the local demands on bone rigidity.
Osteocytes, lacunae and canaliculi in trabecular bone resemble those in
compact bone.
Note the distinction between
macroscopic (visible to the eye) and microscopic (only visible under the
microscope) appearance when the bone is named. Lamellar bone forms both
trabecular bone and compact bone, which are the two macroscopically
recognizable bone forms.
Suitable Slides
sections of compact
bone (usually part of the diaphysis of a long bone) - ground (unstained), Schmorl stained
or H&E
Compact bone, human -
Schmorl stain
Lamellae which run parallel to the surface of the bone are visible both on the
outer, convex surface of the bone (circumferential lamellae) and on the inner,
concave surface of the bone facing the marrow cavity (endosteal lamellae). The
surface formed by the endosteal lamellae is often more irregular than the
surface formed by the circumferential lamellae. The space between these two
sets of lamellae is filled by Haversian systems and interstitial lamellae. Only
few of the Haversian systems are "textbook" circular. Osteocyte
lacunae are visible between the lamellae. Canaliculi become visible at high
magnification (illustrated in the ground section below).
You should be able to see, draw and identify Haversian
systems, interstitial and circumferential lamellae and/or endosteal lamellae.
Compact bone, human -
ground (unstained)
The osteocyte lacunae are the main feature of the ground section. They are
visible as elongated black spots in the bone matrix. Canaliculi, radiate from
the lacunae into the surrounding bone matrix. Some lamellae are visible in the
ground section. There is actually no distinct border between most lamellae, but
our brain can use the elongated osteocyte lacunae and their orientation to
"reconstruct" the lamellae. Volkman's canals connect to a few of the
Haversian canals.
Suitable Slides
sections of part of a vertebra or
an epiphysis of a long bone - H&E, van Gieson
Sections prepared to show articular cartilage will
often also contain trabecular bone in the epiphysis below the articular
cartilage.
Articular cartilage,
bovine - H&E
Thin sheets and bars of bone, trabeculae, are visible at low magnification.
Although they may appear as individual pieces in sections, they form an
interconnected meshwork in the living bone. The spaces between the trabeculae,
the marrow cavity of the epiphysis, is filled by either red bone marrow or
yellow bone marrow. At high magnification, elongated osteocyte lacunae, which
in well preserved tissue still contain osteocytes, are visible in the matrix.
If the H&E stain also turned out well, it should be visible that the matrix
of the trabecular bone is formed by lamellae. Canaliculi are present but hard
to identify in most H&E stained sections. Haversian systems are not present in the trabeculae.
In trabecular bone obtained from young individuals, in which the bone is still
growing, small areas of calcified cartilage are occasionally seen in the bone
trabeculae. They are remnants of the cartilage scaffold on which bone matrix
was deposited during the formation of the trabeculae. With the reorganisation
of bone such areas will eventually be lost.
![thumbnail]( "Histological Organization of Bone")
Title:
Histological Organization of Bone
by:
om
at
2013-02-15T03:01:00+07:00
Rating: 4.8
of 5 Reviews
Histological Organization of Bone